Pure Goldstone mode in the quench dynamics of a confined ultracold Fermi gas in the BCS-BEC crossover regime

Abstract

We present a numerical study of the dynamic response of a confined superfluid Fermi gas to a rapid change of the scattering length (i.e., an interaction quench). Based on a fully microscopic time-dependent density-matrix approach within the full Bogoliubov-de Gennes formalism that includes a 3D harmonic confinement we simulate and identify the emergence of a Goldstone mode of the BCS gap in a cigar-shaped ${}^6$Li gas. By analyzing this Goldstone mode over a wide range of parameters, we show that its excitation spectrum is gapless and that its main frequency is not fixed by the trapping potential but that it is determined by the details of the quench. Thus, we report the emergence of a pure Goldstone mode of the BCS gap that --in contrast to situations in many previous studies-- maintains its gapless excitation spectrum predicted by the Goldstone theorem. Furthermore, we observe that the size-dependent superfluid resonances resulting from the atypical BCS-BEC crossover have a direct impact on this Goldstone mode. Finally, we find that the interaction quench-induced Goldstone mode leads to a low-frequency in-phase oscillation of the single-particle occupations with complete inversion of the lowest-lying single-particle states which could provide a convenient experimental access to the pure gapless Goldstone mode.

This article supersedes our previous publication arXiv:1511.04239 [cond-mat.quant-gas]

References in corpus (18)

• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
• Collective excitations of a degenerate gas at the BEC-BCS crossover
• Using photoemission spectroscopy to probe a strongly interacting Fermi gas
• Amplitude / Higgs Modes in Condensed Matter Physics
• The `Higgs' Amplitude Mode at the Two-Dimensional Superfluid-Mott Insulator Transition
• Verification of universal relations in a strongly interacting Fermi gas
• Precision Measurements of Collective Oscillations in the BEC-BCS Crossover
• Synchronization in the BCS Pairing Dynamics as a Critical Phenomenon
• Collective modes and ballistic expansion of a Fermi gas in the BCS-BEC crossover
• Detecting the Amplitude Mode of Strongly Interacting Lattice Bosons by Bragg Scattering
• Quantum quench phase diagrams of an s-wave BCS-BEC condensate
• Collective oscillations of a Fermi gas in the unitarity limit: Temperature effects and the role of pair correlations
• Dynamics of a strongly interacting Fermi gas: the radial quadrupole mode
• Atypical BCS-BEC crossover induced by quantum-size effects
• Spectroscopic signatures of nonequilibrium pairing in atomic Fermi gases
• A long-lived Higgs mode in a two-dimensional confined Fermi gas
• Temperature and finite-size effects in collective modes of superfluid Fermi gases