Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N6: Recent Work on Strongly-coupled Fermi Gases II |
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Sponsoring Units: DAMOP Chair: Allan Griffin, University of Toronto Room: LACC 502A |
Wednesday, March 23, 2005 8:00AM - 8:36AM |
N6.00001: What do we know about the state of cold fermions in the unitary regime? Invited Speaker: A gas of interacting fermions is in the unitary regime if the average separation between particles is large compared to their size, but small compared to their scattering length. Until recently the only physical realization was perhaps in neutron stars, but now experiments with trapped atoms have brought these unique systems into the laboratory. Such gases are strongly interacting many-body systems. From the theoretical point of view the properties of a fermion system in the unitary regime are remarkable, often being referred to as universal. Such a system is at the crossroad between a fermion and a boson superfluids, or what is called the BCS to BEC crossover. From the experimental point of view the fact that basically all parameters of such a system can be tunned essentially at will make these systems unique in physics, realizing for the first time many thought experiments envisioned by theorists over the years. The theorists are at the verge at describing fully and extremely accurately from first principles the properties of these strongly interacting many fermion systems. Many of the experimental results obtained so far are consistent with the theoretical expectation that these systems are superfluid. However, the existence of a superflow as such has not been put in evidence in experiments, yet! In this talk I shall review the basic experimental results obtained so far and confront them with our most detailed theoretical description available at this time. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 9:12AM |
N6.00002: Scattering properties of weakly-bound dimers of Fermi atoms Invited Speaker: We discuss the behavior of weakly bound bosonic dimers formed in a two-component Fermi gas with a large positive scattering length for the interspecies interaction. We present a theoretical approach for solving a few-body scattering problem and describe the physics of dimer-dimer elastic and inelastic scattering. We explain why these diatomic molecules, while in the highest ro-vibrational level, are characterized by remarkable collisional stability. \newline \newline Co-authors are Christophe Salomon, LKB, Ecole Normale Superieure, Paris, France; Georgy Shlyapnikov, LPTMS, University of South Paris, Orsay, France. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:48AM |
N6.00003: Quantum Monte Carlo study of a Fermi gas in the BCS-BEC crossover Invited Speaker: We calculate the equation of state of a two-component Fermi gas with attractive short-range interspecies interactions using the fixed-node diffusion Monte Carlo method. The interaction strength is varied over a wide range by tuning the value $a$ of the $s$-wave scattering length of the two-body potential. For $a>0$ and $a$ smaller than the inverse Fermi wavevector our results show a molecular regime with repulsive interactions well described by the dimer-dimer scattering length $a_m=0.6 a$. The momentum distribution of atoms, the pair correlation functions and the condensate fraction of pairs are discussed as a function of the interaction strength. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:24AM |
N6.00004: Observation of the pairing gap in a strongly interacting Fermi gas Invited Speaker: We study fermionic pairing in an ultracold two-component gas of lithium-6 atoms by observing an energy gap in the radio-frequency excitation spectra. With control of the two-body interactions through a Feshbach resonance, we demonstrate the dependence of the pairing gap on coupling strength, temperature, and Fermi energy. The appearance of an energy gap with moderate evaporative cooling suggests that our full evaporation brings the strongly interacting system deep into a superfluid state. [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 11:00AM |
N6.00005: Spectroscopic studies of superfluid atomic Fermi gases Invited Speaker: We consider trapped atomic Fermi gases with Feshbach-resonance enhanced interactions in temperatures below and above the superfluid critical temperature. We analyze the spectrum of RF(or laser)-excitations for transitions that transfer atoms out of the superfluid state, and compare the results with recent experiments, both at the unitarity regime where a pseudogap is likely and away from it. We also analyze other spectroscopic signatures of pairing, e.g. in optical lattices. [Preview Abstract] |
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