Maximum Energy Growth Rate in Dilute Quantum Gases

TL;DR

This paper investigates the maximum rate at which the energy density of a dilute quantum gas can increase when the inter-atomic interaction is varied over time, revealing a universal maximum growth rate achieved by a specific time dependence of the scattering length.

Contribution

The study derives the universal maximum energy growth rate in dilute quantum gases during time-dependent interaction tuning, supported by analytical and numerical methods.

Findings

Maximum energy growth rate scales as √t at short times.

Universal maximum growth rate occurs when scattering length varies as √t.

Faster or slower variation results in slower energy growth.

Abstract

In this letter we study how fast the energy density of a quantum gas can increase in time, when the inter-atomic interaction characterized by the $s$-wave scattering length $a_\text{s}$ is increased from zero with arbitrary time dependence. We show that, at short time, the energy density can at most increase as $\sqrt{t}$, which can be achieved when the time dependence of $a_\text{s}$ is also proportional to $\sqrt{t}$, and especially, a universal maximum energy growth rate can be reached when $a_\text{s}$ varies as $2\sqrt{\hbar t/(\pi m)}$. If $a_\text{s}$ varies faster or slower than $\sqrt{t}$, it is respectively proximate to the quench process and the adiabatic process, and both result in a slower energy growth rate. These results are obtained by analyzing the short time dynamics of the short-range behavior of the many-body wave function characterized by the contact, and are also confirmed by numerical solving an example of interacting bosons with time-dependent Bogoliubov theory. These results can also be verified experimentally in ultracold atomic gases.