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Communications in Theoretical Physics

Macroscopic squeezing in quasi-one-dimensional two-component Bose gases

Yaoqi Tian, Junqiao Pan, Tao Shi, Su Yi

Published Oct 19, 2023• 1 citation
Publisher

Abstract

Abstract We investigate the ground-state properties and the dynamics of quasi-one-dimensional quantum droplets of binary Bose condensates by employing the Gaussian state theory. We show that there exists three quantum phases for the ground states of the droplets, including a coherent state and two macroscopic squeezed states. The phase transition between two macroscopic squeezed states is of the third order; while between the macroscopic squeezed state and the coherent is of a crossover type. As for the dynamics, we find that, by tuning the reduced scattering length to a negative value, a significant fraction of the atoms can be transferred from a coherent state to a macroscopic squeezed state. Our studies open up the possibility of generating macroscopic squeezed states using binary condensates.

DOI
10.1088/1572-9494/ad04ce

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Abstract We investigate the ground-state properties and the dynamics of quasi-one-dimensional quantum droplets of binary Bose condensates by employing the Gaussian state theory. We show that there exists three quantum phases for the ground states of the droplets, including a coherent state and two macroscopic squeezed states. The phase transition between two macroscopic squeezed states is of the third order; while between the macroscopic squeezed state and the coherent is of a crossover type. As for the dynamics, we find that, by tuning the reduced scattering length to a negative value, a significant fraction of the atoms can be transferred from a coherent state to a macroscopic squeezed state. Our studies open up the possibility of generating macroscopic squeezed states using binary condensates.
We systematically investigate the ground-state properties of self-bound droplets of quasi-two-dimensional binary Bose gases by using the Gaussian state theory. We find that quantum droplets consists of two macroscopic squeezed phases and a macroscopic coherent phase. We map out the phase diagram and determine all phase boundaries via both numerical and nearly analytical methods. In particular, we find three easily accessible signatures for the quantum phases and the stabilization mechanism of the self-bound droplets by precisely measuring their radial size. Our studies indicate that binary droplets represent an ideal platform for in-depth investigations of the quantum nature of the droplet state.
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Abstract Explicit realization of quantum droplets, even and odd Schrödinger cat-like states is demonstrated in an atom-molecular Bose-Einstein condensate in the presence of interconversion and Kerr non-linear interactions. The crucial roles of both the χ2-type nonlinearity and chemical potential in the formation of these macroscopic quantum states are shown, where the atomic condensate is in the cat-like state, with the corresponding molecular wave packet being a quantum droplet. The physical mechanism for their creation and common origin is established to be the non-linearity-induced self-trapping potentials, governed by photoassociation or Feshbach resonance, with the Kerr-type nonlinearities playing subdominant roles. The coexisting and controllable atom and molecular droplets are shown to realize the atom-molecular squeezed state with profiles ranging from Gaussian to flat-top super-Gaussian form. The Wigner functions are exhibited revealing the cat-like states' phase space interference and squeezing of droplets.
Within the framework of the Gaussian-state theory, we show that the quantum many-body ground state of a trapped condensate with weakly attractive interaction is a single-mode squeezed vacuum state, as oppose to the coherent state under repulsive interaction. The spatial mode of the squeezed-state condensates satisfies a Gross-Pitaevskii like equation in which the interaction strength is augmented by a factor 333 due to the large particle fluctuation of the squeezed state. We also study the collective excitations of the condensates by the tangential space projection, which leads to new two-particle excitations and confirms the phase transition from coherent-state to squeezed-state condensates. Our investigation clarifies the quantum states of the attractive condensates and will shed new light on research of the droplet phases in dipolar and multicomponent condensates.
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