• Physics Core Facilities
  • Physics of Complex Systems
  • Condensed Matter Physics
  • Particle Physics and Astrophysics
  • SRITP
Date:
Colloquia
25
November, 2021
Thursday
Hour: 11:15-12:30

Physics Colloquium

Ady Stern
Electronic resistance is a fundamental notion both in condensed matter physics and in everyday life, where it is a source of heating caused by electronic currents. Typically, resistance originates from electrons scattering off impurities. However, even a perfectly clean system harbors a resistance, inversely proportional to the number of its conduction channels. Recent theories have shown that scattering of the flowing electrons off one another reduces this resistance, raising the question of its lower bound. Here we show that for a fixed number of channels the resistance may be practically eliminated, and give a transparent physical picture of this elimination.
Date:
Colloquia
18
November, 2021
Thursday
Hour: 11:15-12:30

Physics Colloquium

Alexander Milov
A state of matter whose constituents are quarks and gluons governed by strong force interactions is a fascinating state of matter. This “Quark-Gluon Plasma” can be created in collisions of heavy ions at high energy. Since the beginning of ion collisions at the LHC in 2010, the heavy-ion program has produced a series of very interesting and sometimes surprising discoveries from the four major LHC experiments. These findings not only changed our understanding of the new state of matter but also gave us new tools to study it. In this talk I’ll review the heavy-ion research program ongoing at the ATLAS detector, and show how the discoveries made a few years ago have become new instruments to understand the laws of quantum chromodynamics.
Date:
Seminars
16
November, 2021
Tuesday
Hour: 13:15-14:15

AMOS Seminar

Prof. Dan Oron
Department of Physics of Complex Systems
When Hanbury-Brown and Twiss proposed to use photon correlations for stellar interferometry in 1954 the idea was received with great skepticism. Yet, the use of photon correlations for various uses, from identification of quantum emitters to emitter counting grew over the years. In the talk, I will describe some of our efforts in using HBT correlations and their derivatives in superresolution microscopy and in advanced spectroscopy of quantum emitters, as well as the technological advances enabling this.
Date:
Colloquia
04
November, 2021
Thursday
Hour: 11:15-12:30

Physics Colloquium

Gershon Kurizki
Thermodynamics requires a system to equilibrate with its thermal environment, alias a bath. However, our results over the years have shown that, surprisingly, nonintrusive observations of a quantum system may heat or cool it, thus preventing the equilibration [1,2]. Recently, we have shown that also the bath state, which is considered immutable in thermodynamics, is dramatically changed by a quantum probe and its observations [3]. These effects stem from the unavoidable entanglement between quantum systems and baths even when they are weakly coupled, thus undermining the tenets of thermodynamics in the quantum domain. Most remarkably, we have recently demonstrated that probe observations can render thermal bath states nearly pure [4]. The implications are far reaching, most prominently the ability to reverse the time arrow of the entire system-bath compound, by causing its quantum coherent oscillation. This raises the question: Is thermodynamics, which rests on the concept of a bath, compatible with quantum mechanics? It may appear necessary to assume that a quantum working medium in a heat machine is dissipated by a bath [5,6]. Yet, most recently, we have shown that heat machines can be perfectly coherent, non-dissipative devices realized by nonlinear interferometers fed by few thermal modes [7], so that baths are redundant. Finally, I will discuss the ability of observers to commute information to work [8] and speculate on the role of observers in physics [9]. References to our work 1. Nature 452, 724 (2008). 2. PRL 105,160401 (2010). 3. NJP 22, 083035 (2020). 4. Arxiv 2108.09826 (2021) 5. Nat. Commun. 9, 165 (2018). 6. PNAS 115, 9941 (2018); PNAS 114, 12156 (2017). 7. Arxiv2108.10157 (2021). 8. PRL 127, 040602 (2021). 9. G.Kurizki and G. Gordon, “The Quantum Matrix” (Oxford Univ. Press, 2020).
Date:
Seminars
18
October, 2021
Monday
Hour: 12:30

Joint DPPA and AMOS Seminar

Ben Ohayon
Bound exotic systems offer unique opportunities to test our understanding of the tenets of modern physics and determine fundamental constants. By comparing measured transitions between antihydrogen and hydrogen, we can search for CPT violation, which may explain the observed baryon asymmetry in the universe while respecting the stringent bounds on CP violation within the standard model. The comparison of the energy levels of muonium (M) with their clean theoretical prediction searches for new physics in a multitude of scenarios such as Lorentz and CPT violation in the muonic sector, and new bosons coupled to leptons. Such particles are motivated by the persistent discrepancy between the recently remeasured anomalous magnetic moment of the muon and its theoretical prediction, arguably the most promising hint to new physics in decades. In this talk I will review ongoing work for antihydrogen and M spectroscopy at CERN and PSI, and present our recent measurement of the Lamb-Shift in M, comprising an order of magnitude of improvement upon the state of the art and the first improvement to M energy levels in 20 years. I will conclude by showing that pushing M spectroscopy to its limits could independently determine the muon g-2 with enough accuracy to shed light on the puzzle.
Date:
Seminars
07
October, 2021
Thursday
Hour: 11:00

NPOD at LUXE, new physics search with optical dump

Prof. Gilad Perez & Dr. Noam Tal-Hod
Department of Particle Physics and Astrophysics
We propose a novel way to search for feebly interacting massive particles, exploiting two properties of systems involving collisions between high energy electrons and intense laser pulses. The first property is that the electron-intense-laser collision results in a large flux of hard photons, as the laser behaves effectively as a thick medium. The second property is that the emitted photons free-stream inside the laser and thus for them the laser behaves effectively as a very thin medium. Combining these two features implies that the electron-intense-laser collision is an apparatus which can efficiently convert UV electrons to a large flux of hard, co-linear photons. We further propose to direct this unique large and hard flux of photons onto a physical dump which in turn is capable of producing feebly interacting massive particles, in a region of parameters that has never been probed before. We denote this novel apparatus as ``optical dump'' or NPOD (new physics sea! rch with optical dump). The proposed LUXE experiment at Eu.XFEL has all the required basic ingredients of the above experimental concept. We discuss how this concept can be realized in practice by adding a detector after the last physical dump of the experiment to reconstruct the two-photon decay product of a new spin-0 particle. We show that even with a relatively short dump, the search can still be background-free. Remarkably, even with a 40 TW laser, which corresponds to the initial run, and definitely with a 350 TW laser, of the main run with one year of data taking, LUXE-NPOD will be able to probe uncharted territory of both models of pseudo-scalar and scalar fields, and in particular probe natural of scalar theories for masses above 100 MeV.
Date:
Colloquia
24
June, 2021
Thursday
Hour: 11:15-12:30

Synchronization and spatial coherence of noisy circadian clocks in a multicellular1-d organism

Joel Stavans
The collective behavior of oscillators is a venerable subject in Physics since Huygens’ seminal contributions. Living systems, from simple unicellular bacteria to multicellular plants and mammals also display oscillatory dynamics, the most conspicuous of which are circadian rhythms, coupling the biology of these organisms to day/night cycles on Earth. While considerable headway has been made in understanding the behavior of individual circadian clocks and their molecular components, the behavior of a large collection of clocks is still poorly understood, constituting a fertile ground of inquiry. We studied at the single-cell level the collective behavior of one-dimensional arrays of clocks in Anabaena, a cyanobacterial organism of ancient origin, as a model system. Anabaena filaments display remarkable synchrony and spatial coherence at the organismal scale, despite considerable and yet inevitable fluctuations in each cell –demographic noise-, stemming from the stochastic nature of biochemical reactions. Furthermore, we provide experimental evidence supporting the notion that spatio-temporal coherence is largely due to the coupling of clocks by cell-cell communication, and that the clock controls other cellular processes such as cell division. A stochastic, one-dimensional toy model of coupled clocks shows that demographic noise can seed stochastic oscillations outside the region where deterministic limit cycles with circadian periods occur. The model reproduces the observed spatio-temporal coherence along filaments and provides a robust description of coupled circadian clocks in a multicellular organism.
Date:
Colloquia
17
June, 2021
Thursday
Hour: 11:15-12:30

ULTRASAT: Revolutionizing our view of the transient universe

Eli Waxman
ULTRASAT is a scientific satellite, that is planned to be launched to a geo-stationary orbit in Q4 2024. It will carry a telescope with an unprecedentedly large field of view (200 squared degrees) and UV (220-280nm) sensitivity. These unique properties will enable us to detect and systematically study transient astronomical events within an extra-Galactic volume, that is hundreds of time larger than that accessible to current observatories. ULTRASAT’s measurements will have a broad science impact across the fields of gravitational wave sources, supernovae, variable and flare stars, active galactic nuclei, tidal disruption events, compact objects, and galaxies. In this talk I will review ULTRASAT’s key science goals, its unique technical properties, and the project’s structure and status.
Date:
Colloquia
22
April, 2021
Thursday
Hour: 11:15-12:30

Atmospheric Dynamics on Jupiter: New Results from the Juno Mission

Yohai Kaspi
NASA's Juno Mission is now completing its 5 year nominal mission around Jupiter, orbiting the planet in an eccentric polar-orbit every 53 days. One of the prime mission objectives is better understanding the atmospheric dynamics through gravitational, microwave, infrared and magnetic measurements. In this talk, we will focus on three new results explaining different aspects of the dynamics on Jupiter. First, infrared imaging data revealed that Jupiter’s poles are surrounded by 5 cyclones around the North Pole and 8 cyclones around the South Pole. We explain the location, size and stability of these circumpolar cyclones based on vorticity dynamics. Second, using microwave data, revealing Jupiter’s deep ammonia abundance structure, we show that Jupiter has 8 meridional circulation cells in each hemisphere. These cells resemble in their governing physics Earth's midlatitude Ferrel cells, and relate to the observed red and white belts and zones at Jupiter’s cloud-level. Finally, using Juno’s gravity measurements we constrain the depth of Jupiter’s east-west jet-streams, and the depth (mass) of the most iconic vortex in the Solar system — Jupiter’s Great Red Spot. Overall, this unique multiple instrument dataset allows now explaining the governing physics of several outstanding aspects of Jupiter’s internal and atmospheric dynamics. We will also compare the dynamics to those of Saturn, generalizing some of the this new understanding.
Date:
Colloquia
18
March, 2021
Thursday
Hour: 11:15-12:30

Solving computational problems with coupled lasers

Nir Davidson
Computational problems may be solved by realizing physics systems that can simulate them. Here we present a new system of coupled lasers in a modified degenerate cavity that is used to solve difficult computational tasks. The degenerate cavity possesses a huge number of degrees of freedom (300,000 modes in our system), that can be coupled and controlled with direct access to both the x-space and k-space components of the lasing mode. Placing constraints on these components are mapped on different computational minimization problems. Due to mode competition, the lasers select the mode with minimal loss to find the solution. We demonstrate this ability for simulating XY spin systems and finding their ground state, for phase retrieval, for imaging through scattering medium, and more.
Date:
Seminars
13
January, 2021
Wednesday
Hour: 11:00

Primordial black holes as dark matter: The good, the bad and the ugly

Prof.Alfredo Urbano
Department of Particle Physics and Astrophysics
In this seminar, I will consider the possibility that the totality of dark matter consists of atomic-size black holes of primordial origin. I will review the basics of this proposal, and I will discuss some key questions yet unsolved.
Date:
Colloquia
07
December, 2020
Monday
Hour: 16:00-17:15

