Observing dissipationless flow of an impurity in a strongly repulsive quantum fluid

TL;DR

This paper demonstrates that a microscopic impurity can move through a strongly interacting 1D Bose gas without friction, challenging traditional views on superfluidity and dissipation in quantum fluids.

Contribution

It provides experimental evidence of dissipationless impurity motion in a 1D quantum fluid, showing quantum effects can suppress friction contrary to Landau's criteria.

Findings

Impurity propagates without friction in a strongly interacting 1D Bose gas.

Shock waves form at supersonic initial velocities.

Impurity reaches a stationary velocity, indicating dissipationless flow.

Abstract

The frictionless motion of an object through a fluid medium is commonly viewed as a hallmark of superfluidity. According to Landau, kinematic constraints prohibit superfluid behavior in one-dimensional (1D) bosonic systems. Here, using ultracold atoms, we show how a microscopic impurity can propagate through a strongly interacting 1D Bose gas without any friction, at odds with conventional expectations. We inject the impurity with initial velocities ranging from the subsonic to supersonic regime, and subsequently track its dynamics. For supersonic initial velocities, we observe the formation of a shock wave and a remarkably fast relaxation to a stationary regime, on a time scale that increases with decreasing impurity velocity. After reaching the stationary state, the impurity continues its motion through the system with a finite velocity. Our findings demonstrate how quantum effects can conspire to eliminate dissipation of a microscopic object immersed in a quantum fluid, thereby bringing novel insights into the propagation of matter and information in the quantum realm.