Disappearance of Quasiparticles in a Bose Lattice Gas

TL;DR

This paper investigates how quasiparticles disappear in a Bose lattice gas by measuring momentum relaxation times using a novel hole-burning technique, revealing a crossover that challenges traditional quasi-particle models.

Contribution

It introduces a momentum-space hole-burning method for measuring relaxation times and demonstrates a crossover indicating quasiparticle breakdown in a Bose lattice gas.

Findings

Relaxation times vary with lattice depth, crossing the bandwidth.

Breakdown of the quasi-particle picture occurs when relaxation time is less than the bandwidth.

A kinetic model accurately predicts the observed relaxation times.

Abstract

We use a momentum-space hole-burning technique implemented via stimulated Raman transitions to measure the momentum relaxation time for a gas of bosonic atoms trapped in an optical lattice. By changing the lattice potential depth, we observe a smooth crossover between relaxation times larger and smaller than the bandwidth. The latter condition violates the Mott-Ioffe-Regal bound and indicates a breakdown of the quasi-particle picture. We produce a simple kinetic model that quantitatively predicts these relaxation times. Finally, we introduce a cooling technique based upon our hole-burning technique.