Groups | Seminars || Courses | Outreach

Seminars

Seminars will be held held at room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise.

Fall 2014

September 8, 2014 Prof. Arno Rauschenbeutel Vienna University of Technology,  Austria Coupling, controlling, and processing non-transversal photons with a single atom (Host: Hal Metcalf)

I will report on recent experimental investigations of the interaction between single rubidium atoms and light that is confined by continuous total internal reflection in a whispering-gallery-mode (WGM) bottle microresonator. These resonators offer the advantage of very long photon lifetimes in conjunction with near lossless in- and out-coupling of light via tapered fiber couplers. We discovered that the non-transversal polarization of WGMs fundamentally alters the physics of light-matter interaction [1]. Taking advantage of this effect, we recently demonstrated switching of signals between two distinct optical fibers controlled by a single atom [2]. Owing to the excellent optical properties of our bottle microresonator, the scheme yields high switching fidelities and low losses. Furthermore, we exploited the strong birefringence of the bottle microresonator and implemented a single-atom-controlled polarization flip of the light that is guided through the coupling fiber [3]. And finally, we made use of the strong nonlinear response of the atom-resonator system and experimentally realized an optical Kerr nonlinearity at the level of single photons [3]. Analyzing the transmitted light, we observe a nonlinear phase shift of ? between the cases of one and of two photons passing the resonator. This phase shift leads to entanglement between previously independent fiber-guided photons, which we verify by performing a full quantum state tomography of the transmitted two-photon state. [1] C. Junge et al., Phys. Rev. Lett. 110, 213604 (2013). [2] D. O'Shea et al., Phys. Rev. Lett. 111, 193601 (2013). [3] J. Volz et al., arXiv:1403.1860 (2014).

September 15, 2014 Prof. Pierre Meystre University of Arizona Quantum Optomechanics and Quantum Heat Engines (Host: Hal Metcalf)

Quantum optomechanics offers considerable promise both in fundamental and in applied science, with the potential of gaining a deeper understanding of the quantum-classical transition, and also of developing sensors capable of probing extremely feeble forces, often with spatial resolution at atomic scales. Its rapid development is the result of a convergence from two perspectives on the physical world. From the top down, ultra-sensitive micromechanical and nanomechanical detectors have become available utilizing the advanced materials and processing techniques of the semiconductor industry and nanoscience. And from the bottom-up perspective, quantum optics and atomic physics have yielded an exquisite understanding of the mechanical aspects of light–matter interaction, including how quantum mechanics limits the ultimate sensitivity of measurements and how measurement backaction can be harnessed to control quantum states of mechanical systems. After a tutorial general introduction, the talk will discuss selected recent advances, concentrating on the development of quantum heat engines that may help address fundamental questions in quantum thermodynamics.

September 22, 2014 Prof. Chris Johnson SBU Chemistry Dynamics and Spectroscopy of Small Molecules and Molecular Ions (Host: Tom Allison)

Despite their size, molecules smaller than ten atoms still hold mysteries of interest in chemistry and chemical physics.  This talk will cover two topics in which new insights have been gained through significant experimental advances in the preparation and storage of ions at cryogenic temperatures.  First, I will explore the role of tunneling in the reaction OH + CO -> H + CO_2, a benchmark system for quantum dynamics calculations.  Experiments directly probing H-atom tunneling lifetimes on the order of microseconds have provided critical data in the poorly characterized exit channel region of the potential energy surface governing this reaction.  I will also discuss recent results on the rovibrational spectroscopy of the NH_4+H_2O(He)_ system in which the binding of n = 3 helium atoms to NH groups shows no significant effect on the rotational constant of the NH_3 rotor.  These results are interpreted in the context of weak coupling of independent rotors.

