Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session B1: Invited Session: Synthetic Gauge Fields in Quantum Gases |
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Chair: Congjun Wu, University of California, San Diego Room: Grand Ballroom BCD |
Tuesday, June 5, 2012 10:30AM - 11:00AM |
B1.00001: Light induced gauge fields and spin orbital coupling in cold atomic gas Invited Speaker: Ian Spielman Here I present our experimental work synthesizing gauge fields for Bose-Einstein condensates (BECs). I will first summarize our earlier work creating a scalar (abelian) gauge field (akin to the electromagnetic vector potential) and then focus in detail our current work creating a matrix valued (although still abelian) gauge field. I will discuss this gauge field in the language of spin-orbit coupling where it consists of an equal sum of Rashba and Dresselhaus couplings. Specifically, we couple two internal states of rubidium 87 with a pair of ``Raman'' lasers and load our BEC into the resulting adiabatic eigenstates. In agreement with theory, we observe that below a critical coupling strength our BEC has well defined spin degrees of freedom and acts like a spin-orbit-coupled spin-1/2 Bose gas. As a function of the Raman laser strength, a new exchange-driven interaction between the two dressed spins develops, which drives a (quantum) phase transition from a state where the two dressed spin states spatially mix, to one where they phase separate. Our 3D mean field theory accurately locates the critical laser strength for this transition. Going beyond this simple modification to the spin-dependent interaction, we show that in the limit of large laser intensity, the particles act as free atoms, but interact with contributions from higher even partial waves. [Preview Abstract] |
Tuesday, June 5, 2012 11:00AM - 11:30AM |
B1.00002: Experimental realization of spin-orbit coupling in degenerate Fermi gas Invited Speaker: Jing Zhang We report the first experimental realization of SO coupled degenerate Fermi gas. Evidences of spin-orbit coupling have been obtained from the Raman Rabi oscillation and the spin-dependent momentum distribution asymmetry. We also find that the momentum distribution in helical bases is consistent with topological changes of Fermi surfaces. In the near future, we plan to bring the system close to a Feshbach resonance where the s-wave interaction become strongly attractive. This progress enables us to study stronger pairing and higher Tc enhanced by SO coupling in resonant interacting Fermi gases and topological insulator and topological superfluid in a more flexible setup in near future. [Preview Abstract] |
Tuesday, June 5, 2012 11:30AM - 12:00PM |
B1.00003: Topological quantum criticality in spin-orbit coupled fermions Invited Speaker: Sumanta Tewari Spin-orbit coupled fermions offer a fascinating playground for realizing interesting topological quantum phases and the associated quantum critical phenomena. In two dimensions and in the presence of an attractive s-wave pairing interaction and a Zeeman field, spin-orbit coupled fermions can condense into a fully gapped non-Abelian topological superfluid phase separated from a conventional s-wave superfluid phase by a topological quantum phase transition. The critical point for this transition is marked by the proliferation of gapless nodal quasiparticles which can be tracked by studying the momentum-resolved excitation spectrum from the center of the Brillouin zone. In three dimensions the same system goes through a series of topological quantum transitions with increasing Zeeman field and the low energy excitations in some of these phases realize the long-sought low-temperature analog of Weyl fermions of particle physics. In this talk I will describe in some detail the interesting topological phases and the associated quantum criticality that can be realized using spin-orbit coupled fermions in cold atom systems. [Preview Abstract] |
Tuesday, June 5, 2012 12:00PM - 12:30PM |
B1.00004: Spin-Orbit Coupled Quantum Gases Invited Speaker: Hui Zhai In this talk I will discuss both spin-orbit coupled Bose condensate and degenerate Fermi gases. In the first part of this talk, I will discuss bosons with Rashba type spin-orbit coupling. We find the ground state exhibits two distinct non-trivial phases: the plane wave phase and the stripe superfluid phase. And the finite temperature thermal fluctuations can lead to an even more interesting boson paired superfluid state with half vortices. I will further discuss collective mode of spin-orbit coupled condensate. We find the dipole modes of a BEC is no longer harmonic due to the non-abelian nature of the gauge potential, and there will be a magnetization oscillation synchronized to the dipole motion due to the absence of Galilean invariance. Macroscopic quantum tunneling will also take place during the dipole oscillation. In the second part of this talk, I will discuss degenerate Fermi gases and the BEC-BCS crossover with spin-orbit coupling. I will talk about spin dephasing and interaction effects in the Raman induced spin dynamics, and the topological change of Fermi surfaces. I will emphasize that Rashba spin-orbit coupling can significantly enhance the pairing strength and the superfluid transition temperature. [Preview Abstract] |
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