Past Events

Abstract: The second quantum revolution relies on our ability to control and measure individual quantum states in micro- and nanoscopic systems, such as atoms, ions, and quantum dots. The techniques resulting from this capability may lead to a considerable improvement in several sensing modalities, for example atomic clocks and the measurement of magnetic fields on the nanoscale. As an example for a quantum sensor, and of course after introducing the underlying concepts of quantum sensing, I will present the nitrogen-vacancy defect, or color center, in diamond. First, I will explain how one can use it to measure magnetic and electric fields, temperature, strain and even pH levels. Then, I will try to show what the "quantum advantage" that is possible in this class of sensors and will give a few examples from research activities in our group. Finally, I will also discuss several industrial applications, some of which are already in use or in development around the world.

Abstract: I will describe the photonic approach to quantum computation, which is the only technology that has been originally designed to reach the massive scaling required for fault- tolerant universal computation (> 106 physical qubits). It combines topological error correction and measurement-based quantum computation, with the leading effort relying on massive-scale silicon photonics. I will then describe how cavity-QED with single atoms allows deterministic photon-atom two qubit gates, which in turn can drastically simplify the road towards fault-tolerant photonic quantum computing and improve its scaling to even larger numbers of physical qubits.

Abstract: It is fairly well known that Shor's algorithm for Factoring and Discrete Logarithm poses a challenge for cryptography in a quantum world. However, the implications of the viability of the quantum model on cryptography are much more profound, on a number of aspects. Naturally, it is harder to protect against quantum attackers than against classical ones, especially if the honest users remain classical. On the other hand, quantum computation and communication also present new tools that may assist in performing some cryptographic tasks. Further, the quantum model brings about new potential capabilities and cryptographic tasks that need to be explored, most basically the ability to prove that a potentially untrusted device indeed performs a quantum task. In the talk I will explain how computer scientists, and in particular cryptographers, perceive the quantum computing model. I will discuss some of the fundamental questions that come up when the quantum model is incorporated into cryptography, such as the security of "lattice assumptions" against quantum attacks, the rewinding problem in cryptographic reductions, and the notion of semi-quantum cryptography which addresses questions in classical-quantum interaction. No background in computer science or cryptography will be assumed. Hybrid seminar Location: Physics library (Benoziyo Physics building, second floor) Zoom link: https://weizmann.zoom.us/j/99771276053?pwd=K3N6NEpPemh6aDZ2dEpJUU5HRXo4UT09

Abstract: In this talk I will review the basic methods and the current state-of-the-art in trapped ion quantum computing and compare the advantages and disadvantages of this to other QC technologies. I will further describe the progress towards building the WeizQC - a trapped ion quantum computer at the Weizmann Institute of Science. In the second part of the talk I will describe one unique feature of trapped-ion qubits: their all-to-all connectivity. I will describe methods that use this connectivity to engineer multi-qubit gates and operations. Multi-qubit gates have many advantages, both for near term noisy quantum computers, as well as for achieving fault-tolerance. As an example I will show that using multi-qubit gates, the threshold for fault-tolerant quantum computing can be enlarged and the ratio of logical to physical qubit error reduced.

Abstract: Many problems of interest, ranging from condensed matter physics and quantum chemistry to quantum information, require finding the ground state of a system of many interacting degrees of freedom (e.g., qubits or quantum spins). The main challenge stems from the exponential scaling of the Hilbert space dimension with the number of qubits. I will first discuss various strategies to tackle this problem using classical computers, such as tensor network states and Monte Carlo sampling, and their limitations. Quantum computers are ideally suited for this task; I will present a proposal to simulate quantum systems on noisy intermediate-scale quantum (NISQ) devices made of imperfect qubits, where the noise level translates into a finite energy density (i.e., finite temperature).

Abstract: Topological Insulators (TIs) are a newly discovered class of materials in which symmetry-protected conducting modes exist on the surface of a bulk insulator. They hold promise for realizing a variety of fundamentally interesting and technologically relevant electronic phases, ranging from quantized magnetoelectric effects to device structures that support extremely high thermoelectric performance. Surprisingly, removing symmetries from these materials – including those that underlie their fundamental protection – has proven to be on the most incisive ways of examining TIs and reaching towards these exotic electronic behaviors. I will discuss our materials oriented approach to breaking symmetry in TIs and the new behavior is has uncovered with a focus on emergent quantum Hall phases.