September 29, 2014 Dr. Swati Singh ITAMP/Harvard University Coupling single quantum systems to spin baths (Host: Hal Metcalf)

The study of the interaction between quantum systems and their environment is central to the understanding of a broad range of problems. Important examples include the elusive quantum to classical transition, as illustrated most famously by the Schroedinger cat paradox, and non-equilibrium dynamics, as illustrated by the central spin problem. On the applied side, this understanding is an essential step towards quantum metrology, including the development of quantum noise limited detectors. Environments composed of quantum spins are particularly intriguing due to their nonlinear interactions with the system, a result of their inherent quantum nature. Following a general introduction I will illustrate key features of such environments in two simple and experimentally realizable examples: a nitrogen vacancy (NV) center in diamond interacting with its nuclear spin environment, and a single motional mode of a macroscopic mechanical oscillator interacting with a cloud of spin-1 cold atoms. In the first case I will demonstrate within a semiclassical description that it is possible to monitor and cool the nuclear spin bath by optically pumping the electronic spin of the NV center. In the second example I will show that by coupling an oscillator to a cloud of cold atoms and manipulating the spin of the atomic ensemble it is possible to cool and manipulate the motional states of a harmonic oscillator.

October 9, 2014 (Thurs, 4:00pm) Prof. Cord Müller Universität Konstanz, Germany Localization loop spectroscopy for cold atoms in random potentials (Host: Dominik Schneble)

In phase-coherent systems, strong scattering by quenched disordered can suppress the classical real-space diffusion of matter waves, a phenomenon known as Anderson localization. While difficult to realize with strongly interacting electrons, Anderson localization and its precursor, weak localization or coherent back-scattering, are today much studied with ultracold atoms in laser speckle potentials. In this talk, I will first present our ideas of how to probe subtle processes of quantum interference by "loop echo spectroscopy” and thus to arrive at a more refined understanding of the onset of Anderson localization. Secondly, I will discuss a specific signature for fully developed Anderson localization that is predicted to be available in momentum space, namely a characteristic  forward-scattering coherence peak that complements the familiar back-scattering peak. References: T. Micklitz, C.A. Müller, A. Altland, arXiv:1406.6915 and PRL 112, 110602 (2014)

October 13, 2014 Prof. David Reis SLAC/Stanford University Hard x-ray nonlinear optics (Host: Tom Allison)

X-ray free electron lasers can produce focused beams with peak electric field easily exceeding the atomic unit and only four orders of magnitude below the QED critical field.  Advances in FEL technology and x-ray focusing could yield substantially higher fields.  Under such conditions x-ray matter interactions becomes nonlinear, although the dominant nonlinearities to date tend to be related to sequential processes.  Here we present the observation of coherent nonsequential processes at hard x-ray energies including:  phase-matched second harmonic generation in diamond and two-photon Compton scattering in beryllium.  The former can be described in terms of a free-electron like nonlinearity, however, we find that this approximation breaks down spectacularly in the latter.

November 5, 2014 (joint AMO-Astro seminar,  Wed, 2:30pm in ESS450) Prof. Robert Forrey Penn State Berks From molecules to the first stars (Host: Tom Bergeman)

Cooling through excitation of molecular hydrogen catalyzed the formation of the first stars in the universe, the so-called Population III stars. At low densities, H2 molecules were produced primarily by a reaction sequence initiated by H-.  As the gravitational collapse proceeded, the density increased to the point where three-body recombination became the dominant mechanism for molecule production. This talk will describe recent efforts to improve the accuracy of molecular hydrogen formation rates, which are crucial for reliable modeling of the formation of the first stars.

November 10, 2014 Dr. Ali Belkacem LBNL Photon and electron driven non-Born-Oppenheimer dynamics in polyatomic molecules (Host: Tom Weinacht)

AMO studies have shaped our understanding of electron correlation, single photon multiple ionization, Auger processes, and photo-dissociation dynamics, all processes that are fundamentally important and occur in more complex chemical and biological systems. The commonality of the broad spectrum of the portfolio of photon and electron scattering studies is the use of targets that are in their ground state.  In the case of photon-driven chemistry, the unprecedented ability of having two or three tailored extreme-ultraviolet photons opens up a large spectrum of possibilities that will help shed light on some of the most basic electronic and molecular processes that take place in excited states and drive photochemistry.  Electronic processes such as auto-ionization or radiative decay tend to quench these neutral and ionic excited states on very short timescale. Consequently, nuclear dynamics, isomerization and redistribution of energy between the various nuclear degrees of freedom, have to be very fast to compete with these relaxation mechanisms. Nuclear and electronic degrees of freedom tend to couple and interesting non-adiabatic phenomena are known to arise. A particularly important example is conical intersections.  Because of the breakdown of the Born-Oppenheimer approximation, conical intersections provide pathways for ultrafast interstate crossing, typically on the femtosecond time scale.  Conical intersections can be found already in low-lying states of very simple molecules such as water, ethylene, carbon dioxide, or somewhat more complex systems such as formic acid or uracil. My talk will focus on the progress made using ultrafast lasers as well as low-energy electron sources coupled with momentum imaging.

