Austen Lamacraft

Potential Insights into Nonequilibrium Behavior from Atomic Physics

Abstract This chapter seeks to outline a few basic problems in quantum statistical physics, where recent experimental advances from the atomic physics community offer the hope of dramatic progress. The focus is on nonequilibrium situations, where the powerful concepts and methods of equilibrium statistical physics and “linear response” theory (for small deviations from equilibrium) are not applicable. The problems discussed here are chosen in part because they have a high degree of “universality” or generality across different microscopic situations, as the major challenge in nonequilibrium statistical physics, both quantum and classical, has been to find principles as general as the basic principles of equilibrium statistical physics or linear response.

Critical velocity of a mobile impurity in one-dimensional quantum liquids

We study the notion of superfluid critical velocity in one spatial dimension. It is shown that, for heavy impurities with mass M exceeding a critical mass Mc, the dispersion develops periodic metastable branches resulting in dramatic changes of dynamics in the presence of an external driving force. In contrast to smooth Bloch oscillations for M<Mc, a heavy impurity climbs metastable branches until it reaches a branch termination point or undergoes a random tunneling event, both leading to an abrupt change in velocity and an energy loss. This is predicted to lead to a nonanalytic dependence of the impurity drift velocity on small forces.

Radio Frequency Spectroscopy of a Strongly Imbalanced Feshbach-Resonant Fermi Gas

A su!ciently large species imbalance (polarization) in a tw o-component Feshbach resonant Fermi gas is known to drive the system into its normal state. We show that the resulting stronglyinteracting state is a conventional Fermi liquid, that is, however, strongly renormalized by pairing fluctuations. Using a controlled 1/N expansion, we calculate the properties of this state with a particular emphasis on the atomic spectral function, the momentum distribution functions displaying the Migdal discontinuity, and the radio frequency (RF) spectrum. We discuss the latter in the light of the recent experiments of Schunck et al. (Science 316, 867 (2007)) on such a resonant Fermi gas, and show that the observations are consistent with a conventional, but strongly renormalized Fermi-liquid picture. PACS numbers: 67.85.De, 03.75.Kk, 03.75.Ss

Long-wavelength spin dynamics of ferromagnetic condensates

We obtain the equations of motion for a ferromagnetic Bose condensate of arbitrary spin in the long-wavelength limit. We find that the magnetization of the condensate is described by a nontrivial modification of the Landau-Lifshitz equation, in which the magnetization is advected by the superfluid velocity. This hydrodynamic description, valid when the condensate wave function varies on scales much longer than either the density or spin healing lengths, is physically more transparent than the corresponding time-dependent Gross-Pitaevskii equation. We discuss the conservation laws of the theory and its application to the analysis of the stability of magnetic helices and Larmor precession. Precessional instabilities, in particular, provide a novel physical signature of dipolar forces.

Dispersion relation and spectral function of an impurity in a one-dimensional quantum liquid

We consider the motion of an impurity particle in a general one-dimensional quantum fluid at zero temperature. The dispersion relation

Spinodal decomposition in polarized Fermi superfluids

Omega(P)

Low-energy dynamics of spinor condensates

of the impurity is strongly affected by interactions with the fluid as the momentum approaches

Diffractive scattering of three particles in one dimension: A simple result for weak violations of the Yang-Baxter equation

pmpihbar n, pm 3pihbar n, ...

Spin-1 microcondensate in a magnetic field

, where

Noise correlations in the expansion of an interacting 1D Bose gas from a regular array

n