Emergence of a tunable crystalline order in a Floquet-Bloch system from a parametric instability

TL;DR

This paper demonstrates how Floquet engineering can induce tunable crystalline order in a Bose-Einstein condensate via parametric instability, creating metastable exotic states with adjustable density modulations.

Contribution

It introduces a method to generate and control crystalline order in quantum gases using Floquet modulation, revealing new instability-driven phases.

Findings

Density modulation with tunable periodicity observed

Instability regions depend on modulation parameters

Metastable exotic states of matter produced

Abstract

Parametric instabilities in interacting systems can lead to the appearance of new structures or patterns. In quantum gases, two-body interactions are responsible for a variety of instabilities that depend on the characteristics of both trapping and interactions. We report on the Floquet engineering of such instabilities, on a Bose-Einstein condensate held in a time-modulated optical lattice. The modulation triggers a destabilization of the condensate into a state exhibiting a density modulation with a new spatial periodicity. This new crystal-like order directly depends on the modulation parameters: the interplay between the Floquet spectrum and interactions generates narrow and adjustable instability regions, leading to the growth, from quantum or thermal fluctuations, of modes with a density modulation non commensurate with the lattice spacing. This study demonstrates the production of metastable exotic states of matter through Floquet engineering, and paves the way for further studies of dissipation in the resulting phase, and of similar phenomena in other geometries.