Abstract: I will give examples from various fields to show the ubiquity of oxides for a number of applications. Compared to dominantly covalent semiconductors like silicon and the III-V or II-VI materials oxides are primarily ionic bonded and also have extensive oxygen bonding and the oxygen bonds play a crucial role in determining the property of the material and give oxides a level of diversity not seen in covalent semiconductors. It is frequently argued by the semiconductor community that oxides are prone to defects and hence are inherently unstable for technologies. However, defects in oxides play a crucial role in controlling the material properties and I will illustrate this with the example of ferromagnetism in TiO2 via titanium vacancies. This is achieved by substituting Ta in the place of Ti which leads to a significant donor electron population stimulating the formation of compensating defects such as Ti vacancies and Ti3+. As a function of film thickness one sees ferromagnetism, Kondo scattering and eventually impurity scattering in the same system revealing the diversity of interactions. For the technologies beyond Moore silicon photonics is evolving at a rapid phase with a corresponding Moore’s law projection extending up to 2025. The area of opportunity is the growth of functional oxides on silicon to build switchable devices which will significantly enhance the capability of the future silicon packages integrating multiple chips. In today’s computing devices more than 25% of the energy is consumed in memories and a typical server station expends 55% of its energy on memories. Ferroelectric tunnel junctions may play a crucial role in the development of low energy consuming memory devices. I will show results on oxide based ferroelectric tunnel junctions where just two unit cells of barium titanate enable a robust switching of a junction with On/Off ratios exceeding 1000%. Oxides, because of their chemical stability may be important for applications such as water splitting, CO2 sequestration etc. I will illustrate this with the example of a new class of materials, Sr, Ca and Ba Niobates which show a very unusual band structure when prepared under different oxygen pressures. Lastly but not the least I will illustrate the potential for oxides in controlling bio processes such as bio film formation cell proliferation and differentiation where the surface chemistry seems to play a crucial role in controlling the processes.

Abstract: I will give examples from various fields to show the ubiquity of oxides for a number of applications. Compared to dominantly covalent semiconductors like silicon and the III-V or II-VI materials oxides are primarily ionic bonded and also have extensive oxygen bonding and the oxygen bonds play a crucial role in determining the property of the material and give oxides a level of diversity not seen in covalent semiconductors. It is frequently argued by the semiconductor community that oxides are prone to defects and hence are inherently unstable for technologies. However, defects in oxides play a crucial role in controlling the material properties and I will illustrate this with the example of ferromagnetism in TiO2 via titanium vacancies. This is achieved by substituting Ta in the place of Ti which leads to a significant donor electron population stimulating the formation of compensating defects such as Ti vacancies and Ti3+. As a function of film thickness one sees ferromagnetism, Kondo scattering and eventually impurity scattering in the same system revealing the diversity of interactions. For the technologies beyond Moore silicon photonics is evolving at a rapid phase with a corresponding Moore’s law projection extending up to 2025. The area of opportunity is the growth of functional oxides on silicon to build switchable devices which will significantly enhance the capability of the future silicon packages integrating multiple chips. In today’s computing devices more than 25% of the energy is consumed in memories and a typical server station expends 55% of its energy on memories. Ferroelectric tunnel junctions may play a crucial role in the development of low energy consuming memory devices. I will show results on oxide based ferroelectric tunnel junctions where just two unit cells of barium titanate enable a robust switching of a junction with On/Off ratios exceeding 1000%. Oxides, because of their chemical stability may be important for applications such as water splitting, CO2 sequestration etc. I will illustrate this with the example of a new class of materials, Sr, Ca and Ba Niobates which show a very unusual band structure when prepared under different oxygen pressures. Lastly but not the least I will illustrate the potential for oxides in controlling bio processes such as bio film formation cell proliferation and differentiation where the surface chemistry seems to play a crucial role in controlling the processes.

Abstract: I will give examples from various fields to show the ubiquity of oxides for a number of applications. Compared to dominantly covalent semiconductors like silicon and the III-V or II-VI materials oxides are primarily ionic bonded and also have extensive oxygen bonding and the oxygen bonds play a crucial role in determining the property of the material and give oxides a level of diversity not seen in covalent semiconductors. It is frequently argued by the semiconductor community that oxides are prone to defects and hence are inherently unstable for technologies. However, defects in oxides play a crucial role in controlling the material properties and I will illustrate this with the example of ferromagnetism in TiO2 via titanium vacancies. This is achieved by substituting Ta in the place of Ti which leads to a significant donor electron population stimulating the formation of compensating defects such as Ti vacancies and Ti3+. As a function of film thickness one sees ferromagnetism, Kondo scattering and eventually impurity scattering in the same system revealing the diversity of interactions. For the technologies beyond Moore silicon photonics is evolving at a rapid phase with a corresponding Moore’s law projection extending up to 2025. The area of opportunity is the growth of functional oxides on silicon to build switchable devices which will significantly enhance the capability of the future silicon packages integrating multiple chips. In today’s computing devices more than 25% of the energy is consumed in memories and a typical server station expends 55% of its energy on memories. Ferroelectric tunnel junctions may play a crucial role in the development of low energy consuming memory devices. I will show results on oxide based ferroelectric tunnel junctions where just two unit cells of barium titanate enable a robust switching of a junction with On/Off ratios exceeding 1000%. Oxides, because of their chemical stability may be important for applications such as water splitting, CO2 sequestration etc. I will illustrate this with the example of a new class of materials, Sr, Ca and Ba Niobates which show a very unusual band structure when prepared under different oxygen pressures. Lastly but not the least I will illustrate the potential for oxides in controlling bio processes such as bio film formation cell proliferation and differentiation where the surface chemistry seems to play a crucial role in controlling the processes.

