Transition from a strongly interacting 1D superfluid to a Mott insulator

TL;DR

This paper investigates the transition of one-dimensional Bose gases from a superfluid to a Mott insulator using Bragg spectroscopy, revealing distinct excitation spectra and increased fluctuations characteristic of 1D quantum systems.

Contribution

It provides experimental characterization of excitation spectra and coherence properties during the superfluid to Mott insulator transition in 1D Bose gases, including effects beyond mean-field theory.

Findings

Broad excitation continuum in superfluid phase

Discrete spectrum in Mott insulator phase

Signatures of increased quantum fluctuations

Abstract

We study one-dimensional trapped Bose gases in the strongly interacting regime. The systems are created in an optical lattice and are subject to a longitudinal periodic potential. Bragg spectroscopy enables us to investigate the excitation spectrum of the one-dimensional gas in different regimes. In the superfluid phase a broad continuum of excitations is observed which calls for an interpretation beyond the Bogoliubov spectrum taking into account the effect of quantum depletion. In the Mott insulating phase a discrete spectrum is measured. The excitation spectra of both phases are compared to the three-dimensional situation and to the crossover regime from one to three dimensions. The coherence length and coherent fraction of the gas in all configurations are measured quantitatively. We observe signatures for increased fluctuations which are characteristic for 1D systems. Furthermore, ceasing collective oscillations near the transition to the Mott insulator phase are found.