Bloch Oscillations of a Soliton in a 1D Quantum Fluid

TL;DR

This paper reports the observation of Bloch oscillations in a mesoscopic solitonic wave packet within a 1D Bose gas, revealing collective quantum behavior without a lattice and highlighting the role of phase coherence and superfluid currents.

Contribution

It demonstrates the first experimental observation of Bloch oscillations of a soliton in a 1D quantum fluid without a lattice, emphasizing collective effects and phase coherence.

Findings

Oscillation period inversely proportional to atom number

Phase coherence crucial for oscillation stability

Reveals periodicity of collective excitation dispersion relation

Abstract

The motion of a quantum system subjected to an external force often defeats our classical intuition. A celebrated example is the dynamics of a single particle in a periodic potential, which undergoes Bloch oscillations under the action of a constant force. Surprisingly, Bloch-like oscillations can also occur in one-dimensional quantum fluids without requiring the presence of a lattice. The intriguing generalization of Bloch oscillations to a weakly-bounded ensemble of interacting particles has been so far limited to the experimental study of the two-particle case, where the observed period is halved compared to the single-particle case. In this work, we observe the oscillations of the position of a mesoscopic solitonic wave packet, consisting of approximately 1000 atoms in a one-dimensional Bose gas when subjected to a constant uniform force and in the absence of a lattice potential. The oscillation period scales inversely with the atom number, thus revealing its collective nature. We demonstrate the pivotal role of the phase coherence of the quantum bath in which the wave packet moves and investigate the underlying topology of the associated superfluid currents. Our measurements highlight the periodicity of the dispersion relation of collective excitations in one-dimensional quantum systems. We anticipate that our observation of such a macroscopic quantum phenomenon will inspire further studies on the crossover between classical and quantum laws of motion, such as exploring the role of dissipation, similarly to the textbook case of macroscopic quantum tunneling in Josephson physics.