Israel Physics Colloquium

Ashvin Vishwanath
For decades, condensed matter systems have been studied within the framework of classical order parameters - i.e. the Landau-Wilson paradigm. This has been recently extended with the rather complete understanding of topological states of noninteracting electrons. In this talk I will focus instead on new physics that arises from the interplay of topology and strong interactions. A unifying theme will be the emergence of gauge fields rather than the classical order parameters of Landau theory. I will illustrate these general themes with two recent works. The first proposes a route to realizing a long sought after phase - the Z2 quantum spin liquid - in a synthetic platform, an array of highly excited (Rydberg) atoms [1]. A potential application to the engineering of naturally fault tolerant quantum bits will also be described. The second example describes a topological route to strong coupling superconductivity [2], which was inspired by recent experimental observations in magic angle bilayer graphene and related devices. [1] arXiv:2011.12310. Prediction of Toric Code Topological Order from Rydberg Blockade. Authors: R. Verresen, M. Lukin and A. Vishwanath. [2]arXiv:2004.00638. Charged Skyrmions and Topological Origin of Superconductivity in Magic Angle Graphene. Authors: E. Khalaf, S. Chatterjee, N. Bultinck, M. Zaletel, A. Vishwanath.
Date:
Colloquia
23
November, 2020
Monday
Hour: 16:00-17:15

IPC - Novel Probes of Dark Matter

Cora Dvorkin
Cosmological observations and galaxy dynamics seem to imply that 84% of all matter in the universe is composed of dark matter, which is not accounted for by the Standard Model of particles. The particle nature of dark matter is one of the most intriguing puzzles of our time. The wealth of knowledge which is and will soon be available from cosmological surveys will reveal new information about our universe. I will discuss how we can use new and complementary data sets to improve our understanding of the particle nature of dark matter. In particular, galaxy-scale strong gravitational lensing provides a unique way to detect and characterize dark matter on small scales. I will present advances in the analysis of gravitational lenses and identification of small-scale clumps using machine learning. I will introduce the convergence power spectrum as a promising statistical observable that can be extracted from strongly lens images and used to distinguish between different dark matter scenarios, showing how different properties of the dark matter get imprinted at different scales. I will also discuss the different contribution of substructure and line-of-sight structure to perturbations in strong lens images.
Date:
Colloquia
19
November, 2020
Thursday
Hour: 11:15-12:30

Bringing noble-gas spins into the light

Ofer Firstenberg
In quantum science, we often encounter the tension between elongating the coherence time of a system and retaining the ability to control and interact with it. An extreme example is the nuclear spin of noble gases, which is isolated from the environment by the complete electronic shells. In our lab, the spins of a helium-3 gas maintain coherence for up to two hours. Unfortunately, these spins are not accessible to light in the optical domain, and their (potential) quantum qualities have been beyond reach and largely overlooked. We establish that thermal spin-exchange collisions between noble-gas atoms and alkali-metal atoms form a quantum interface between them. These weak collisions, despite their stochastic nature, accumulate to a deterministic, efficient, and controllable coupling between the collective spins of the two gases. In experiments, we realize the strong coupling between potassium and helium-3 spins and, by coupling light to the potassium spins, demonstrate an efficient, two-way, optical interface to the helium-3 spins. The interface paves the way to employing noble-gas spins in the quantum domain, and we discuss prospects for quantum memories and entanglement of distant noble-gas ensembles with hour-long lifetimes.
Date:
Colloquia
09
November, 2020
Monday
Hour: 16:00-17:15

IPC - Nov 09 - Jesse Thaler

Jesse Thaler
Collision Course: Particle Physics meets Machine Learning Modern machine learning has had an outsized impact on many scientific fields, and particle physics is no exception. What is special about particle physics, though, is the vast amount of theoretical and experimental knowledge that we already have about many problems in the field. In this colloquium, I present two cases studies involving quantum chromodynamics (QCD) at the Large Hadron Collider (LHC), highlighting the fascinating interplay between theoretical principles and machine learning strategies. First, by cataloging the space of all possible QCD measurements, we (re)discovered technology relevant for self-driving cars. Second, by quantifying the similarity between two LHC collisions, we unlocked a class of nonparametric machine learning techniques based on optimal transport. In addition to providing new quantitative insights into QCD, these techniques enable new ways to visualize data from the LHC.
Date:
Colloquia
05
November, 2020
Thursday
Hour: 11:15-12:30

Geometric Frustration and the Intrinsic Approach in Soft Condensed Matter

Efi Efrati
Deducing the emergent behavior of a material from the properties of its molecular or atomic constituents is one of the greatest challenges of condensed matter theory. Considering many-body systems with highly cooperative ground states renders this task even more challenging. Geometrically frustrated assemblies are comprised of ill-fitting constituents that are associated with two or more tendencies that cannot be simultaneously reconciled, and thus lack a stress free rest state. The ground state of frustrated assemblies is highly cooperative, leading them to exhibit super-extensive energy growth, filamentation, size limitation and exotic response properties. Such systems arise in naturally occurring structures in biology and organic chemistry as well as in manmade synthetic materials. In this talk I will discuss how the intrinsic approach, in which matter is described only through local properties available to an observer within the material, overcomes the lack of a stress free rest state for frustrated assemblies and leads to a general framework. This framework in particular allows predicting the super-extensive energy exponent for sufficiently small systems. I will discuss its application to several specific systems exhibiting geometric frustration: growing elastic bodies, frustrated liquid crystals and twisted molecular crystals.
Date:
Colloquia
26
October, 2020
Monday
Hour: 16:00-17:15

Online Israel Physics Colloquium: "The magic of moiré quantum matter"

Pablo Jarillo-Herrero
The understanding of strongly-correlated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultra-cold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, namely moiré quantum matter. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a strongly-correlated electronic system. These flat bands systems exhibit a plethora of quantum phases, such as correlated insulators, superconductivity, magnetism, Chern insulators, and more. Furthermore, it is possible to extend the moiré quantum matter paradigm to systems beyond magic angle graphene, and I will present an outlook of some exciting directions in this emerging field.
Date:
Colloquia
22
October, 2020
Thursday
Hour: 11:15-12:30

From Ultralight Dark Matter to Snowballs in Hell: a Tour in Particle Astrophysics

Kfir Blum
Astrophysical phenomena play a definitive role in our understanding of fundamental particle physics, and vice-verse. I will present two lines of research, showcasing the interplay between particle physics theory and astrophysics. In the first half of the talk, I will show how the viable parameter space for dark matter can be established using gravity alone. At the lowest end of the possible range for the dark matter particle mass, the de Broglie wavelength of ultralight dark matter (ULDM) attains astronomical scales. The ensuing wave mechanics phenomena can be tested observationally in a variety of astrophysical systems. I will describe a search for the imprint of ULDM on the gas kinematics of low-surface-brightness galaxies, leading to an absolute lower bound on the mass of dark matter. A host of other systems, ranging from supermassive black holes to gravitational lensing, offer promising means to advance the search for ULDM by orders of magnitude. In the second half of the talk, I will show how an analysis of cosmic ray antimatter — long considered a smoking gun for dark matter in the TeV range — has taken a surprising turn, leading us to new theoretical insights on the problem of the origin of loosely-bound nuclei in hadronic collisions (sometimes referred to as ``Snowballs in Hell”). The resulting research programme, now explored at the Large Hadron Collider, offers a bridge between two-particle correlation analyses to the study of nuclear clusters.
Date:
Colloquia
15
October, 2020
Thursday
Hour: 11:15-12:30

Lifshitz theory of the cosmological constant

Ulf Leonhardt
The cosmological constant, also known as dark energy, was believed to be caused by vacuum fluctuations, but naive calculations give results in stark disagreement with fact. In the Casimir effect, vacuum fluctuations cause forces in dielectric media, which is very well described by Lifshitz theory. Recently, using the analogy between geometries and media, a cosmological constant of the correct order of magnitude was calculated with Lifshitz theory [U. Leonhardt, Ann. Phys. (New York)  411, 167973 (2019)]. This lecture discusses the empirical evidence and the ideas behind the Lifshitz theory of the cosmological constant without requiring prior knowledge of cosmology and quantum field theory.
Date:
Colloquia
24
September, 2020
Thursday
Hour: 11:15-12:30

Visualizing Strongly-Interacting Quantum Matter

Shahal Ilani
When quantum mechanics and Coulomb repulsion are combined in a pristine solid, some of the most fascinating electronic phases in nature can emerge. Interactions between electrons can form correlated insulators, electronic liquids, and in extreme cases even quantum electronic solids. These phases are predicted to exhibit their most striking features in real-space, however, they are also extremely fragile, preventing their visualization with existing experimental tools. In this talk, I will describe our experiments that use a pristine carbon nanotube as a new type of a scanning probe, capable of imaging electrical charge with unprecedented sensitivity and minimal invasiveness. I will show how using this platform we were able to obtain the first images of the quantum crystal of electrons, visualize the collective hydrodynamic flow of interacting electrons in graphene, and unravel the parent state that underlies the physics of strongly-interacting electrons in the recently-discovered system of magic angle twisted bilayer graphene.
Date:
Colloquia
10
September, 2020
Thursday
Hour: 11:15-12:30

Toward autonomous artificial cells on a chip

Roy Bar-Ziv
We study the assembly of programmable DNA compartments as “artificial cells” on a chip from the single cell level to multicellular architecture and communication. We will describe recent progress toward autonomous self-synthesis and assembly of cellular machines, memory transactions, fuzzy decision-making, synchrony and pattern formation, as well as electric field manipulation of gene expression.
Date:
Colloquia
27
August, 2020
Thursday
Hour: 11:15-12:30

Quantum Critical Metals

Erez Berg
Metallic quantum critical phenomena are believed to play a key role in many strongly correlated materials, including high temperature superconductors. Theoretically, the problem of quantum criticality in the presence of a Fermi surface has proven to be highly challenging. However, it has recently been realized that many models used to describe such systems are amenable to numerically exact solution by quantum Monte Carlo (QMC) techniques, without suffering from the fermion sign problem. I will review the status of the understanding of metallic quantum criticality, and the recent progress made by QMC simulations. The results obtained so far will be described, as well as their implications for superconductivity, non-Fermi liquid behavior, and transport in the vicinity of metallic quantum critical points. Some of the outstanding puzzles and future directions are highlighted.
Date:
Colloquia
13
August, 2020
Thursday
Hour: 11:15-12:30

Physical Aspects of Language: Memory, Correlations and Structure in Text and Conversation

Elisha Moses
The conversion of ideas and thoughts into a linear train of words that represents them constitutes a channel of communication that we call language. The capacity for language is a relatively recent evolutionary development in humans, and according to the theory of language established by Chomsky, humans are born with a universal “internal grammar” that enables verbal communication. Although this idea is still controversial, it has support from genetic research: Certain mutations in a gene called FOXP2 significantly impair the ability for grammar. As a natural phenomenon stemming from genes and the brain, language should thus be amenable to the tools of analysis that physics employs with other natural phenomena. We present three studies on the role of memory and correlations in language. In the first, we investigate the correlation network of words in written texts to identify a hierarchy structures that harnesses memory to bind topics of interest (‘concepts’). In the second study, we see how concepts are established by the existence of loops in a network of words linked by their definitions in a dictionary. Finally, we discuss recent work on how the music, or prosody, adds information to the text. We show that as we convert words into verbal utterances, our short-term memory creates chunks that are then spoken by the vocal chords and muscles. Our approach applies feature-based recognition, which has been extremely successful in image processing, to spoken language. Application to computerized analysis of emphasis in conversation and to the construction of a ‘prosodic dictionary’ will be discussed.
Date:
Seminars
25
June, 2020
Thursday
Hour: 09:30-10:30

