Quantum Capillary Waves at the Superfluid--Mott Insulator Interface

TL;DR

This paper explores quantum fluctuations at the interface between superfluid and Mott-insulating states in ultracold atoms, revealing a new type of surface mode similar to capillary waves that influence interface properties.

Contribution

It introduces a novel quantum surface mode spectrum at the superfluid-Mott insulator boundary and quantifies the quantum capillary length affecting interface penetration and width.

Findings

Quantum surface modes analogous to capillary waves are identified.

The quantum capillary length can be several lattice spacings.

Interface width due to quantum fluctuations can be measured via single site imaging.

Abstract

We discuss quantum fluctuations of the interface between a superfluid and a Mott-insulating state of ultracold atoms in a trap. The fluctuations of the boundary are due to a new type of surface modes, whose spectrum is similar (but not identical) to classical capillary waves. The corresponding quantum capillary length sets the scale for the penetration of the superfluid into the Mott-insulating regime by the proximity effect and may be on the order of several lattice spacings. It determines the typical magnitude of the interface width due to quantum fluctuations, which may be inferred from single site imaging of ultracold atoms in an optical lattice.