# Formation of a sonic horizon in isotropically expanding Bose-Einstein condensates

## TL;DR

This paper proposes a feasible experiment to generate a sonic horizon in expanding Bose-Einstein condensates, enabling the study of analog Hawking radiation with current technology.

## Contribution

It introduces a simple method to create a sonic horizon in cold atom systems via controlled expansion and interaction tuning, supported by numerical simulations.

## Key findings

- Sonic horizon forms during condensate expansion
- Horizon remains quasi-static under certain conditions
- Estimated Hawking temperature is a few nanokelvin

## Abstract

We propose a simple experiment to create a sonic horizon in isotropically trapped cold atoms within currently available experimental techniques. Numerical simulation of the Gross-Pitaevskii equation shows that the sonic horizon should appear by making the condensate expand. The expansion is triggered by changing the interaction which can be controlled by the Feshbach resonance in real experiments. The sonic horizon is shown to be quasi-static for sufficiently strong interaction or large number of atoms. The characteristic temperature that is associated with particle emission from the horizon, which corresponds to the Hawking temperature in an ideal situation, is estimated to be a few nK.