Sparsity-based Methods for Rapid MRI

Dr. Efrat Shimron
Zoom Lecture: https://weizmann.zoom.us/j/99058507421 Magnetic Resonance Imaging (MRI) is a superb imaging modality that provides high-quality images of the human body. However, one of its major limitations is the long acquisition time, which hinders the MRI clinical use. The acquisition time can be shortened by acquiring less data; however, this requires suitable methods for accurate image reconstruction from subsampled data, which is acquired with a sub-Nyquist rate. In this seminar, four novel methods for image reconstruction from subsampled data will be presented. These methods build upon the well-established frameworks of Parallel Imaging (PI) and Compressed Sensing (CS), utilize a-priori knowledge about data sparsity, and address current limitations of PI-CS methods. The first two methods accelerate static MRI scans by introducing the Convolution-based Reconstruction (CORE) framework, which offers a parameter-free non-iterative reconstruction. Experiments with in-vivo 7T brain data demonstrated that these methods perform comparably to the well-established GRAPPA and l1-SPIRiT methods, with the advantage of shorter computation times and reduced need for parameter calibration. The next two developed methods accelerate dynamic MRI scans that provide temperature monitoring in High Intensity Focused Ultrasound (MRgHIFU) thermal ablation treatments. The developed methods enable rapid MR monitoring by reconstructing temperature changes from subsampled data. Validation experiments were performed with in-vivo data from clinical treatments of prostate cancer in humans; these showed that the proposed methods significantly outperform two state-of-the-art methods in the temperature reconstruction task
Date:
Seminars
22
March, 2020
Sunday
Hour: 13:15

Three-Dimensional Active Defect Loops

Gareth Alexander
We describe the flows and morphological dynamics of topological defect lines and loops in three-dimensional active nematics and show, using theory and numerical modelling, that they are governed by the local profile of the orientational order surrounding the defects. Analysing a continuous span of defect loop profiles, ranging from radial and tangential twist to wedge ±1/2 profiles, we show that the distinct geometries can drive material flow perpendicular or along the local defect loop segment, whose variation around a closed loop can lead to net loop motion, elongation, or compression of shape, or buckling of the loops. We demonstrate a correlation between local curvature and the local orientational profile of the defect loop, indicating dynamic coupling between geometry and topology. To address the general formation of defect loops in three dimensions, we show their creation via bend instability from different initial elastic distortions.
Date:
Seminars
16
March, 2020
Monday
Hour: 14:15

On energy equilibration in slow fast systems

Vered Rom-Kedar
Department of Physics of Complex Systems
. In 1949, Fermi proposed a mechanism for the heating of particles in cosmic rays. He suggested that on average, charged particles gain energy from collisions with moving magnetic mirrors since they hit the mirrors more frequently with heads on collisions. Fermi, Ulam and their followers modeled this problem by studying the energy gain of particles moving in billiards with slowly moving boundaries. Until 2010 several examples of such oscillating billiards leading to power-law growth of the particles averaged energy were studied. In 2010 we constructed an oscillating billiard which produces exponential in time growth of the particles energy. The novel mechanism which leads to such an exponential growth is robust and may be extended to arbitrary dimension. Moreover, the exponential rate of the energy gain may be predicted by utilizing adiabatic theory and probabilistic models. The extension of these results to billiards with mixed phase space leads to the development of adiabatic theory for non-ergodic systems. Finally, such accelerators lead to a faster energy gain in open systems, when particles are allowed to enter and exit them through a small hole. The implications of this mechanism on transport in extended systems and on equilibration of energy in closed systems like "springy billiards" will be discussed. The latter application provides a key principle: to achieve ergodicity in slow-fast systems in the adiabatic limit, the fast subsystems should NOT be ergodic.
Date:
Seminars
15
March, 2020
Sunday
Hour: 13:15

Recovering Lost Information in the Digital World

Yonina Eldar, WIS
Department of Physics of Complex Systems
The conversion of physical analog signals to the digital domain for further processing inevitably entails loss of information.The famous Shannon-Nyquist theorem has become a landmark in analog to digital conversion and the development of digital signal processing algorithms. However, in many modern applications, the signal bandwidths have increased tremendously, while the acquisition capabilities have not scaled sufficiently fast. Furthermore, the resulting high rate digital data requires storage, communication and processing at very high rates which is computationally expensive and requires large amounts of power. In this talk, we present a framework for sampling and processing a wide class of wideband analog signals at rates far below Nyquist by exploiting signal structure and the processing task. We then show how these ideas can be used to overcome fundamental resolution limits in optical microscopy, ultrasound imaging, quantum systems and more. We demonstrate the theory through several demos of real-time sub-Nyquist prototypes and devices operating beyond the standard resolution limits combining high spatial resolution with short integration time.
Date:
Colloquia
05
March, 2020
Thursday
Hour: 11:15-12:30

Dwarf Galaxies as Astrophysical Laboratories

Josh Simon
The dwarf galaxies orbiting the Milky Way are the oldest, least luminous, most dark matter-dominated, and least chemically evolved stellar systems known. To begin, I will provide a brief introduction to these galaxies, highlighting the recent discovery of large numbers of ultra-faint dwarf galaxies. I will then explain how we can measure their dark matter content and describe some of the numerous ways that dwarfs are being used to constrain the properties of dark matter. Finally, I will show how chemical abundance measurements of dwarf galaxy stars provided critical insight into r-process nucleosynthesis prior to the LIGO discovery of a neutron star merger.
Date:
Colloquia
27
February, 2020
Thursday
Hour: 00:00

Radiation-Dominated Black Hole Accretion Flows

James Stone
At high accretion rates, the outward force of radiation pressure generated by energy released by infalling matter can exceed the inward pull of gravity.  Such super-Eddington accretion flows occur in many systems, such as the inner regions of quasars and luminous AGN, ultra-luminous X-ray sources (ULXs), and tidal disruption events.  Understanding such flows is important not only for interpreting the spectra and variability of these sources, but also to predict the rate of growth of black holes in the early universe, and to quantify energy and momentum feedback into the medium surrounding the black hole, a process likely to be important in galaxy formation.  New results from a study of the magnetohydrodynamics of luminous accretion flows, in which radiation pressure dominates, will be presented. Our results reveal new physical effects, such as turbulent transport of radiation energy, that require extension of standard thin-disk models.  We discuss the implications of our results for the astrophysics of accreting black holes.
Date:
Colloquia
20
February, 2020
Thursday
Hour: 11:15-12:30

Designing the optimal wave

Stefan Rotter
I will speak about newly emerging approaches for designing wave fronts that are optimal for various purposes such as for focusing waves on a target, for manipulating small particles with light, or for precision measurements in general. The theoretical concept enabling the optimal solutions for all of these diverse applications turns out to be an operator introduced by  Wigner and Smith based on a system’s scattering matrix. I will provide a review of this concept and shall illustrate how experimental access to the Wigner-Smith operator enables wave-front shaping protocols at the optimal level of efficiency.
Date:
Seminars
16
February, 2020
Sunday
Hour: 13:15

Shaping liquid droplets and elastic membranes

Zvonimir Dogic
We describe two self-assembly pathways observed in micron-thick colloidal membranes that spontaneously assemble in mixtures of monodisperse colloidal rods and non-adsorbing polymer. In a first example, we study mechanisms by which membrane-embedded 2D liquid droplets acquire unusual non-spherical shapes, suggesting that the interfacial edge domain has spontaneous non-zero edge curvature. These experimental observations can be explained by a simple geometric argument which predicts that the edge curvature towards shorter rod domains softens the resistance of the edge to twist. In a second example, we study the 3D structure of membranes composed of miscible rod-like molecules of differing lengths. Above a critical concentration of shorter rods flat 2D membranes become unstable and assume a bewildering variety of different shapes and topologies. Simple arguments suggest that doping colloidal membranes with miscible shorter rods tunes the membrane’s Gaussian modulus, which in turn destabilizes flat 2D membranes.
Date:
Colloquia
13
February, 2020
Thursday
Hour: 11:15-12:30

Highly magnified gravitationally lensed stars as a probe to the nature of dark matter

Jordi Miralda-Escude
Dark matter continues to pose one of the most important questions in modern cosmology. Gravitationally lensed multiple images of galaxies, quasars and stars provide several opportunities for testing the clumpiness of dark matter on small scales due to, for example, compact objects, axion mini-clusters and waves, or subhalos orbiting on galactic or cluster dark matter halos. The idea of using highly magnified stars by lensing clusters to probe this small-scale granularity in the dark matter will be discussed.
Date:
Seminars
12
February, 2020
Wednesday
Hour: 11:00

Optics, Vision, and Evolution, after Mitchell Feigenbaum 1944-2019

Jean-Pierre Eckmann
Many people are aware of Feigenbaum's astonishing discovery of the universality of period doubling, and the constant delta=4.66920 which carries his name. In the last 13 years of his life Feigenbaum worked on other subjects, and he wrote the manuscript (in TeX) of a book whose title is "Reflections on a Tube". This is closely related to his life-long interest in optics and aspects of vision. It deals with the optics of images reflected in a cylindrical mirror (usually called anamorphic pictures). He shows that the eye does not interpret ray-tracing, but caustics. But there are two caustics, and therefore, the viewer can actually see two different images. The visual system will often prefer one over the other. The question is the "which" and "why"? Starting from this discovery, Feigenbaum derived other aspects of this observation, dealing with the vision of fish, the "broken" pencil in water, or aspects of the floor of swimming pools. All these examples show two possible images. His study tells me how a simple study in classical optics can lead to interesting questions in perception and the visual system. I will give an overview of this project. As I discussed with him, over those 13 years, many aspects of his work, I have edited his manuscript so it can be published as a book which should appear in a forseeable future.
Date:
Seminars
10
February, 2020
Monday
Hour: 14:15

Thermal conductance of one dimensional disordered harmonic chains

Biswarup Ash - WIS
Department of Physics of Complex Systems
Heat transfer in solids is usually described in terms of Fourier's law according to which the thermal conductance of a material scales inversely with its length or, equivalently, thermal conductivity is independent of sample length. Theoretical and experimental studies over the past decade have demonstrated that Fourier's law is violated for a variety of one-dimensional systems. Despite the large number of studies of many intriguing models, the validity criteria for Fourier's law remain elusive, and a breakdown of Fouriers law seems to be commonplace. In this talk, I will discus heat conduction mediated by longitudinal phonons in one dimensional disordered harmonic chains to understand the role of different parameters that may affect the scaling of thermal conductance in these systems. Using scaling properties of the phonon density of states and localization in disordered systems, we find non-trivial scaling of the thermal conductance with the system size. Our theoretical findings are corroborated by extensive numerical analysis. We show that, suprisingly, the thermal conductance of a system with strong disorder, characterized by a `heavy-tailed' probability distribution, and with large impedance mismatch between the bath and the system scales normally with the system size, i.e., in a manner consistent with Fourier's law. We identify a dimensionless scaling parameter, related to the temperature scale and the localization length of the phonons, through which the thermal conductance for different models of disorder and different temperatures follows a universal behavior.
Date:
Seminars
09
February, 2020
Sunday
Hour: 13:15

