One-dimensional asymmetrically interacting quantum droplets in Bose-Bose mixtures

TL;DR

This paper provides a theoretical analysis of one-dimensional asymmetric quantum droplets in Bose-Bose mixtures, revealing how interaction asymmetry influences their shape, excitations, and phase behavior, with implications for ultracold atomic experiments.

Contribution

It introduces a detailed theoretical framework for asymmetric quantum droplets, analyzing their density profiles, phase transitions, and collective excitations using extended Gross-Pitaevskii equations.

Findings

Density profile transitions from Gaussian to flat-top with interaction ratio

Breathing mode frequency decreases monotonically with interaction ratio

Spin modes show distinct in-phase and out-of-phase dynamics

Abstract

We theoretically investigate ground-state properties and collective excitations of one-dimensional quantum droplets in asymmetric Bose-Bose mixtures with unequal intraspin interactions. Using the extended Gross-Pitaevskii equation supported by variational and sum-rule methods, we show that the intraspin interaction ratio substantially alters the droplet's density profile, driving a transition from Gaussian-like to flat-top shapes. By examining two experimentally relevant parameter regions, we analyze density profiles, radii, peak densities, and excitation spectra to distinguish quantum phases and to depict phase diagrams in the space of asymmetric interaction ratio and total atom number. We carefully study the frequencies of both well-known dipole and breathing modes and less-explored spin dipole and spin breathing modes. The breathing mode frequency decreases monotonically with interaction ratio, approaching asymptotically the result of a conventional weakly interacting Bose gas. It varies non-monotonically with total atom number, peaking at a critical point that highlights the crucial role of quantum fluctuations. In contrast, spin modes display distinct temporal spin density distributions and reveal in-phase and out-of-phase relative dynamics between components. Their frequencies depend instead monotonically on the interaction ratio and atom number. Our results provide a comprehensive understanding of asymmetric quantum droplets and link to experimentally accessible regimes in ultracold $^{39}$K atomic gases.