Phonon Stability and Sound Velocity of Quantum Droplets in a Boson Mixture

Abstract

Quantum droplets have been realized in experiments on binary boson mixtures and dipolar Bose gases. In these systems, the mean-field energy of the Bose-Einstein condensation is attractive, and the repulsive Lee-Huang-Yang energy is crucial for stability. The Bogoliubov theory incorrectly predicts that the phonon mode is dynamically unstable in the long-wavelength limit. In this work, we go beyond the Bogoliubov theory to study how the phonon mode is stabilized in the quantum droplet of a binary boson mixture. Similar to Beliaev's approach to a single-component Bose gas, we compute higher-order contributions to the self-energy of the boson propagator. We find that the interaction between spin and phonon excitations is the key for the phonon stability. We obtain the sound velocity which can be tested by measuring the superfluid critical velocity of the droplet in experiments. Beliaev damping of this quantum droplet is also discussed.

5 pages, 2 figures

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• Phonon Stability of Quantum Droplets in a dipolar Bose gases
• Droplet under confinement: Competition and coexistence with soliton bound state
• Quantum Criticality of Liquid-Gas Transition in a Binary Bose Mixture
• The Effective Single-mode model of a Binary Boson Mixture in the Quantum Droplet Region
• First-order Bose-Einstein condensation with three-body interacting bosons
• Hydrodynamics of multi-component Bosonic systems
• Spinor Boson Droplets Stabilized By Spin Fluctuations
• Polarized Rabi-Coupled and Spinor Boson Droplets
• Breakdown of the single-mode description of ultradilute quantum droplets in binary Bose mixtures: A perspective from a microscopic bosonic pairing theory
• One-dimensional asymmetrically interacting quantum droplets in Bose-Bose mixtures
• Bose-Bose gases with nonuniversal corrections to the interactions: a droplet phase
• Nonuniversal equation of state for Rabi-coupled bosonic gases: a droplet phase
• Phases and dynamics of an impurity immersed in one-dimensional quantum droplets