Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session G6: Synthetic Gauge Fields and Spin-orbit Coupling in Cold Atoms |
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Chair: Ian Spielman, NIST Room: Delaware AB |
Wednesday, June 10, 2015 8:00AM - 8:12AM |
G6.00001: Striped ferronematic ground states in a spin-orbit coupled $S=1$ Bose gas William Cole, Stefan Natu, Xiaopeng Li We theoretically establish the mean-field phase diagram of a homogeneous spin-1, spin-orbit coupled Bose gas as a function of the spin-dependent interaction parameter, the Raman coupling strength and the quadratic Zeeman shift. We find that the interplay between spin-orbit coupling and spin-dependent interactions leads to the occurrence of ferromagnetic or ferronematic phases which also break translational symmetry. For weak Raman coupling, increasing attractive spin-dependent interactions induces a transition from a uniform to a stripe XY ferromagnet with no nematic order. For repulsive spin-dependent interactions, however, we find a transition from an XY spin spiral phase with uniaxial nematic order, to a biaxial ferronematic, where the total density, spin vector and nematic director oscillate in real space. We investigate the stability of these phases against the quadratic Zeeman effect, which generally tends to favor uniform phases with either ferromagnetic or nematic order but not both. We discuss the relevance of our results to ongoing experiments on spin-orbit coupled, spinor Bose gases. [Preview Abstract] |
Wednesday, June 10, 2015 8:12AM - 8:24AM |
G6.00002: Bragg spectroscopy of spin-orbit coupled BEC M.A. Khamehchi, Maren Mossman, Peter Engels Spin-orbit coupling plays an important role in many physical systems. In Bose-Einstein condensates, spin-orbit coupling can be induced using Raman coupling schemes. We report on our experiments utilizing Bragg spectroscopy to probe the excitation spectrum of a spin-orbit coupled BEC. The measurements reveal a roton-like minimum in the spectrum that can be modified by changing the Raman laser parameters. We will discuss the current status of the experiment and our progress toward understanding the implications of this dispersion spectrum. [Preview Abstract] |
Wednesday, June 10, 2015 8:24AM - 8:36AM |
G6.00003: Experimental studies of collective excitations of a BEC in light-induced gauge fields Chuan-Hsun Li, Robert Niffenegger, David Blasing, Abraham Olson, Yong P. Chen We present our experimental studies of collective modes including spin dipole mode and scissors mode of a $^{\mathrm{87}}$Rb Bose-Einstein condensate (BEC) in the presence of Raman light-induced gauge fields and synthetic spin-orbit coupling (SOC). By Raman dressing the m$_{\mathrm{f}}$ spin states within the F$=$1 manifold, we engineer atoms' energy-momentum dispersion to create synthetic SOC, and spin dependent synthetic electric and magnetic fields. We have used spin dependent synthetic electric fields to make two BECs with different spins oscillate and collide in the optical trap. We have studied the effects of SOC on both the momentum damping and thermalization behaviors of the BECs when undergoing such spin dipole oscillations. We have also used spatially dependent synthetic electric fields to excite the scissors mode, which has been used as a probe for superfluidity. We have investigated the effects of the synthetic gauge fields and SOC on the measured scissors mode [Preview Abstract] |
Wednesday, June 10, 2015 8:36AM - 8:48AM |
G6.00004: Spin-orbit coupling in periodically driven optical lattices Julian Struck, Juliette Simonet, Klaus Sengstock The realization of artificial spin-orbit coupling (SOC) for the external degrees of freedom of neutral, ultracold atoms has raised considerable interest in recent years. It has been predicted that the interplay between interactions and SOC leads to a variety of many-body phases, ranging from stripe states to topological superfluids. Currently, a main experimental obstacle in the realization of these phases is the limited lifetime of the atomic ensemble. All of the experimentally implemented schemes rely on the near-resonant Raman coupling of internal states and thus suffer from the spontaneous emission of photons, leading to excitations and particle loss. Here we present a novel method for the emulation of artificial SOC for atoms trapped in a tight-binding lattice. This scheme does not involve near-resonant laser fields, avoiding the heating processes connected to spontaneous emission. In our case, the necessary spin-dependent tunnel matrix elements are generated by a rapid, spin-dependent, periodic force, which can be described in the framework of an effective, time-averaged Hamiltonian. An additional radio-frequency coupling between the spin states leads to a mixing of the spin bands. The strength of the SOC can be continuously tuned, simply by adjusting the driving amplitude. [Preview Abstract] |
