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arXiv:1810.01795 · Physical Review A

Phase-separation dynamics induced by an interaction quench of a correlated Fermi-Fermi mixture in a double well

J. Erdmann, S. I. Mistakidis, Peter Schmelcher

Published Jan 3, 2019• 41 citations
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Abstract

We explore the interspecies interaction quench dynamics of ultracold spin-polarized few-body mass-balanced Fermi-Fermi mixtures confined in a double well with an emphasis on the beyond Hartree-Fock correlation effects. It is shown that the ground state of particle-imbalanced mixtures exhibits a symmetry breaking of the single-particle density for strong interactions in the Hartree-Fock limit, which is altered within the many-body approach. Quenching the interspecies repulsion towards the strongly interacting regime, the two species phase separate within the Hartree-Fock approximation while remaining miscible in the many-body treatment. Despite their miscible character on the one-body level, the two species are found to be strongly correlated and exhibit a phase separation on the two-body level that suggests the antiferromagneticlike behavior of the few-body mixture. For particle-balanced mixtures we show that an intrawell fragmentation (filamentation) of the density occurs both for the ground state and upon quenching from weak to strong interactions, a result that is exclusively caused by the presence of strong correlations. By inspecting the two-body correlations, a phase separation of the two species is unveiled, being a precursor towards an antiferromagnetic state. Finally, we simulate in situ single-shot measurements and showcase how our findings can be retrieved by averaging over a sample of single-shot images.

DOI
10.1103/physreva.99.013605

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We explore the interspecies interaction quench dynamics of ultracold spin-polarized few-body mass-balanced Fermi-Fermi mixtures confined in a double well with an emphasis on the beyond Hartree-Fock correlation effects. It is shown that the ground state of particle-imbalanced mixtures exhibits a symmetry breaking of the single-particle density for strong interactions in the Hartree-Fock limit, which is altered within the many-body approach. Quenching the interspecies repulsion towards the strongly interacting regime, the two species phase separate within the Hartree-Fock approximation while remaining miscible in the many-body treatment. Despite their miscible character on the one-body level, the two species are found to be strongly correlated and exhibit a phase separation on the two-body level that suggests the antiferromagneticlike behavior of the few-body mixture. For particle-balanced mixtures we show that an intrawell fragmentation (filamentation) of the density occurs both for the ground state and upon quenching from weak to strong interactions, a result that is exclusively caused by the presence of strong correlations. By inspecting the two-body correlations, a phase separation of the two species is unveiled, being a precursor towards an antiferromagnetic state. Finally, we simulate in situ single-shot measurements and showcase how our findings can be retrieved by averaging over a sample of single-shot images.
We unravel the correlated tunneling dynamics of a mass imbalanced few-body Fermi-Fermi mixture upon quenching the tilt of a double well. The nonequilibrium dynamics of both species changes from Rabi oscillations close to the noninteracting limit to a delayed tunneling dynamics for moderate interspecies repulsions. Considering strong interspecies interactions, the lighter species experiences quantum self-trapping due to the heavier species which acts as an effective material barrier, while performing almost perfect Rabi oscillations. The degree of entanglement, inherent in the system, is analyzed and found to be significant at both moderate and strong repulsions. To relate our findings to possible experimental realizations, we simulate in situ single-shot measurements and discuss how a sampling of such images dictates the observed dynamics. Finally, the dependence of the tunneling behavior on the mass ratio, the particle number in each species, and the height of the barrier of the double well is showcased.
We explore the quench dynamics of a binary Bose–Einstein condensate crossing the miscibility–immiscibility threshold and vice versa, both within and in particular beyond the mean-field approximation. Increasing the interspecies repulsion leads to the filamentation of the density of each species, involving shorter wavenumbers and longer spatial scales in the many-body (MB) approach. These filaments appear to be strongly correlated and exhibit domain-wall structures. Following the reverse quench process multiple dark–antidark solitary waves are spontaneously generated and subsequently found to decay in the MB scenario. We simulate single-shot images to connect our findings to possible experimental realizations. Finally, the growth rate of the variance of a sample of single-shots probes the degree of entanglement inherent in the system.
We investigate the nonequilibrium quantum dynamics of one and two heavy fermionic impurities being harmonically trapped and repulsively interacting with a finite ensemble of majority fermions. A quench of the potential of the majority species from a double-well to a harmonic trap is applied, enforcing its counterflow, which in turn perturbs the impurities. For weak repulsions, it is shown that the mixture undergoes a periodic mixing and demixing dynamics, while stronger interactions lead to a more pronounced dynamical spatial separation. In the presence of correlations, the impurity exhibits an expansion dynamics which is absent in the Hartree-Fock case, resulting in an enhanced degree of miscibility. We generalize our results to different impurity masses and demonstrate that the expansion amplitude of the impurity reduces for a larger mass. Furthermore, we showcase that the majority species is strongly correlated and a phase separation occurs on the two-body level. Most importantly, signatures of attractive impurity-impurity induced interactions mediated by the majority species are identified in the time evolution of the two-body correlations of the impurities, a result that is supported by inspecting their spatial size.
We unravel the nonequilibrium dynamics of two fermionic impurities immersed in a one-dimensional bosonic gas following an interspecies interaction quench. Monitoring the temporal evolution of the single-particle density of each species we reveal the existence of four distinct dynamical regimes. For weak interspecies repulsions both species either perform a breathing motion or the impurity density splits into two parts which interact and disperse within the bosonic cloud. Turning to strong interactions we observe the formation of dark-bright states within the mean-field approximation. However, the correlated dynamics shows that the fermionic density splits into two repelling density peaks which either travel toward the edges of the bosonic cloud where they equilibrate or they approach an almost steady state propagating robustly within the bosonic gas which forms density dips at the same location. For these strong interspecies interactions an energy transfer process from the impurities to their environment occurs at the many-body level, while a periodic energy exchange from the bright states (impurities) to the bosonic species is identified in the absence of correlations. Finally, inspecting the one-body coherence function for strong interactions enables us to draw conclusions on the spatial localization of the quench-induced fermionic density humps.
We explore the tunneling dynamics of strongly correlated bosonic mixtures in a one-dimensional double well. The roles of the inter- and intraspecies interactions and their interplay are investigated using the numerically exact multiconfiguration time-dependent Hartree (MCTDH) method. The dynamics is studied for three initial configurations: complete and partial population imbalance and a species-separated state. Increasing the interspecies interaction leads to a strong increase of the tunneling time period analogous to the quantum self-trapping for condensates. The intraspecies repulsion can suppress or enhance the tunneling period depending on the strength of the interspecies correlations as well as the initial configuration. Completely correlated tunneling between the two species and within the same species as well as mechanisms of species separation and counterflow are revealed. These effects are explained by studying the few-body energy spectra as well as the properties of the contributing stationary states.
We unravel the correlated nonequilibrium dynamics of a mass balanced Bose-Fermi mixture in a one-dimensional optical lattice upon quenching an imposed harmonic trap from strong to weak confinement. Regarding the system's ground state, the competition between the inter- and intraspecies interaction strength gives rise to the immiscible and miscible phases characterized by negligible and complete overlap of the constituting atomic clouds, respectively. The resulting dynamical response depends strongly on the initial phase and consists of an expansion of each cloud and an interwell tunneling dynamics. For varying quench amplitude and referring to a fixed phase, a multitude of response regimes is unveiled, being richer within the immiscible phase, which are described by distinct expansion strengths and tunneling channels.