# Light-Mediated Collective Atomic Motion in an Optical Lattice Coupled to a Membrane

## TL;DR

This paper demonstrates how collective atomic motion in an optical lattice coupled to a membrane can lead to optomechanical instabilities, with experimental observations aligning with theoretical predictions of light-mediated interactions.

## Contribution

It provides the first experimental evidence of light-mediated collective atomic motion causing instabilities in a hybrid atom-optomechanical system.

## Key findings

- Large atom numbers induce system instability.
- Instability results in large-amplitude atom-membrane oscillations.
- The behavior aligns with theoretical models of light-mediated atomic interactions.

## Abstract

We observe effects of collective atomic motion in a one-dimensional optical lattice coupled to an optomechanical system. In this hybrid atom-optomechanical system, the lattice light generates a coupling between the lattice atoms as well as between atoms and a micromechanical membrane oscillator. For large atom numbers we observe an instability in the coupled system, resulting in large-amplitude atom-membrane oscillations. We show that this behavior can be explained by light-mediated collective atomic motion in the lattice, which arises for large atom number, small atom-light detuning and asymmetric pumping of the lattice, in agreement with previous theoretical work. The model connects the optomechanical instability to a phase delay in the global atomic back-action onto the lattice light, which we observe in a direct measurement.