What is a quantum shock wave?

TL;DR

This paper investigates the microscopic quantum mechanisms behind shock wave formation in a one-dimensional Bose gas, revealing that quantum interference and fluctuations significantly influence shock wave dynamics and visibility.

Contribution

It demonstrates that quantum self-interference causes oscillatory shock waves and analyzes how temperature, interactions, and fluctuations affect their coherence.

Findings

Quantum interference causes oscillatory shock waves.

Temperature and interactions reduce interference contrast.

Fluctuations wash out interference fringes.

Abstract

Shock waves are examples of the far-from-equilibrium behaviour of matter; they are ubiquitous in nature, yet the underlying microscopic mechanisms behind their formation are not well understood. Here, we study the dynamics of dispersive quantum shock waves in a one-dimensional Bose gas, and show that the oscillatory train forming from a local density bump expanding into a uniform background is a result of quantum mechanical self-interference. The amplitude of oscillations, i.e., the interference contrast, decreases with the increase of both the temperature of the gas and the interaction strength due to the reduced phase coherence length. Furthermore, we show that vacuum and thermal fluctuations can significantly wash out the interference contrast, seen in the mean-field approaches, due to shot-to-shot fluctuations in the position of interference fringes around the mean.