Integrated Calendar

Realization of a quantum interface between stationary and flying qubits is a requirement for long-distance quantum communication and distributed quantum computation. The prospects for integrating many qubits on a single chip render solid-state spins promising candidates for stationary qubits. An important class of solid-state spin systems,including quantum dots and nitrogen-vacancy centers in diamond, exhibit spin-state-dependent optical transitions, allowing for fast initialization, manipulation and measurement of the spins using laser excitation. In this talk, I will describe recent experiments based on semiconductor quantum dots demonstrating spin-photon entanglement and teleportation of quantum information from a propagating photonic qubit to a confined spin qubit. These experiments pave the way for realization of entanglement between distant spin qubits.

In this talk, I will first describe our efforts to understand transformations across visual cortical areas and layers using chronic calcium imaging of cell bodies and axons in awake, behaving mice. I will then describe our preliminary efforts at linking hunger-dependent modulation of visual processing in amygdala and cortex with hypothalamic drivers of food seeking.

The production of spin-polarized hydrogen atoms produced in molecular photodissociation was considered theoretically more than thirty years ago [1], however it has been experimentally observed only recently, first by inferring based on the measured co-fragment angular momentum polarization [2], and subsequently by detection of the polarized fluorescence in the H atoms excited by Lyman-alpha radiation [3]. We present a new experimental technique allowing for direct measurement of the velocity dependence of hydrogen atom spin polarization with high resolution and sensitivity. The strategy is an adaptation of the H atom Rydberg time-of-flight approach (SP-HRTOF), where the spin-sensitive probe scheme combines a linearly polarized Lyman-α laser, a circularly polarized tagging laser, and a photolysis laser [4]. The approach is illustrated with a measurement of the H atom spin polarization in photodissociation of HBr and DBr at 212.8 nm. The two coherent contributions to the spin polarization are measured for H atoms produced in conjunction with dissociation to Br(2P3/2) and Br*(2P1/2); they are found to be negligible for the former channel but substantial for the latter, in agreement with previous theoretical predictions. The ratio of the two measurements directly gives the asymptotic scattering phase shift for dissociation along the two potentials for the H + Br* channel. The paper also discusses the means to adapt this method to detect the incoherent contribution to the photofragment spin polarization, and discuss our progress in applying the technique to dissociation of polyatomic molecules.
The presented results show the capability for SP-HRTOF to yield fundamental insights into molecular scattering processes. Applications to dissociation of polyatomic molecules and reactive and inelastic scattering promise a wealth of new detail concerning these elementary processes.

1. O.S. Vasyutinskii, Sov. Phys. JETP 1981, 54, 855-861.
2. T. P. Rakitzis, P.C. Samartzis, R.L. Toomes, T.N. Kitsopoulos, A. Brown, G.G. Balint-Kurti, O.S. Vasyutinskii, and
J.A. Beswick, Science 2003, 300, 1936.
3. D. Sofikitis, L. Rubio-Lago, L. Bougas, A.J. Alexander, and T.P. Rakitzis, The Journal of Chemical Physics 2008,
129, 144302.
4. B.M. Broderick, Y. Lee, M.B. Doyle, O.S. Vasyutinskii, and A.G. Suits, The Journal of Physical Chemistry Letters
2013, 4, 3489.
5. B. M. Broderick, Y. Lee, M. B. Doyle, V. Y. Chernyak, O. S. Vasyutinskii, A. G. Suits, Review of Scientific
Instruments, 2014, 85, 053103.

The spring phytoplankton bloom is a major, extensively studied phenomenon in temperate and high latitude seas. Much less information isavailable on blooms in subtropical oligotrophic seas, where the water column is usually stratified. Yet, even in temperate seas the processes determining phytoplankton dynamics during the mixed-layer deepening and the factors triggering the initiation of the bloom are controversial. Here we use long-term measurements of chlorophyll concentration, nutrients, mixed-layer depth and grazing rates to examine the validity of three bloom-initiation processes for the Gulf of Aqaba (northern Red Sea): the Critical Depth Hypothesis, the Dilution-Recoupling Hypothesis, and the Critical Turbulence Hypothesis. The Gulf is a unique water body in the subtropics, where convective mixing during winter reaches hundreds of meters in depth, leading to conspicuous spring blooms. Here we show that neither the critical depth mechanism nor the dilution-recoupling hypothesis explain the phytoplankton dynamics during the winter and spring in the Gulf. Instead, our findings indicate that this dynamics is governed by the interplay between three main processes: (1) nutrient-driven primary production in the upper, illuminated layer; (2) physical ‘homogenization’ of phytoplankton by convective mixing; and (3) accumulation of phytoplankton in the upper layer after the termination of sea-surface cooling. The latter mechanism is responsible for the onset and magnitude of the spring bloom.