Packets of Diffusing Particles Exhibit Universal Exponential Tails

Stas Burov
Department of Physics of Complex Systems
Brownian motion is a Gaussian process described by the central limit theorem. However, exponential decays of the positional probability density function $P(X,t)$ of packets of spreading random walkers, were observed in numerous situations that include glasses, live cells and bacteria suspensions. We show that such exponential behavior is generally valid in a large class of problems of transport in random media. By extending the Large Deviations approach for a continuous time random walk we uncover a general universal behavior for the decay of the density. It is found that fluctuations in the number of steps of the random walker, performed at finite time, lead to exponential decay (with logarithmic corrections) of $P(X,t)$. This universal behavior holds also for short times, a fact that makes experimental observations readily achievable.
Date:
Seminars
09
February, 2020
Sunday
Hour: 13:15

Packets of Diffusing Particles Exhibit Universal Exponential Tails

Stas Burov, Bar-Ilan University
Brownian motion is a Gaussian process described by the central limit theorem. However, exponential decays of the positional probability density function $P(X,t)$ of packets of spreading random walkers, were observed in numerous situations that include glasses, live cells and bacteria suspensions. We show that such exponential behavior is generally valid in a large class of problems of transport in random media. By extending the Large Deviations approach for a continuous time random walk we uncover a general universal behavior for the decay of the density. It is found that fluctuations in the number of steps of the random walker, performed at finite time, lead to exponential decay (with logarithmic corrections) of P(X,t). This universal behavior holds also for short times, a fact that makes experimental observations readily achievable.
Date:
Colloquia
06
February, 2020
Thursday
Hour: 11:15-12:30

Testing Gravity with Cold Atoms

Guglielmo M. Tino
The ability to control the quantum degrees of freedom of atoms using laser light opened the way to precision measurements of fundamental physical quantities. I will describe experiments for precision tests of gravitational physics using new quantum devices based on ultracold atoms, namely, atom interferometers and optical clocks. I will report on the measurement of the gravitational constant G with a Rb Raman interferometer, on experiments based on Bloch oscillations of Sr atoms confined in an optical lattice for gravity measurements at small spatial scales, and on new tests of the Einstein equivalence principle. I will also discuss prospects to use atoms as new detectors for gravitational waves and for experiments in space.
Date:
Colloquia
30
January, 2020
Thursday
Hour: 11:15-12:45

Scale Invariance at low accelerations as an alternative to the dark Universe

Mordehai Milgrom
Galactic systems and the Universe at large exhibit significant anomalies when analyzed within Newtonian dynamics and general relativity: Large discrepancies are found between the gravitational masses required by the observed dynamics, and the masses we actually observe in these systems. The mainstream explanation of these anomalies invokes the dominant and ubiquitous presence of “dark matter”. The "MOND" paradigm suggests, instead, that the discrepancies are due to breakdown of standard dynamics in the limit of low accelerations, where MOND dynamics are space-time scale invariant. MOND accounts for many detailed manifestations of the mass discrepancies with no need for dark matter. I will outline the paradigm, some of its achievements, and some remaining problems and desiderata.
Date:
Seminars
27
January, 2020
Monday
Hour: 14:15

The Surprises of a Nanochannel –

Yoav Green
Department of Physics of Complex Systems
Nanofluidic systems have the potential to revolutionize numerous fields of high practical importance, including desalination, energy harvesting, bio-sensing, fluid based electrical circuits, and more. It is, therefore, not surprising that in the last two decades we are witnessing an increase in nanofluidic-based research. However, realizing the full potential of nanofluidics remains conditional to conquering several significant challenges. Notably, our current understanding of the fundamental physical phenomena that govern ion transport through nanochannels is incomplete and many key questions remain open. Fifteen years ago it was suggested that low-voltage Ohmic response of nanochannel-microchannels systems was dominated by the electrical resistance of the nanochannel, and that the resistances of the adjacent microchannels, were negligible. I will present evidence contradicting this suggestion that has since become paradigm. I will present a new modified paradigm which emphasizes the importance of the microchannels in determining the overall response. Our result suggest the need to conduct fundamental driven research to further reveal the physics of ion-transport at low-voltages so that we can unveil the physics at high-voltages where non-linear electroconvective effects are prevalent. Bio: Yoav Green is currently a senior lecturer in the Department of Mechanical Engineering at Ben-Gurion University. Before that, Yoav was post-doctoral researcher in the Harvard T. H. Chan School of Public Health where he worked in the field of biomechanics. Yoav holds a PhD in mechanical engineering from the Technion - Israel Institute of Technology where his research fields were nanofluidics and electrokinetics. Yoav also holds an MSc in physics (astrophysics and astronomy) from the Weizmann Institute of Science, and BSc in aerospace engineering from the Technion.
Date:
Colloquia
23
January, 2020
Thursday
Hour: 11:15-12:30

Growing Droplets in Cells and Gels

Eric Dufresne
To function effectively, living cells compartmentalize myriad chemical reactions. In the classic view, distinct functional volumes are separated by thin oily-barriers called membranes. Recently, the spontaneous sorting of cellular components into membraneless liquid-like domains has been appreciated as an alternate route to compartmentalization. I will review the essential physical concepts thought to underly these biological phenomena, and outline some fundamental questions in soft matter physics that they inspire. Then, I will focus on the coupling of phase separation to elastic stresses in polymer networks. Using a series of experiments spanning living cells and synthetic materials, I will demonstrate that bulk mechanical stresses dramatically impact every stage in the life of a droplet, from nucleation and growth to ripening and dissolution. These physical phenomena suggest new mechanisms that cells could exploit to regulate phase separation, and open new routes to the assembly of functional materials
Date:
Seminars
20
January, 2020
Monday
Hour: 14:15

Self-assembled Electrolytes: Conserved media with non-equilibrium properties and why should we care about it?

Arik Yochelis, BGU
Department of Physics of Complex Systems
Self-assembly driven by phase separation coupled to Coulombic interactions is fundamental to a wide range of applications, examples of which include soft matter lithography via di-block copolymers, membrane design using poly-electrolytes, and renewable energy applications based on complex nano-materials, such as ionic liquids. I will show by using two continuum case models, ionic liquids and charged polymers, that although self-assembly in electrolytes is a gradient flow system, it surprisingly displays several fundamental features that are related to far from equilibrium (reaction-diffusion) systems and thus, allow for novel realizations, interpretations, and applications to concentrated electrolytes.
Date:
Seminars
19
January, 2020
Sunday
Hour: 13:15

The reference map technique for simulating complex materials and

Christopher Rycroft
Department of Physics of Complex Systems
> Conventional computational methods often create a dilemma for fluid–structure interaction problems. Typically, solids are simulated using a Lagrangian approach with grid that moves with the material, whereas fluids are simulated using an Eulerian approach with a fixed spatial grid, requiring some type of interfacial coupling between the two different perspectives. Here, a fully Eulerian method for simulating structures immersed in a fluid will be presented. By introducing a reference map variable to model finite-deformation constitutive relations in the structures on the same grid as the fluid, the interfacial coupling problem is highly simplified. The method is particularly well suited for simulating soft, highly-deformable materials and many-body contact problems, and several examples will be presented. This is joint work with Ken Kamrin (MIT).
Date:
Colloquia
16
January, 2020
Thursday
Hour: 11:15-12:30

The three jewels in the crown of the LHC

Yossi Nir
The ATLAS and CMS experiments have made three major discoveries: The discovery of an elementary spin-zero particle, the discovery of the mechanism that makes the weak interactions short-range, and the discovery of the mechanism that gives the third generation fermions their masses. I explain how this progress in our understanding of the basic laws of Nature was achieved.
Date:
Seminars
13
January, 2020
Monday
Hour: 14:15

Full counting and extreme value statistics for a gas of 2d charged particles

Bertrand Lacrois-A-Chez-Toine
Department of Physics of Complex Systems
In this talk, we consider a model of 2d one component plasma, i.e. a gas of identical negatively charged particles. These charges are at equilibrium at inverse temperature B in an external containing potential created by a positive charge smeared over the two dimensional plane. For specific potentials and temperatures, this problem is connected to the study of eigenvalues of non-Hermitian random matrices, to the quantum fluctuations of fermions in a rotating harmonic trap or in a Laughlin state. We study the extreme value statistics for this system as well as the full counting statistics, i.e. the number of charges in a given domain of space. For both these observables, the regime of typical fluctuations [1] and the large deviation regime [2, 3] have been characterized. While one would naively expect a smooth matching between these regimes, as it is the case for example for observables of Hermitian random matrices, it is not the case here. We solve this puzzle by showing that for both cases, an intermediate regime" of fluctuations emerges and characterize it in detail [4, 5]. This regime is universal with respect to a large class of confining potential. We have also considered potentials that do not enter this class and shown that there are cases where an intermediate regime of fluctuation does not appear. References [1] T. Shirai, J. Stat. Phys. 123, 615 (2006). [2] R. Allez, J. Touboul, G. Wainrib, J. Phys. A: Math. Theor. 47, 042001 (2014). [3] F. D. Cunden, F. Mezzadri, P. Vivo, J. Stat. Phys. 164, 1062 (2016). [4] B. Lacroix-A-Chez-Toine, A. Grabsch, S. N. Majumdar, G. Schehr, J. Stat. Mech.: Theory Exp. 013203 (2018).
Date:
Colloquia
09
January, 2020
Thursday
Hour: 11:15-12:30

Gravity, entanglement, and bit threads

Matthew Headrick
In trying to understand quantum gravity at a fundamental level, one of the most confusing questions is where the degrees of freedom are. So-called holographic dualities help with this question, by showing that certain quantum gravity theories are equivalent to conventional quantum field theories, in which we understand in principle where the degrees of freedom are and how they interact. Using such dualities, a new way of understanding entanglement in quantum gravity, involving so-called “bit threads”, has recently been developed. From this point of view, space becomes a channel for carrying entanglement of fundamental degrees of freedom. We will explain what holographic dualities are, what bit threads are, and what they might tell us about the nature of space in quantum gravity.
Date:
Seminars
06
January, 2020
Monday
Hour: 14:15