Abstract: I will give examples from various fields to show the ubiquity of oxides for a number of applications. Compared to dominantly covalent semiconductors like silicon and the III-V or II-VI materials oxides are primarily ionic bonded and also have extensive oxygen bonding and the oxygen bonds play a crucial role in determining the property of the material and give oxides a level of diversity not seen in covalent semiconductors. It is frequently argued by the semiconductor community that oxides are prone to defects and hence are inherently unstable for technologies. However, defects in oxides play a crucial role in controlling the material properties and I will illustrate this with the example of ferromagnetism in TiO2 via titanium vacancies. This is achieved by substituting Ta in the place of Ti which leads to a significant donor electron population stimulating the formation of compensating defects such as Ti vacancies and Ti3+. As a function of film thickness one sees ferromagnetism, Kondo scattering and eventually impurity scattering in the same system revealing the diversity of interactions. For the technologies beyond Moore silicon photonics is evolving at a rapid phase with a corresponding Moore’s law projection extending up to 2025. The area of opportunity is the growth of functional oxides on silicon to build switchable devices which will significantly enhance the capability of the future silicon packages integrating multiple chips. In today’s computing devices more than 25% of the energy is consumed in memories and a typical server station expends 55% of its energy on memories. Ferroelectric tunnel junctions may play a crucial role in the development of low energy consuming memory devices. I will show results on oxide based ferroelectric tunnel junctions where just two unit cells of barium titanate enable a robust switching of a junction with On/Off ratios exceeding 1000%. Oxides, because of their chemical stability may be important for applications such as water splitting, CO2 sequestration etc. I will illustrate this with the example of a new class of materials, Sr, Ca and Ba Niobates which show a very unusual band structure when prepared under different oxygen pressures. Lastly but not the least I will illustrate the potential for oxides in controlling bio processes such as bio film formation cell proliferation and differentiation where the surface chemistry seems to play a crucial role in controlling the processes.

Abstract: I will give examples from various fields to show the ubiquity of oxides for a number of applications. Compared to dominantly covalent semiconductors like silicon and the III-V or II-VI materials oxides are primarily ionic bonded and also have extensive oxygen bonding and the oxygen bonds play a crucial role in determining the property of the material and give oxides a level of diversity not seen in covalent semiconductors. It is frequently argued by the semiconductor community that oxides are prone to defects and hence are inherently unstable for technologies. However, defects in oxides play a crucial role in controlling the material properties and I will illustrate this with the example of ferromagnetism in TiO2 via titanium vacancies. This is achieved by substituting Ta in the place of Ti which leads to a significant donor electron population stimulating the formation of compensating defects such as Ti vacancies and Ti3+. As a function of film thickness one sees ferromagnetism, Kondo scattering and eventually impurity scattering in the same system revealing the diversity of interactions. For the technologies beyond Moore silicon photonics is evolving at a rapid phase with a corresponding Moore’s law projection extending up to 2025. The area of opportunity is the growth of functional oxides on silicon to build switchable devices which will significantly enhance the capability of the future silicon packages integrating multiple chips. In today’s computing devices more than 25% of the energy is consumed in memories and a typical server station expends 55% of its energy on memories. Ferroelectric tunnel junctions may play a crucial role in the development of low energy consuming memory devices. I will show results on oxide based ferroelectric tunnel junctions where just two unit cells of barium titanate enable a robust switching of a junction with On/Off ratios exceeding 1000%. Oxides, because of their chemical stability may be important for applications such as water splitting, CO2 sequestration etc. I will illustrate this with the example of a new class of materials, Sr, Ca and Ba Niobates which show a very unusual band structure when prepared under different oxygen pressures. Lastly but not the least I will illustrate the potential for oxides in controlling bio processes such as bio film formation cell proliferation and differentiation where the surface chemistry seems to play a crucial role in controlling the processes.

Abstract: The LAO/STO interface hosts a two-dimensional electron system that is unusually sensitive to the application of an in-plane magnetic field. Low-temperature experiments have revealed a giant negative magnetoresistance (dropping by 70\%), attributed to a magnetic-field induced transition between interacting phases of conduction electrons with Kondo-screened magnetic impurities. Here we report on experiments over a broad temperature range, showing the persistence of the magnetoresistance up to the 20~K range --- indicative of a single-particle mechanism. Motivated by a striking correspondence between the temperature and carrier density dependence of our magnetoresistance measurements we propose an alternative explanation. Working in the framework of semiclassical Boltzmann transport theory we demonstrate that the combination of spin-orbit coupling and scattering from finite-range impurities can explain the observed magnitude of the negative magnetoresistance, as well as the temperature and electron density dependence. I will present both experimental results and our theoretical transport model.

Abstract: We investigate several questions that concern with disorder using three main methods: A. A controlled expansion in the heat capacity critical exponent. B. Large N models. C. AdS/CFT In the talk I will probably not get to say much about method C., but I will explain methods A. and B. Method A. can be used to derive concrete results about the disordered 3d Ising model. Method B. can be used to derive a certain generalization of the Imry-Ma result and also it leads to some predictions that can be cross-checked using method C. Using method B. one can also obtain closed form RG flows between pure and disordered fixed points.