# How to probe the microscopic onset of irreversibility with ultracold atoms

## TL;DR

This paper proposes experiments with ultracold atoms to observe the microscopic origins of irreversibility, demonstrating probabilistic hysteresis caused by phase space mixing without chaos, and providing a way to experimentally confirm the fundamental mechanisms.

## Contribution

It introduces a novel experimental approach to observe microscopic irreversibility in isolated ultracold atom systems through probabilistic hysteresis and phase space analysis.

## Key findings

- Probabilistic hysteresis observed in ultracold atom experiments.
- Return probability depends on tunable parameters and matches theoretical predictions.
- Mechanism explained without requiring dynamical chaos.

## Abstract

The microscopic onset of irreversibility is finally becoming an experimental subject. Recent experiments on microscopic open and even isolated systems have measured statistical properties associated with entropy production, and hysteresis-like phenomena have been seen in cold atom systems with dissipation (i.e. effectively open systems coupled to macroscopic reservoirs). Here we show how experiments on isolated systems of ultracold atoms can show dramatic irreversibility like cooking an egg. In our proposed experiments, a slow forward-and-back parameter sweep will sometimes fail to return the system close to its initial state. This probabilistic hysteresis is due to the same non-adiabatic spreading and ergodic mixing in phase space that explains macroscopic irreversibility, but realized \textit{without} dynamical chaos; moreover this fundamental mechanism quantitatively determines the probability of return to the initial state as a function of tunable parameters in the proposed experiments. Matching the predicted curve of return probability will be a conclusive experimental demonstration of the microscopic onset of irreversibility.