Path integral Monte Carlo study of a doubly dipolar Bose gas

Abstract

By combining first-principles path integral Monte Carlo methods and mean-field techniques, we explore the properties of cylindrically trapped doubly dipolar Bose gases. We first verify the emergence of a pancake quantum droplet at low temperatures, validating previous mean-field calculations. In a regime of small doubly dipolar interactions, first-principles calculations agree with the generalized Gross-Pitaevskii equation. Such an accordance disappears in a large interaction limit. Here the path integral Monte Carlo method estimates the strong doubly dipolar regime with accuracy. In contrast, the Gross-Pitaevskii equation does not seize quantum fluctuations in full. We also provide a complete description of the system's quantum behavior in a wide range of parameters. When the system forms a droplet, the superfluid fraction exhibits an anisotropic behavior if compared to the usual Bose gas regime. Interestingly, we observe that the transition temperature from thermal gas to droplet is higher than that of the thermal gas to a Bose-Einstein condensate, indicating the robustness of the droplet against thermal fluctuations. Further, we investigate the anisotropic behavior of the superfluid fraction during the structural transition from a pancake to a cigar-shaped droplet by varying the ratio between electric and magnetic dipole interaction strengths. Our findings furnish evidence that the stability of doubly dipolar Bose-Einstein condensates can be detected in experiments by means of dysprosium atoms.