Self-bound droplet clusters in laser-driven Bose-Einstein condensates

TL;DR

This paper demonstrates how optically driven Bose-Einstein condensates can form self-bound droplet crystals with tunable interactions, leading to diverse stable lattice structures without external confinement.

Contribution

It introduces a method to control long-range atomic interactions in BECs via optical feedback, resulting in novel self-bound droplet crystal states with various lattice geometries.

Findings

Formation of self-bound quantum droplet crystals with different lattice structures.

Control over interaction sign and strength through optical elements.

Stable, self-bound states without external trapping.

Abstract

We investigate a two-dimensional Bose-Einstein condensate that is optically driven via a retro-reflecting mirror, forming a single optical feedback loop. This induces a peculiar type of long-range atomic interaction with highly oscillatory behavior, and we show here how the sign of the underlying interaction potential can be controlled by additional optical elements and external fields. This additional tunability enriches the behavior of the system substantially, and gives rise to a surprising range of new ground states of the condensate. In particular, we find the emergence of self-bound crystals of quantum droplets with various lattice structures, from simple and familiar triangular arrays to complex superlattice structures and crystals with entirely broken rotational symmetry. This includes mesoscopic clusters composed of small numbers of quantum droplets as well as extended crystalline structures. Importantly, such ordered states are entirely self-bound and stable without any external in-plane confinement, having no counterpart to other quantum-gas settings with long-range atomic interactions.