Adaptation of bacteria with CRISPR and adaptation on a rugged fitness landscape

Marija Vucelja
Department of Physics of Complex Systems
I will tell you two stories of adaptation of populations aided and enriched by statistical physics approaches. The first story is about the adaptation of bacteria with CRISPR. CRISPR-Cas is a famous biology buzz word, due to its applications to gene editing. However, CRISPR-Cas is also a prokaryote immune system. It works as a “library” of previous infections. This library contains snippets of exogenous genetic material. With a new infection, the library is consulted, and if a match is found, the attempt will be made to neutralize the intruding genome. Bacteria use CRISPR-Cas as an immune system against phages and plasmids. Such immunity is hereditary and dynamic — it can be gained and lost during the lifetime of the single bacteria. Also, the process of acquiring snippets when exposed to the same phage is stochastic, and the same strain bacteria in a population contain different CRISPR loci content and thus variable immunity to the phage. We use dynamical systems approaches to predict the shape of this diverse distribution of CRISPR loci content within a bacterial population as a function of two crucial parameters — the rate of acquisition and the immunity to the phage. The second story is about adaptation on a rugged fitness landscape. A crude measure of adaption to a new environment called fitness. Often one defines fitness as the expected growth rate. The higher the fitness, the more thriving is a population. What happens over long times for a population with a finite genome — when all beneficial, fitness mutations, are exhausted? Contrary to expectations, the experiments show that fitness does not reach a plateau. Here we introduce a spin-glass microscopic model, where a genome can be represented as a spin configuration, and individual spins are genes. The fitness plays the role of minus the Hamiltonian of the system. We use numerical approaches and estimates to study hopping between metastable states on a rugged fitness landscape. We show that with gene interactions (interacting spins), double beneficial mutations (flipping of pairs of spins) can lead to a slow, logarithmic increase of fitness in a wide class of cases.
Date:
Seminars
06
January, 2020
Monday
Hour: 14:15

Adaptation of bacteria with CRISPR and adaptation on a rugged fitness landscape

Marija Vucelja
Department of Physics of Complex Systems
I will tell you two stories of adaptation of populations aided and enriched by statistical physics approaches. The first story is about the adaptation of bacteria with CRISPR. CRISPR-Cas is a famous biology buzz word, due to its applications to gene editing. However, CRISPR-Cas is also a prokaryote immune system. It works as a “library” of previous infections. This library contains snippets of exogenous genetic material. With a new infection, the library is consulted, and if a match is found, the attempt will be made to neutralize the intruding genome. Bacteria use CRISPR-Cas as an immune system against phages and plasmids. Such immunity is hereditary and dynamic — it can be gained and lost during the lifetime of the single bacteria. Also, the process of acquiring snippets when exposed to the same phage is stochastic, and the same strain bacteria in a population contain different CRISPR loci content and thus variable immunity to the phage. We use dynamical systems approaches to predict the shape of this diverse distribution of CRISPR loci content within a bacterial population as a function of two crucial parameters — the rate of acquisition and the immunity to the phage. The second story is about adaptation on a rugged fitness landscape. A crude measure of adaption to a new environment called fitness. Often one defines fitness as the expected growth rate. The higher the fitness, the more thriving is a population. What happens over long times for a population with a finite genome — when all beneficial, fitness mutations, are exhausted? Contrary to expectations, the experiments show that fitness does not reach a plateau. Here we introduce a spin-glass microscopic model, where a genome can be represented as a spin configuration, and individual spins are genes. The fitness plays the role of minus the Hamiltonian of the system. We use numerical approaches and estimates to study hopping between metastable states on a rugged fitness landscape. We show that with gene interactions (interacting spins), double beneficial mutations (flipping of pairs of spins) can lead to a slow, logarithmic increase of fitness in a wide class of cases.
Date:
Colloquia
02
January, 2020
Thursday
Hour: 11:15-12:30

Pulling Yourself by your Bootstraps in Quantum Field Theory

Leonardo Rastelli
Quantum field theory (QFT) is the universal language of theoretical physics, underlying the Standard Model of elementary particles, the physics of the early Universe and a host of condensed matter phenomena such as phase transitions and superconductivity. A great achievement of 20th-century physics was the understanding of weakly coupled quantum field theories where interactions can be treated as small perturbations of otherwise freely moving particles. Critical challenges for the 21st century include solving the problem of strong coupling and mapping the whole space of consistent QFTs. In this lecture, I will overview the bootstrap approach, the idea that theory space can be determined from the general principles of symmetry and quantum mechanics. This strategy provides a new unifying language for QFT and has allowed researchers to make predictions for physical observables even in strongly coupled theories. By holographic duality, the bootstrap program has also implications for the space of consistent quantum gravity theories.
Date:
Seminars
30
December, 2019
Monday
Hour: 14:15

Physical Genomics Harnessing physics and chemistry for single-molecule analysis of the human genome

Yuval Ebenstein, TAU
Department of Physics of Complex Systems
DNA is an amazing memory device that holds the operating system of life. However, DNA sequencing fails to extract the full range of information associated with genetic material and is lacking in its ability to resolve variations between genomes. As a consequence, many genomic features remain poorly characterized in the human genome reference. In addition, the information content of the genome extends beyond the base sequence in the form of chemical modifications such as DNA methylation or DNA damage lesions that chemically encode our life experiences in our DNA. By applying experimental principles of single molecule detection we gain access to the structural variation and long range patterns of genetic and epigenetic information. We show how physical extension of long DNA molecules on surfaces and in nanofluidic channels reveals such information in the form of a linear, optical “barcode” showing distinct types of observables. Recent results from our lab demonstrate our ability to detect epigenetic marks and various forms of DNA damage on individual genomic DNA molecules and use this information for medical diagnostics.
Date:
Colloquia
26
December, 2019
Thursday
Hour: 11:15-12:30

The Large Synoptic Survey Telescope: Status Update and Prospects for Science

Steven M. Kahn
The Large Synoptic Survey Telescope (LSST) is a large-aperture, wide-field ground-based telescope designed to provide a time-domain imaging survey of the entire southern hemisphere of sky in six optical colors (ugrizy). Over ten years, LSST will obtain ~ 1,000 exposures of every part of the southern sky, enabling a wide-variety of distinct scientific investigations, ranging from studies of small moving bodies in the solar system, to constraints on the structure and evolution of the Universe as a whole. The development of LSST is a collaboration between the US National Science Foundation, which is supporting the development of the telescope and data system, and the US Department of Energy, which is supporting the development of the 3.2 gigapixel camera, the largest digital camera ever fabricated for astronomy. Approved in 2014, LSST is now well into construction, and is on track to beginning operations in 2022. I will review the design and technical status of the Project, and provide an overview of some of the exciting science highlights that we expect to come from this facility.
Date:
Seminars
23
December, 2019
Monday
Hour: 14:15

New directions for diffusive processes: defect formation through a nonequilibrium phase transition, open quantum systems and uncertainty relations in mesoscopic systems

Ohad Shpielberg
Department of Physics of Complex Systems
The macroscopic fluctuation theory gives an efficient hydrodynamic description for classical nonequilibrium diffusive systems. In this talk, we would cover how it can be applied and generalised in three directions: a. Towards a theory for open quantum diffusive systems, comparable to the macroscopic fluctuation theory. b. Defect formation as a system is (slowly) driven in time through a continuous phase transition can be described by a scaling theory - the Kibble-Zurek Mechanism. The macroscopic fluctuation theory allows to explore the exact evolution of defects for a large set of cases. Thus, we are in a position to go beyond the scaling arguments of the Kibble-Zurek Mechanism. c. The recently discovered thermodynamic uncertainty relations define a transport efficiency in thermal systems showing that the mean current, current fluctuations and dissipation are intimately linked. Here we will briefly show how this idea can be extended to (athermal) mesoscopic coherent processes.
Date:
Colloquia
19
December, 2019
Thursday
Hour: 11:15-12:30

Overcoming resolution limits with quantum sensing by utilising error correction

Alex Ratzker
Quantum sensing and metrology exploit quantum aspects of individual and complex systems to measure a physical quantity. Quantum sensing targets a broad spectrum of physical quantities, of both static and time-dependent types. While the most important characteristic for static quantities is sensitivity, for time-dependent signals it is the resolution, i.e. the ability to resolve two different frequencies. The decay time of the probe imposes a fundamental limit on the quantum sensing efficiency. While error correction methods can prolong this time it was not clear if such a procedure could be used in a quantum sensing protocol. In this talk I will present a study of spectral resolution problems with quantum sensors, and the development of a new super-resolution method that relies on quantum features for which the limitation imposed by the finite decay time can be partially overcome by error correction.
Date:
Colloquia
12
December, 2019
Thursday
Hour: 11:15-12:30

Magic Angle Bilayer Graphene - Superconductors, Orbital Magnets, Correlated States and beyond

Dmitri K. Efetov
When twisted close to a magic relative orientation angle near 1 degree, bilayer graphene has flat moire superlattice minibands that have emerged as a rich and highly tunable source of strong correlation physics, notably the appearance of superconductivity close to interaction-induced insulating states. Here we report on the fabrication of bilayer graphene devices with exceptionally uniform twist angles. We show that the reduction in twist angle disorder reveals insulating states at all integer occupancies of the four-fold spin/valley degenerate flat conduction and valence bands, i.e. at moire band filling factors nu = 0, +(-) 1, +(-) 2, +(-) 3, and reveals new superconductivity regions below critical temperatures as high as 3 K close to - 2 filling. In addition we find novel orbital magnetic states with non-zero Chern numbers. Our study shows that symmetry-broken states, interaction driven insulators, and superconducting domes are common across the entire moire flat bands, including near charge neutrality. We further will discuss recent experiments including screened interactions, fragile topology and the first applications of this amazing new materials platform.
Date:
Seminars
09
December, 2019
Monday
Hour: 14:15

A quantitative footprint of irreversibility in the absence of observable currents

Gili Bisker
Department of Physics of Complex Systems
Time irreversibility is the hallmark of nonequilibrium dissipative processes. Detecting dissipation is essential for our basic understanding of the underlying physical mechanism, however, it remains a challenge in the absence of observable directed motion, flows, or fluxes. Additional difficulty arises in complex systems where many internal degrees of freedom are inaccessible to an external observer. In living systems, for example, the dissipation is directly related to the hydrolysis of fuel molecules such as adenosine triphosphate (ATP), whose consumption rate is difficult to directly measure in many experimental setups. In this talk, I will introduce a novel approach to detect time irreversibility and estimate the entropy production from time-series measurements, even in the absence of observable currents. This method can be implemented in scenarios where only partial information is available and thus provides a new tool for studying nonequilibrium phenomena. 1. G. Bisker et al. Inferring broken detailed balance in the absence of observable currents, Nature Communications, 10(1), 1-10 (2019) 2. G. Bisker et al. Hierarchical Bounds on Entropy Production Inferred from Partial Information, Journal of Statistical Mechanics: Theory and Experiment (9), 093210 (2017)
Date:
Seminars
08
December, 2019
Sunday
Hour: 13:15

Representation, inference and design of multicellular systems

Nitzan Mor
The past decade has witnessed the emergence of single-cell technologies that measure the expression level of genes at a single-cell resolution. These developments have revolutionized our understanding of the rich heterogeneity, structure, and dynamics of cellular populations, by probing the states of millions of cells, and their change under different conditions or over time. However, in standard experiments, information about the spatial context of cells, along with additional layers of information they encode about their location along dynamic processes (e.g. cell cycle or differentiation trajectories), is either lost or not explicitly accessible. This poses a fundamental problem for elucidating collective tissue function and mechanisms of cell-to-cell communication. In this talk I will present computational approaches for addressing these challenges, by learning interpretable representations of structure, context and design principles for multicellular systems from single-cell information. I will first describe how the locations of cells in their tissue of origin and the resulting spatial gene expression can be probabilistically inferred from single-cell information by a generalized optimal-transport optimization framework that can flexibly incorporate prior biological assumptions or knowledge derived from experiments. Inference in this case is based on an organization principle for spatial gene expression, namely a structural correspondence between distances of cells in expression and physical space, which we hypothesized and supported for different tissues. We used this framework to spatially reconstruct diverse tissues and organisms, including the fly embryo, mammalian intestinal epithelium and cerebellum, and further inferred spatially informative genes. Since cells encode multiple layers of information, in addition to their spatial context, I will also discuss several approaches for the disentanglement of single-cell gene expression into distinct biological processes, based on ideas rooted in random matrix theory and manifold learning. I will finally discuss how these results can be generalized to reveal principles underlying self-organization of cells into multicellular structures, setting the foundation for the computationally-directed design of cell-to-cell interactions optimized for specific tissue structure or function. Sunday, December 8, 2019 at 13:00 Sandwiches at 12:45 Drory Auditorium
Date:
Colloquia
05
December, 2019
Thursday
Hour: 11:15-12:30

What Processes Shape the Disks of Galaxies?