December 4, 2014 (joint YITP-AMO seminar, Wed, 1PM in  the YITP common room) Dr. Kuei Sun U. Texas at Dallas Spin-related superfluid phases in ultra-cold quantum gases (Host: Tzu-Chieh Wei)

I would like to present our recent study on novel superfluid phenomena in Bose-Einstein condensates (BEC) and degenerate Fermi gases (DFG) by engineering the spin degrees of freedom of ultra-cold atoms. In the bosonic case, we propose to realize spin and orbital angular momentum coupling in a BEC and study its ground state properties in a ring geometry. Such system is naturally subject to the angular momentum quantization and exhibits strong many-body physics in contrast with common spin-linear momentum coupled superfluids in experiments. In the fermionic case, we study spatially oscillatory pairing (FuldeFerrellLarkinOvchinnikov or FFLO order) in DFG superfluid with th spin imbalance, with focus on an experimental system in tubular optical lattices. We find the evolution of the FFLO order as the lattice depth varies and an interesting phase diagram for the unpaired majority spins. Our results could help the search for the elusive FFLO order, proposed about half century ago. Refs: arXiv:1411.1737; PRA 87, 053622 (2013); PRA 85, 051607(R) (2012).

December 8, 2014 Dr. Rita Kalra Harvard University Antimatter trapping at CERN for tests of fundamental symmetries (Host: Hal Metcalf)

The recent demonstration of trapped antihydrogen–the simplestt antimatter atom–is a milestone towards precise spectroscopy for teests of CPT invariance. In this talk, I will introduce the ATRAP experiment, which utilizes antiproton and positron plasmas in a combined Penning-Ioffe trap to create and magnetically confine the neutral antiatoms. The synthesis and confinement of antihydrogen takes place at the antiproton decelerator at CERN, the world's only source of low-energy antiprotons. The cryogenic antihydrogen trap and the multifaceted infrastructure working in concert with the trap will be described, along with analysis methods used to discern the atoms from a cosmic ray background. The next milestone in this work is the first laser-cooling of antihydrogen. To this end, a next-generation apparatus that will allow for the confinement and improved detection of larger numbers of antihydrogen atoms has just been constructed for use in this year's antiproton beam run.

December 15, 2014 Prof. Lou DiMauro Ohio State University Attosecond Physics in the Long Wavelength Limit (Host: Tom Weinacht)

Over the last fifteen years, the tailoring of a light field for manipulating the dynamics of a system at the quantum level has taken a prevalent role in modern atomic, molecular and optical physics. As first described by Keldysh, the ionization of an atom by an intense laser field will evolve depending upon the light characteristics and atomic binding energy. Numerous experiments have thoroughly investigated the dependence of the intensity and pulse duration on the ionization dynamics of inert gas atoms. However, exploration of the wavelength dependence has been mainly limited to wavelengths less than 1Â mm, or in the language of Keldysh to the multiphoton or mixed ionization regime. It is now technically possible to perform more thorough test, and exploit, the scaling laws at wavelengths greater than 1Â mm. In addition, excitation with mid-infrared light augments a variety of atomic systems which will tunnel ionize, as well as posing different model atomic structure, e.g. one- and two-electron like systems. This talk will discuss the implication of the strong-field scaling as it pertains to the production of high energy photons and the generation of attosecond pulses. Exploiting the long wavelength limit also provides a means of performing ultra-fast imaging in a manner consistent with electron diffraction.

last updated 06/08/2014