# Universal Dynamics of a Degenerate Bose Gas Quenched to Unitarity

## TL;DR

This paper investigates the universal dynamics of a degenerate Bose gas quenched to unitarity, revealing exponential momentum distribution behavior that is independent of interaction details, consistent with experimental observations.

## Contribution

The study connects two-body and many-body dynamics, demonstrating universal exponential behavior in the momentum distribution after a quench to unitarity.

## Key findings

- Long-time momentum distribution exhibits universal exponential decay.
- The exponential behavior is linked to a sub-leading term in the initial wave function.
- Results are consistent with experimental observations from Cambridge.

## Abstract

Motivated by an unexpected experimental observation from the Cambridge group, [Eigen {\it et al.,} Nature {\bf563}, 221 (2018)], we study the evolution of the momentum distribution of a degenerate Bose gas quenched from the weakly interacting to the unitarity regime. For the two-body problem, we establish a relation that connects the momentum distribution at a long time to a sub-leading term in the initial wave function. For the many-body problem, we employ the time-dependent Bogoliubov variational wave function and find that, in certain momentum regimes, the momentum distribution at long times displays the same exponential behavior found by the experiment. Moreover, we find that this behavior is universal and independent of the short-range details of the interaction potential. Consistent with the relation found in the two-body problem, we also numerically show that this exponential form is hidden in the same sub-leading term of the Bogoliubov wave function in the initial stages. Our results establish a consistent picture to understand the universal dynamics observed in the Cambridge experiment.