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arXiv:2001.04796 · Physical Review Research

Quantum droplets of bosonic mixtures in a one-dimensional optical lattice

Ivan Morera, Grigori E. Astrakharchik, Artur Polls, Bruno Juliá-Díaz

Published Apr 9, 2020• 59 citations
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Abstract

In this paper, the authors demonstrate the existence of quantum droplets in a two-species one dimensional Bose-Hubbard model. The phase diagram of the system is presented and multiple phases are identified. Specifically, in the strongly interacting regime quantum droplets exhibit pair-superfluidity characterized by the appearance of phase coherence of pairs but not of individual atoms.

DOI
10.1103/physrevresearch.2.022008

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In this paper, the authors demonstrate the existence of quantum droplets in a two-species one dimensional Bose-Hubbard model. The phase diagram of the system is presented and multiple phases are identified. Specifically, in the strongly interacting regime quantum droplets exhibit pair-superfluidity characterized by the appearance of phase coherence of pairs but not of individual atoms.
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The zero-temperature phase diagram of a binary mixture of bosonic and fermionic atoms in a one-dimensional optical lattice is studied in the framework of the Bose-Fermi-Hubbard model. By exact numerical solution of the associated eigenvalue problems, ground state observables and the response to an external phase twist are evaluated. The stiffnesses under phase variations provide measures for the boson superfluid fraction and the fermionic Drude weight. Several distinct quantum phases are identified as functions of the strength of the repulsive boson-boson and the boson-fermion interactions. In addition to the bosonic Mott-insulator phase, two other insulating phases are found, where both the bosonic superfluid fraction and the fermionic Drude weight vanish simultaneously. One of these double-insulator phases exhibits a crystalline diagonal long-range order, while the other is characterized by spatial separation of the two species.
We study the phase structure of mixtures of strongly interacting bosonic atoms in a combined potential of a parabolic trap and an optical lattice. We apply a mean-field approximation and a local density approximation to the Bose-Hubbard model for the Bose-Bose mixture, and calculate the superfluid order parameter and the number of particles per site for both species. We find that the mixture is phase-separated due to the strong onsite inter-species repulsion. Considering a zero-hopping limit, we find that the coexisting phase can appear when onsite inter-species repulsion interaction is weak.
The ground state phase diagram of the one-dimensional Bose-Fermi Hubbard model is studied in the canonical ensemble using a quantum Monte Carlo method. We focus on the case where both species have half filling in order to maximize the pairing correlations between the bosons and the fermions. In case of equal hopping we distinguish among phase separation, a Luttinger liquid phase, and a phase characterized by strong singlet pairing between the species. True long-range density waves exist with unequal hopping amplitudes.
We study the ground state phases of Bose-Fermi mixtures in one-dimensional optical lattices with quantum Monte Carlo simulations using the canonical worm algorithm. Depending on the filling of bosons and fermions, and the on-site intra- and interspecies interaction, different kinds of incompressible and superfluid phases appear. On the compressible side, correlations between bosons and fermions can lead to a distinctive behavior of the bosonic superfluid density and the fermionic stiffness, as well as of the equal-time Green functions, which allow one to identify regions where the two species exhibit anticorrelated flow. We present here complete phase diagrams for these systems at different fillings and as a function of the interaction parameters.
We study the ground-state properties of mixtures of strongly interacting bosonic atoms in an optical lattice. Applying a mean-field approximation to the Hubbard model for Bose-Bose mixtures, we calculate the densities and superfluid order parameters for both species. Due to the repulsive interaction between the two species, the system exhibits phase separation. First, in the extreme limit of the zero-hopping case, we derive analytical expressions for the phase boundaries. In particular, we derive the conditions for phase separation in the Mott insulator phase. We find that the conditions for the phase separation depend on the on-site interactions as well as the occupation numbers. In particular, we show that the coexisting state appears by varying the on-site inter-species interaction. We also show the phase diagram of the finite hopping case. Second, we calculate the spatial density profile of 87^{87}87Rb-41^{41}41K mixtures in the combined potential of a parabolic trap and an optical lattice using the local density approximation. We fixed the number of 87^{87}87Rb and varied the number of 41^{41}41K, and used the parameters estimated by experiments. We show that the phase separated 87^{87}87Rb-41^{41}41K mixtures distribute like in a parabolic trap case. Furthermore, we find that phase separated mixtures distribute a nesting structure.