Hans-Walter Rix
The Milky Way, as a very average spiral galaxy, can serve as a galaxy model organism to tell us which physical processes shape the current structure and stellar content of galaxies: what sets the overall radial profile of the disk, which the present-day orbital of any star, and how much formation memory does the Milky Way's disk retain? We can now draw on global Galactic stellar surveys that constrain orbits, abundances and ages. I will show how modelling these data now shows that global radial orbit migration is a very strong effect that decisively shapes the structure of the Milky Way's disk. If the Milky Way is typical in this respect this explains why galaxy disk profiles are exponential. And I will also sketch how data from the Gaia mission can now tell us in far more detail the mechanisms that drive orbit evolution throughout our disk.
Date:
Seminars
01
December, 2019
Sunday
Hour: 13:15

Active Matter: `active thermodynamics’ and the dynamics of biopolymer gels

Tomer Markovich
Department of Physics of Complex Systems
Active materials are composed of many components that can convert energy from its environment (usually in the form of chemical energy) into directed mechanical motion. Time reversal symmetry is thus locally broken, leading to a variety of novel phenomena such as motility induced phase separation, reversal of the Ostwald process and flocking. Examples of active matter are abundant and range from living matter such as bacteria, actomyosin networks and bird flocks to Janus particles, colloidal rollers and macroscale driven chiral rods. Nevertheless, in many cases experiments on active materials exhibit equilibrium like properties (e.g., sedimentation of bacteria). In the first part of the talk I will try to answer the important question: how do we know a system is `active’? And if it is, can we have generic observables as in equilibrium thermodynamics? Can we measure how far it is from equilibrium? In the second part of the talk I will focus on examples of activity in biopolymer gels, such as the cytoskeleton of living cells. I will show some of the effects of active motors with emphasis on chiral motors. The latter does not have a unique hydrodynamic description, which one can utilize to gain access to the microscopic details of the complex motors using macroscopic measurements. I will also discuss non-motor activity and demonstrate how it can result in contractility, e.g., in the process of cell division.
Date:
Colloquia
28
November, 2019
Thursday
Hour: 11:15-12:30

Attosecond Interferometry

Nirit Dudovich
Attosecond science is a young field of research that has rapidly evolved over the past decade. The progress in this field opened a door into a new area of research that allows one to observe multi-electron dynamics in atoms, molecules and solids. One of the most important aspect of attosecond spectroscopy lies in its coherent nature. Resolving the internal coherence is a primary challenge in this field, serving as a key step in our ability to reconstruct the internal dynamics. As in many other branches in physics, coherence is resolved via interferometry. In this talk, I will describe advanced schemes for attosecond interferometry. The application of these schemes provides direct insights into a range of fundamental phenomena in nature, from tunneling and photoionization in atomic systems to ultrafast chiral phenomena in molecules.
Date:
Colloquia
21
November, 2019
Thursday
Hour: 11:15-12:30

Quantum Many-Body Integrability, Solvability, and Chaos

Vladimir Rosenhaus
This talk is concerned with the question: How can we characterize, find, and solve quantum field theories and many-body systems that exhibit features of quantum chaos? We describe the recently discovered Sachdev-Ye-Kitaev model: a quantum mechanical system of a large number of fermions with all-to-all quartic, Gaussian-random, interactions that, remarkably, is chaotic, nearly conformally invariant, and solvable. We contrast this with integrable two-dimensional quantum field theories, such as the Sine-Gordon model. We end with some comments on hopes for a framework to find nearly integrable quantum field theories that are nearly solvable.
Date:
Seminars
20
November, 2019
Wednesday
Hour: 09:00-17:00

STATISTICAL DYNAMICS DAY XI

Department of Physics of Complex Systems
09:40 – 10:00 Yoav Sagi - Technion “The attractive Fermi polaron problem - experimental study with an ultracold Fermi gas” 10:00 – 10:20 David Kessler – Bar-Ilan University “Quantum First-Detection Problems” 10:20 – 10:40 Dekel Shapira – Ben-Gurion University “Interplay of Quantum and stochastic transport along chains“ 10:40 – 11:00 Bertrand Lacroix – Weizmann Institute "Universal intermediate deviation functions for the 2d One Component Plasma” Coffee Break 11:30 – 11:50 Erez Braun - Technion “Is morphogenesis in animal development reversible?” 11:50 – 12:10 Yasmine Meroz – Tel-Aviv University “Form and Function: Emergent Structures in Growth-Driven Systems” 12:10 – 12:30 Ehud Meron – Ben-Gurion University “Dynamics of desertification fronts” 12:30 – 12:50 Iddo Eliazar – Tel-Aviv University “Max-Min/Min-Max of random matrices” Lunch 14:00 – 14:20 Ofer Biham – Hebrew University “Convergence of contracting networks towards an asymptotic maximum-entropy structure” 14:20 – 14:40 Asaf Miron – Weizmann Institute “Phase transition in transport though a narrow-channel” 14:40 – 15:00 Gianluca Teza – Weizmann Institute “Memory leaves entropy production fluctuations invariant under coarse-graining” Coffee Break 15:20 – 15:40 Hillel Aharoni – Weizmann Institute “Universal Inverse Design of Nematic Elastomer Surfaces”. 15:40 – 16:00 Michael Moshe – Hebrew University “Mechanical Meta-Materials as lattices of quadrupolar elastic charges” 16:00 – 16:20 Naomi Oppenheimer – Tel-Aviv University “Hurricane dynamics in a membrane"
Date:
Colloquia
14
November, 2019
Thursday
Hour: 11:15-12:30

ESO's Extremely Large Telescope

Jason Spyromilio
The 39-m ELT is under construction by the European Southern Observatory. When completed it will be the largest optical/NIR telescope in the world at one of the best sites. The talk shall focus on the challenges associated with building this telescope and will describe the first generation instrumentation complement and science drivers.
Date:
Colloquia
07
November, 2019
Thursday
Hour: 11:15-12:30

A new attempt to solve the type Ia supernova problem

Boaz Katz
Supernovae distribute most of the chemical elements that we are made of and are detected daily, yet we still do not know how they explode. Type Ia supernovae consist of most recorded supernovae and are likely the result of thermonuclear explosions of white dwarfs (common compact stars with mass similar to the sun and radius similar to earth), but what mechanism causes about 1% of white dwarfs to ignite remains unknown. I will describe our ongoing recent attempt to solve this puzzle that involves a new potential answer - direct collisions of white dwarfs in multiple stellar systems, new robust tools to compare explosion models to observations - in particular the use of global conservation of energy in emitted radiation, and new key observations - in particular late-time spectra of ~100 recent supernovae.
Date:
Colloquia
18
July, 2019
Thursday
Hour: 11:15-12:30

Special Physics Colloquium

Dr. Osip Schwartz
Laser manipulation of quantum particles, such as atoms, ions, and molecules, underpins much of modern physics. Electrons, too, can be coherently controlled by light. In this work, we study electron-laser interaction in free space and find that the conventional description based on the effective (ponderomotive) potential requires significant modification. We demonstrate laser-based phase manipulation of the electron wave function by performing interferometric experiments in a transmission electron microscope (TEM) and capture TEM images of the light wave. We then utilize the laser-induced phase shift to realize a nearly ideal phase plate for Zernike phase contrast TEM, solving a long-standing problem and addressing the challenge of dose-efficient interrogation of radiation-sensitive specimens. The laser phase plate is widely expected to advance the TEM studies of protein structure and cell organization.
Date:
Seminars
27
June, 2019
Thursday
Hour: 11:15-12:30

special faculty seminar

Prof. Roee Ozeri
In this seminar I’ll review the rationale behind, and the essence of, the redefinition of the standard international systems of units that happened on May 20th 2019. I’ll review some of the possible experiments with which standard units can be realized for empirical references. .
Date:
Colloquia
20
June, 2019
Thursday
Hour: 11:15-12:30

Physics Colloquium

Ranny Budnik
The hunt for Dark Matter is reaching at a crossroads - after two decades of incredible pace, where five orders of magnitude in parameter space were covered, no unambiguous signal has emerged for interaction between the alleged particles and our normal, baryonic matter. The next generation detectors, aiming at another order of magnitude sensitivity increase, are on the runway, and the question of what will be next takes interesting turns. I will cover the evidence for the existence of Dark Matter, present the state of the art results from the XENON1T experiment, and play with some novel ideas for the next step, trying to move the lamppost to where Dark Matter may still stay hidden.
Date:
Colloquia
06
June, 2019
Thursday
Hour: 11:15-12:30

Neutrinos as the key to the universe as we know it

Prof. Yuval Grossman
There are three open questions in physics which seem unrelated: Why is there only matter around us? How neutrinos acquire their tiny masses? Why all particles in Nature have integer electric charges? It turns out that these open questions are related. In the talk I will explain these open questions, the connection between them, and describe the on-going theoretical and experimental efforts in understanding them.
Date:
Colloquia
29
May, 2019
Wednesday
Hour: 11:15-12:30

Vortices in superconducting arrays: probing dissipation and interactions

Prof. Nadya Mason
Superconductivity continues to be an exciting and fertile field of research, with potential applications in energy efficiency and storage. Non-superconducting systems in contact with superconductors have been of particular recent interest, as these proximity-coupled superconductors may show new behaviors or harbor unusual excitations (eg, Majoranas in topological-superconductor systems). A key to understanding and utilizing superconductors is understanding their behavior in magnetic fields, particularly when the field penetrates as quantized tubules of flux, or vortices. In this talk I will show that, although vortices have been studied for many years, measurements of their current-driven dynamics can still lead to new results and understanding. I will discuss transport measurements of current-driven vortices in superconductor-normal-superconductor (SNS) arrays, where we are able to access a number of vortex regimes, and find unusual behavior in the non-equilibrium transitions between vortex states. First, in the low magnetic field regime, we find that the dynamic behavior of vortices is consistent with the presence of time delayed dissipative forces. I will also discuss how at higher magnetic fields, vortex de-pinning occurs in two steps, consistent with a commensurate lattice appearing even for non-commensurate magnetic field values. This two-step behavior is due to strong vortex interactions, and has not previously been observed. Finally, I will discuss measurements of vortex arrays on topological insulators, where we see enhanced dissipation and evidence of unusual charged vortices, predicted as the “Witten effect” in topological systems.
Date:
Colloquia
16
May, 2019
Thursday
Hour: 11:15-12:30