Wednesday, June 10, 2015 8:48AM - 9:00AM |
G6.00005: Observation of chiral edge states with fermionic atoms in a synthetic Hall ribbon Guido Pagano, Marco Mancini, Giacomo Cappellini, Lorenzo Livi, Carlo Sias, Jacopo Catani, Marie Rider, Marcello Dalmonte, Peter Zoller, Massimo Inguscio, Leonardo Fallani Edge states are a direct manifestation of the effects of topology in fermionic many-body systems. A prominent example is the quantum Hall effect, where chiral edge states are responsible for basic phenomena such as quantized transport. Neutral ultracold fermionic atoms offer a complementary platform to condensed-matter experiments thanks to the high degree of control and tunability over all microscopic parameters. Here we report on the experimental realization of chiral edge states in an ultracold gas of neutral fermions subjected to an effective gauge field. The atoms are confined in a ribbon geometry, with a lattice structure and a tunable width that is provided by a finite-sized ``synthetic'' dimension encoded in the atomic spin. In particular, by imaging individual sites along this synthetic dimension, we detect the existence of chiral edge states and we investigate the breakdown of chirality as a function of the bulk-edge and edge-edge couplings. Our work paves the way towards the investigation of the resilience of chirality against controlled perturbations and to the observation of new topological states of fermionic matter in otherwise inaccessible regimes. [Preview Abstract] |
Wednesday, June 10, 2015 9:00AM - 9:12AM |
G6.00006: Tunable spin-orbit coupling with a periodically driven gradient magnetic field Xinyu Luo, Lingna Wu, Jiyao Chen, Qing Guan, Kuiyi Gao, Zhi-Fang Xu, Li You, Ruquan Wang We report the observation of tunable spin-orbit coupling (SOC) in spin-1 atoms synthesized with a periodically driven gradient magnetic field. Different from all previous experiments which demonstrated synthesized SOC with Raman coupling lasers, the scheme we verify uses only magnetic field, thus could avoid the heating from atomic spontaneous emission in the Raman scheme. The strength of SOC we implemented can be tuned, and the effect of SOC is observed through studying a) the collective dipole oscillation in a harmonic trap after we abruptly turn on SOC, and b) the adiabatically adjusted equilibrium state when we slowly ramp up SOC strength. Our experiment reveals excellent coherence properties for tunable SOC synthesized in atomic condensate through coherent driving gradient magnetic fields. It opens a new avenue for synthesized gauge field aimed at quantum simulation studies with cold atoms. [Preview Abstract] |
Wednesday, June 10, 2015 9:12AM - 9:24AM |
G6.00007: Exploring spin-orbit coupling in a non-degenerate optical lattice clock. Michael L. Wall, Andrew P. Koller, Shuming Li, Ana Maria Rey Optical lattice clocks have progressed in recent years to become not only precise timekeepers, but also sensitive probes of many-body physics. We consider a 1D optical lattice clock in which the wavelength of the laser that interrogates the clock transition is comparable to the optical lattice spacing. This light-matter coupling imprints a spatially dependent phase on the atomic internal state superposition, and this phase can be interpreted as a spin-orbit coupling. We show that this spin-orbit coupling manifests itself in Ramsey spectroscopy as an $s$-wave density shift in otherwise identically prepared fermions, even at temperatures significantly larger than the tunneling. Further, we show that Rabi spectroscopy can be mapped to a Hofstadter model on a two-leg ladder with chiral eigenstates. Using a modified Rabi procedure, we show how to extract momentum-resolved signatures of chirality solely by spectroscopic means. The effects of finite temperature, gaussian transverse confinement, and non-separability between transverse and axial degrees of freedom are discussed. [Preview Abstract] |
Wednesday, June 10, 2015 9:24AM - 9:36AM |
G6.00008: Cavity-assisted spin-orbit coupling in cold atoms Chuanzhou Zhu, Lin Dong, Han Pu We investigate dynamical and static properties of ultracold atoms confined in an optical cavity, where two photon Raman process induces effective coupling between atom's pseudo-spin and center-of-mass momentum. In the meantime, atomic dynamics exerts a back action to cavity photons. We adopt both mean field and master equation approach to tackle the problem and found surprising modifications to atomic dispersions and dynamical instabilities, arising from the intrinsic nonlinearity of the system. Correspondence between semi-classical and quantum limits is analyzed as well. [Preview Abstract] |
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