Phonon Stability of Quantum Droplets in a dipolar Bose gases

TL;DR

This paper investigates the phonon stability of dipolar quantum droplets in Bose gases, demonstrating that quantum fluctuations can enhance stability and providing anisotropic sound velocity predictions for experimental validation.

Contribution

It applies the Beliaev formalism to analyze phonon energies, showing quantum fluctuations improve stability in dipolar quantum droplets, extending previous Bogoliubov theory results.

Findings

Quantum fluctuations enhance phonon stability.

Anisotropic sound velocity predicted for experiments.

Phonon energies are stabilized by higher-order quantum effects.

Abstract

Stabilized by quantum fluctuations, dipolar Bose-Einstein condensates can form self-bound liquidlike droplets in the mean-field unstable regime. However in the Bogoliubov theory, some phonon energies are imaginary in the long-wavelength limit, implying dynamical instability of this system. A similar instability appears in the Bogoliubov theory of a binary quantum droplet, and is removed due to higher-order quantum fluctuations as shown recently [1]. In this work, we study the phonon energy of a dipolar quantum droplet in the Beliaev formalism, and find that quantum fluctuations can enhance the phonon stability. We obtain the anisotropic sound velocity which can be tested in experiment.