A New Spin On Superconductivity

Prof. Amir Yacoby
Mesoscopic physics, pioneered by Joe Imry nearly 4 decades ago, explores the behavior of matter on length scales where dimensionality, coherence, and interactions compete to produce material properties that are fundamentally different from their bulk counterparts. For example, the conventional wisdom of superconductivity, developed in 1957 by Bardeen, Cooper and Schrieffer (BCS) describes this state in terms of a condensate of electron pairs arranged in a spatially isotropic wave function with no net momentum or angular momentum (a spin-singlet configuration). However, on mesoscopic length scales entirely different types of superconductivity may be realized such as unconventional pairing where electrons are arranged in triplet rather than singlet configurations. Such superconductors may enable dissipationless transport of spin and may also give rise to elementary excitations that do not obey the conventional Fermi or Bose statistics but rather have non-Abelian statistics where the exchange of two particles transforms the state of the system into a new quantum mechanical state. In this talk I will describe some of our recent work that explores the proximity effect between a conventional superconductor and a semiconductor with strong spin-orbit interaction. Using supercurrent interference, we show that we can tune the induced superconductivity continuously from conventional to unconventional, that is from singlet to triplet. Our results open up new possibilities for exploring unconventional superconductivity as well as provide an exciting new pathway for exploring non-Abelian excitation.
Date:
Seminars
01
May, 2019
Wednesday
Hour: 11:00-12:00

Excitons in Flatland: Exploring and Manipulating Many-body Effects on the Optical Excitations in Quasi-2D Materials


Dr. Diana Qiu
Since the isolation of graphene in 2004, atomically-thin quasi-two-dimensional (quasi-2D) materials have proven to be an exciting platform for both applications in novel devices and exploring fundamental phenomena arising in low dimensions. This interesting low-dimensional behavior is a consequence of the combined effects of quantum confinement and stronger electron-electron correlations due to reduced screening. In this talk, I will discuss how the optical excitations (excitons) in quasi-2D materials, such as monolayer transition metal dichalcogenides and few-layer black phosphorus, differ from typical bulk materials. In particular, quasi-2D materials are host to a wide-variety of strongly-bound excitons with unusual excitation spectra and massless dispersion. The presence of these excitons can greatly enhance both linear and nonlinear response compared to bulk materials, making them ideal candidates for optoelectronics and energy applications. Moreover, due to enhanced correlations and environmental sensitivity, the electronic and optical properties of these materials can be easily tuned. I will discuss how substrate engineering, stacking of different layers, and the introduction or removal of defects can be used to tune the band gaps and optical selection rules in quasi-2D materials.
Date:
Colloquia
01
May, 2019
Wednesday
Hour: 00:00

High Resolution Astronomy with Infrared Interferometry

Prof. Dr. Reinhard Genzel
The Center of our Galaxy is a unique laboratory for exploring the astrophysics around a massive black hole and testing General Relativity in this extreme environment. I will discuss the results of a major campaign of observing the Galactic Center in 2017/2018 with three instruments at the European Southern Observatory's VLT, including the novel GRAVITY interferometric beam combiner of the four 8-meter telescopes. During this period the B-star S2 completed a peri-passage at ~1400 Schwarzschild radii around the compact radio source SgrA*, and permitted for the first time a test of the equivalence principle and the detection of the first post-Newtonian orbital elements in a classical 'clock experiment' around a massive black hole. During bright states (
Date:
Seminars
29
April, 2019
Monday
Hour: 14:15

Period doubling as an early warning signal for desertification

Omer Tzuk
Department of Physics of Complex Systems
The predictions for a warmer and drier climate and for increased likelihood of climate extremes raise high concerns about the possible collapse of dryland ecosystems, and about the formation of new drylands where native species are less tolerant to water stress. Using a dryland-vegetation model for plant species that display different tradeoffs between fast growth and tolerance to droughts, we find that ecosystems subjected to strong seasonal variability, typical for drylands, exhibit a period-doubling route to chaos that results in early collapse to bare soil. We further find that fast-growing plants go through period doubling sooner and span wider chaotic ranges than stress-tolerant plants. We propose the detection of period-doubling signatures in power spectra as early indicators of ecosystem collapse that outperform existing indicators in their ability to warn against climate extremes and capture the heightened vulnerability of newly-formed drylands.
Date:
Colloquia
18
April, 2019
Thursday
Hour: 11:15-12:30

The dark Universe studied from deep underground: Exploring the low-mass frontier

Federica Petricca
Today, many observations on various astronomical scales provide compelling evidence for the existence of dark matter. Its underlying nature, however, remains an open question of present-day physics. The CRESST experiment is a direct dark matter search which aims to measure interactions of potential dark matter particles in an earth-bound detector, using scintillating CaWO4 crystals as target material operated as cryogenic calorimeters at millikelvin temperatures. Each interaction in CaWO4 produces a phonon signal in the target crystal and also a light signal that is measured by a secondary cryogenic calorimeter. This technology is particularly sensitive to small energy deposits induced by light dark matter particles, allowing the experiment to probe the low-mass region of the parameter space for spin-independent dark matter-nucleon scattering with high sensitivity. Results obtained in the first run of CRESST-III with a detector achieving a nuclear recoil threshold of 30.1 eV, probing dark matter particle masses down to 0.16 GeV/c2, will be presented.
Date:
Seminars
15
April, 2019
Monday
Hour: 14:15

Growth dynamics and complexity of national economies in the

A.L. Stella
Department of Physics of Complex Systems
Methods of statistical physics allow to explore the quantitative nexus among economic growth of a country, diversity of its productions, and evolution in time of its export basket(*). A stochastic model of evolution, calibrated on data for 1238 exports from 223 countries in 21 years, enables counterfactual analyses based on estimates of the part of growth due to resource transfers between different productions. Original use of the Boltzmann-Shannon entropy function leads to the construction of consistent measures of the efficiency of national economies and of the specialization of productions. Comparisons with dynamical and GDP pc data lead to clear distinctions among developed, developing, underdeveloped and risky countries. Perspective applications of the entropic measures in other fields (ecology, microbiology,..) where diversity has to be estimated from bipartite networks will be shortly outlined. (Work in collaboration with G. Teza, University of Padova, and M. Caraglio, Katholieke Universiteit Leuven.)
Date:
Seminars
08
April, 2019
Monday
Hour: 14:15

Emergence and stability of a Brownian motor

Alex Feigel
Department of Physics of Complex Systems
A Brownian motor rectifies thermal noise and creates useful work. Here we address how this machine can emerge without predefined energy minimum in a system out of thermal equilibrium. Intuitively, Brownian motor as any artificial or biological machine should degrade with time. I will show that on contrary, a system with multiple degrees of freedom out of thermal equilibrium can be stable at a state that generates useful work. It is demonstrated with the help of ab initio analysis of a modified Feynman-Smoluchowski ratchet with two degrees of freedom. Out of thermal equilibrium, an environment imposes effective mechanical forces on nano-fabricated devices as well as on microscopic chemical or biological systems. Thus out of thermal equilibrium environment can enforce a specific steady state on the system by creating effective potentials in otherwise homogeneous configuration space. I present an ab initio path from the elastic scattering of a single gas particle by a mechanical system to the transition rate probability between the states of the system with multiple degrees of freedom, together with the corresponding Masters-Boltzmann equation and the average velocities of the system’s degrees of freedom as functions of the macroscopic parameters of the out-of-equilibrium environment. It results in Onsager relations that include the influence of the different degrees of freedom on each other. An interesting finding is that some of these forces persist even in a single temperature environment if the thermodynamic limit does not hold. In addition, the spatial asymmetry of the system’s stable state, together with the corresponding directed motion, may possess preferred chiral symmetry.
Date:
Colloquia
04
April, 2019
Thursday
Hour: 11:15-12:30

Quantum photonics for a new level of computer security and enhanced quantum computer architectures

Prof. Philip Walter
The precise quantum control of single photons, together with the intrinsic advantage of being mobile make optical quantum system ideally suited for delegated quantum information tasks, reaching from well-established quantum cryptography to quantum clouds and quantum computer networks. Here I present that the exploit of quantum photonics allows for a variety of quantum-enhanced data security for quantum and classical computers. The latter is based on feasible hybrid classical-quantum technology, which shows promising new applications of readily available quantum photonics technology for complex data processing. At the end I will also show how optical quantum computers allow for novel architectures that rely on superimposed order of quantum gates. As outlook I will discuss technological challenges for the scale up of photonic quantum computers, and our group’s current work for addressing some of those.
Date:
Seminars
31
March, 2019
Sunday
Hour: 13:00

Geometry, defects and motion in active matter

Luca Giomi
Department of Physics of Complex Systems
The paradigm of “active matter” has had notable successes over the past decade in describing self-organization in a surprisingly broad class of biological and bio-inspired systems: from flocks of starlings to robots, down to bacterial colonies, motile colloids and the cell cytoskeleton. Active systems are generic non-equilibrium assemblies of anisotropic components that are able to convert stored or ambient energy into motion. In this talk, I will discuss some recent theoretical and experimental work on active nematic liquid crystals confined on two-dimensional curved interfaces and highlight how the geometrical and topological structure of the environment can substantially affect collective motion in active materials, leading to spectacular life-like functionalities.
Date:
Colloquia
28
March, 2019
Thursday
Hour: 11:15-12:30

Towards a Periodic Table Topological Materials

Andrei bernevig
In the past few years the field of topological materials has uncovered many materials which have topological bands: bands which cannot be continuable to a trivial, “atomic” limit, and which are characterized by an integer topological index. We will review the progress in the field and the new types of topological behavior that is expected from the many predictions in the field. We will also show how, using a new theory called Topological Quantum Chemistry, thousands of new topological materials can be predicted, classified and discovered. The result is that- so far - out of 30000 materials investigated - at least 30 percent of all materials in nature can be classified as topological. One ultimately aims for a full classification of topological materials, available on database websites such as www.topologicalquantumchemistry.com
Date:
Seminars
25
March, 2019
Monday
Hour: 14:15

Hyperuniformity of driven suspensions

Haim Diamant
Department of Physics of Complex Systems
An arrangement of particles is said to be "hyperuniform" if its density fluctuations over large distances are strongly suppressed relative to a random configuration. Crystals, for example, are hyperuniform. Recently, several disordered materials have been found to be hyperuniform. Examples are sheared suspensions and emulsions, and, possibly, random close packings of particles. We show that externally driven particles in a liquid suspension (as in sedimentation, for example) self-organize hyperuniformly in certain directions relative to the external force. This dynamic hyperuniformity arises from the long-range coupling, induced by the force and carried by the fluid, between the concentration of particles and their velocity field. We obtain the general requirements, which the coupling should satisfy in order for this phenomenon to occur. Under other conditions (e.g., for certain particle shapes), the coupling can lead to the opposite effect -- enhancement of density fluctuations and instability. We confirm these analytical results in a simple two-dimensional simulation.
Date:
Seminars
18
March, 2019
Monday
Hour: 14:15

Effects of Stochasticity and non-locality on a model of aggregation-fragmentation for Saturn rings

