# Remote Hamiltonian Interactions Mediated by Light

## TL;DR

This paper demonstrates that light can mediate coherent Hamiltonian interactions between distant quantum systems, even with optical losses, by satisfying a specific interaction condition involving time-reversal, enabling entanglement and hybrid quantum system applications.

## Contribution

It provides a simple sufficient condition for light-mediated Hamiltonian interactions, showing they can be realized despite losses and enabling new quantum system architectures.

## Key findings

- Coherent interactions are possible with light interacting twice and time-reversal.
- Significant entanglement can be generated despite optical losses.
- Method applicable to optomechanics and atomic ensembles.

## Abstract

We address a fundamental question of quantum optics: Can a beam of light mediate coherent Hamiltonian interactions between two distant quantum systems? This is an intriguing question whose answer is not a priori clear, since the light carries away information about the systems and might be subject to losses, giving rise to intrinsic decoherence channels associated with the coupling. Our answer is affirmative and we derive a particularly simple sufficient condition for the interactions to be Hamiltonian: The light field needs to interact twice with the systems and the second interaction has to be the time reversal of the first. We demonstrate that, even in the presence of significant optical loss, coherent interactions can be realized and generate substantial amounts of entanglement between the systems. Our method is directly applicable for building hybrid quantum systems, with relevant applications in the fields of optomechanics and atomic ensembles.