The inverse-square interaction phase diagram: unitarity in the bosonic ground state

TL;DR

This paper investigates the ground-state properties of bosons with inverse-square interactions, revealing a phase transition and providing analytical and numerical insights into their behavior at unitarity, with implications for stable Bose systems.

Contribution

The study introduces a comprehensive analysis combining analytical approaches and diffusion Monte Carlo simulations to characterize the inverse-square bosonic system at unitarity, including phase transition insights.

Findings

Identification of a gas-solid phase transition as a function of interaction strength.

Development of a Padé approximant fitting numerical data across interaction regimes.

Confirmation of plasmon excitations in both phases and agreement with theoretical models.

Abstract

Ground-state properties of bosons interacting via inverse square potential (three dimensional Calogero-Sutherland model) are analyzed. A number of quantities scale with the density and can be naturally expressed in units of the Fermi energy and Fermi momentum multiplied by a dimensionless constant (Bertsch parameter). Two analytical approaches are developed: the Bogoliubov theory for weak and the harmonic approximation (HA) for strong interactions. Diffusion Monte Carlo method is used to obtain the ground-state properties in a non-perturbative manner. We report the dependence of the Bertsch parameter on the interaction strength and construct a Pad\'e approximant which fits the numerical data and reproduces correctly the asymptotic limits of weak and strong interactions. We find good agreement with beyond-mean field theory for the energy and the condensate fraction. The pair distribution function and the static structure factor are reported for a number of characteristic interactions. We demonstrate that the system experiences a gas-solid phase transition as a function of the dimensionless interaction strength. A peculiarity of the system is that by changing the density it is not possible to induce the phase transition. We show that the low-lying excitation spectrum contains plasmons in both phases, in agreement with the Bogoliubov and HA theories. Finally, we argue that this model can be interpreted as a realization of the unitary limit of a Bose system with the advantage that the system stays in the genuine ground state contrarily to the metastable state realized in experiments with short-range Bose gases.