Bijoy Daga
Department of Physics of Complex Systems
Saturn rings are composed of water-ice particles and traces of rocky materials whose sizes may vary from micro meters to a few meters. A model that describes the observed size distribution considers aggregation and fragmentation of ring particles upon collision and the distribution can be calculated analytically by solving the steady state Smoluchowski equation. In writing down the deterministic Smoluchowski equation, it is assumed that the total mass is infinite. We try to understand the behavior of the system when the total mass is finite and the effects of Stochasticity becomes important. Further, it has been observed that the steady state in these systems becomes unstable and shows oscillations for non-local reaction Kernels. We will also discuss the role of non-locality for the case of finite total mass when Stochasticity becomes relevant and see whether oscillations would survive or not.
Date:
Seminars
17
March, 2019
Sunday
Hour: 13:00

Phase separation in multicomponent liquid mixtures

Andrej Kosmrlj
Department of Physics of Complex Systems
Multicomponent systems are ubiquitous in nature and industry. While the physics of binary and ternary liquid mixtures is well-understood, the thermodynamic and kinetic properties of N-component mixtures with N>3 have remained relatively unexplored. Inspired by recent examples of intracellular phase separation, we investigate equilibrium phase behavior and morphology of N-component liquid mixtures within the Flory-Huggins theory of regular solutions. In order to determine the number of coexisting phases and their compositions, we developed a new algorithm for constructing complete phase diagrams, based on numerical convexification of the discretized free energy landscape. Together with a Cahn-Hilliard approach for kinetics, we employ this method to study mixtures with N=4 and 5 components. In this talk I will discuss both the coarsening behavior of such systems, as well as the resulting morphologies in 3D. I will also mention how the number of coexisting phases and their compositions can be extracted with Principal Component Analysis (PCA) and K-Means clustering algorithms. Finally, I will discuss how one can reverse engineer the interaction parameters and volume fractions of components in order to achieve a range of desired packing structures, such as nested "Russian dolls" and encapsulated Janus droplets.
Date:
Colloquia
14
March, 2019
Thursday
Hour: 11:15-12:30

Plasmas at the extreme

Luis O. Silva
Many astrophysical and laboratory scenarios share common underlying microphysics, and collective plasma effects associated with intense fields can have direct consequences on the plasma dynamics. These mechanisms, also involving QED effects, are highly nonlinear and multi scale, and require a combination of theory and large scale numerical simulations. The main challenges to address these scenarios will be discussed, as well as recent progresses triggered by large scale simulations of compact objects or of conditions in their vicinity, and developments on multi dimensional laser/beam plasma interactions in the presence of fields close to the critical Schwinger field, as expected in the most intense lasers now being built or in the most advanced particle accelerators. The connections between these scenarios will be discussed, emphasising the interplay between collective plasma dynamics and QED processes. Examples from both laboratory and astrophysical conditions will be provided.
Date:
Colloquia
07
March, 2019
Thursday
Hour: 11:15-12:30

The European Extremely Large Telescope

Jason Spyromilio
The European Southern Observatory is constructing a 39-m optical infrared telescope. This 1.2 Billion Euro project when completed in 2024 will be the largest telescope ever built with unprecedented collecting area and with Adaptive Optics incorporated diffraction limited operations are the baseline. The design and challenges of the project shall be described. Some aspects of the diverse science cases shall be presented as will the current technical status.
Date:
Colloquia
28
February, 2019
Thursday
Hour: 11:15-12:30

Challenges for physical cosmology after Planck

Prof. Matias Zaldarriaga
I will discuss the current status of physical cosmology after the latest Cosmic Microwave Background and other measurements. I will discuss the questions that still remain open in the field and how we might go about answering them. I will describe some recent theoretical developments that might contribute useful tools for overcoming some of the challenges that lie ahead.
Date:
Seminars
25
February, 2019
Monday
Hour: 14:15

Soft excitations in glassy systems: Universal statistics, localization and structure-dynamics relations

Eran Bouchbinder
Glassy systems exhibit various universal anomalies compared to their crystalline counterparts, manifested in their thermodynamic, transport and strongly dissipative dynamical properties. At the heart of understanding these phenomena resides the need to quantify glassy disorder and to identify excitations that are associated with it. In this talk, I will review our recent progress in addressing these basic problems. I will first establish the existence of soft nonphononic excitations in glasses, which has been debated for decades. These low-frequency glassy excitations feature a localization length in space and follow a universal gapless density of states, and they are associated with the generic existence of frustration-induced internal-stresses in glasses. I will then discuss two major implications of these localized excitations: (i) Their relation to soft spots inside glassy structures that can be identified once the spatial distribution of the heat capacity is considered. These allow us to develop predictive structure-dynamics relations in the context of irreversible (plastic) rearrangements under nonlinear driving forces. (ii) Their effect on energy transport, in particular I will show that they lead to deviations from Rayleigh scattering scaling in the attenuation of sound. Open questions will be briefly mentioned.
Date:
Colloquia
21
February, 2019
Thursday
Hour: 11:15-12:30

The physics of crushing and smashing

Prof. Shmuel Rubinstein
Understanding the physics of irreversible processes that occur in far from equilibrium systems is of both fundamental and practical importance. However, these problems pose unique challenges as dynamic irreversible processes are far from steady and probing them requires keeping up with them as the system navigates across a complex landscape. Such challenges, as they manifest in turbulence, were beautifully portrayed by Richardson: “Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity” Lewis Fry Richardson (1922)   This statement captures the essence of the turbulent cascade—the conveyance of kinetic energy across scales that underlies the universal dynamics of turbulent flows. Indeed, such conveyance of important physical quantities (energy, stress, frustration and even information) down and up a vast range of scales underlie the dynamics of many systems. For example, these same concepts hold for multi-contact frictional interfaces that form and break, for correlated defect structures that determine the strength of metals, and even in intricate networks of creases that form when a thin sheet of paper is crumpled or a soda can is smashed. We have developed experimental techniques that enable one to capture these dynamic events across multiple time and length scales. In this talk, I will describe our observations on several irreversible systems using these new tools that shed new light on their far from equilibrium behavior.
Date:
Seminars
17
February, 2019
Sunday
Hour: 13:00

Survival of the fittest, flattest, stabelest...

Yitzchak Pilpel, WIS
Department of Physics of Complex Systems
Evolution is “survival of the fittest”, but how is “fittest” defined? In simplest definitions, the fittest is the one who reproduces the fastest or with highest number of offspring. However, theories suggest that at certain situations others could be selected for. I will discuss two interesting cases. In communities that generate public goods, cooperators and defectors form more complicated evolutionary dynamics in which “fittest” depends on frequency of each strategy. Separately, the ability of evolution to select for the fastest reproducing variant is also balanced against the rate of mutations, and the quasi species theory predicts that at sufficiently high mutation rate the fastest might not necessarily be selected for. My lab employs synthetic DNA libraries and lab evolution to examine complex communities that reveal who really survives in evolution as a function of community structure and mutation rates. This very informal talk will present thoughts and challenges and preliminary results along these lines.
Date:
Seminars
11
February, 2019
Monday
Hour: 14:15

Symbolic dynamics for maps on surfaces

Omri Sarig,
Department of Physics of Complex Systems
: I will review some of the ideas used by mathematicians to study the ergodic theory of "chaotic" smooth invertible maps on surfaces. Symbolic dynamics allows to "change coordinates" and pass to a model similar to the configuration space of a 1D lattice gas model. Analogies to equilibrium statistical physics can then be employed to study the dynamic and stochastic properties of the system.
Date:
Colloquia
07
February, 2019
Thursday
Hour: 11:15-12:30

The Biomass Distribution on Earth

Prof. Ron Milo
A census of the biomass on Earth is key for understanding the structure and dynamics of the biosphere. Yet, a quantitative, global view of how the biomass of different taxa compare with each other is still lacking. In this study, we harness recent advances in global sampling techniques to assemble the overall biomass composition of the biosphere, establishing the first census of the biomass of all the kingdoms of life.
Date:
Seminars
04
February, 2019
Monday
Hour: 14:15

Towards a new understanding of disorder and dissipation in solids

Alessio Zaccone
Department of Physics of Complex Systems
Solid-state theory has been formulated in the 20th century on the assumptions of regular crystalline lattices where linear dynamics holds at both classical and quantum levels, while dissipative effects are taken into account to perturbative order. While considerable success has been achieved in the further understanding of disorder effects on the electronic properties of solids, the same is not true for the thermal, vibrational and mechanical properties due to the difficulty of reformulating the whole body of lattice dynamics in a non-perturbative way for disordered systems. I will present a formulation of lattice dynamics extended (in a non-perturbative way) to disordered systems, called Nonaffine Lattice Dynamics (NALD), successfully tested on different systems [1-3]. I will then consider the effect of viscous dissipation on the lattice dynamics of crystalline solids and show how dissipation can lead, in perfectly ordered crystals, to effects very similar to disorder-induced effects in glasses. Theory can explain all these surprising effects in perfect crystals as a result of anharmonic damping inducing diffusive modes that compete with propagating modes [4], and also predicts similar effects resulting from low-lying soft optical phonons (experimentally confirmed). This framework may lead to a new quantitative connection between lattice/atomic parameters, electron-phonon coupling and the Tc of superconductors with the possibility, in future work, of rationalizing a variety of experimental data and to provide a more quantitative (less empirical) understanding of how Tc can be varied in conventional and perhaps also more exotic superconductors. [1] A. Zaccone and E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). [2] R. Milkus and A. Zaccone, Phys. Rev. B 93, 094204 (2016). [3] V.V. Palyulin, C. Ness, R. Milkus, R.M. Elder, T.W. Sirk, A. Zaccone, Soft Matter 14, 8475 (2018). [4] M. Baggioli and A. Zaccone, arXiv:1810.09516v1 [cond-mat.soft].
Date:
Seminars
04
February, 2019
Monday
Hour: 14:15

Towards a new understanding of disorder and dissipation in solids

Alessio Zaccone
Department of Physics of Complex Systems
Solid-state theory has been formulated in the 20th century on the assumptions of regular crystalline lattices where linear dynamics holds at both classical and quantum levels, while dissipative effects are taken into account to perturbative order. While considerable success has been achieved in the further understanding of disorder effects on the electronic properties of solids, the same is not true for the thermal, vibrational and mechanical properties due to the difficulty of reformulating the whole body of lattice dynamics in a non-perturbative way for disordered systems. I will present a formulation of lattice dynamics extended (in a non-perturbative way) to disordered systems, called Nonaffine Lattice Dynamics (NALD), successfully tested on different systems [1-3]. I will then consider the effect of viscous dissipation on the lattice dynamics of crystalline solids and show how dissipation can lead, in perfectly ordered crystals, to effects very similar to disorder-induced effects in glasses. Theory can explain all these surprising effects in perfect crystals as a result of anharmonic damping inducing diffusive modes that compete with propagating modes [4], and also predicts similar effects resulting from low-lying soft optical phonons (experimentally confirmed). This framework may lead to a new quantitative connection between lattice/atomic parameters, electron-phonon coupling and the Tc of superconductors with the possibility, in future work, of rationalizing a variety of experimental data and to provide a more quantitative (less empirical) understanding of how Tc can be varied in conventional and perhaps also more exotic superconductors. [1] A. Zaccone and E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). [2] R. Milkus and A. Zaccone, Phys. Rev. B 93, 094204 (2016). [3] V.V. Palyulin, C. Ness, R. Milkus, R.M. Elder, T.W. Sirk, A. Zaccone, Soft Matter 14, 8475 (2018). [4] M. Baggioli and A. Zaccone, arXiv:1810.09516v1 [cond-mat.soft].