# Observation of Dynamical Fermionization

## TL;DR

This paper reports the experimental observation of dynamical fermionization in a 1D strongly interacting bosonic gas, showing the evolution of momentum distribution from bosonic to fermionic and measuring rapidities, a novel achievement.

## Contribution

First measurement of rapidities in an interacting many-body quantum system, confirming theoretical predictions of dynamical fermionization in a 1D Bose gas.

## Key findings

- Momentum distribution evolves from bosonic to fermionic after trap removal.
- Measured rapidities match theoretical predictions for T-G gases.
- Observed bosonic-fermionic oscillations after changing trap depth.

## Abstract

We observe dynamical fermionization, where the momentum distribution of a Tonks-Girardeau (T-G) gas of strongly interacting bosons in 1D evolves from bosonic to fermionic after its axial confinement is removed. The asymptotic momentum distribution after expansion in 1D is the distribution of rapidities, which are the conserved quantities associated with many-body integrable systems. Rapidities have not previously been measured in any interacting many-body quantum system. Our measurements agree well with T-G gas theory. We also study momentum evolution after the trap depth is suddenly changed to a new non-zero value. We observe the predicted bosonic-fermionic oscillations and see deviations from the theory outside of the T-G gas limit.