Probing number squeezing of ultracold atoms across the superfluid-Mott insulator transition

TL;DR

This paper experimentally investigates how on-site number fluctuations of ultracold atoms evolve across the superfluid-Mott insulator transition, providing direct evidence of number squeezing through suppression of spin-changing collisions.

Contribution

It demonstrates the continuous suppression of spin-changing collisions as a signature of number squeezing and identifies a threshold atom number for Mott plateau formation.

Findings

Suppression of spin-changing collisions indicates number squeezing.

Threshold atom number aligns with Mott plateau formation.

Number fluctuations decrease across the transition.

Abstract

The evolution of on-site number fluctuations of ultracold atoms in optical lattices is experimentally investigated by monitoring the suppression of spin-changing collisions across the superfluid-Mott insulator transition. For low atom numbers, corresponding to an average filling factor close to unity, large on-site number fluctuations are necessary for spin-changing collisions to occur. The continuous suppression of spin-changing collisions is thus a direct evidence for the emergence of number-squeezed states. In the Mott insulator regime, we find that spin-changing collisions are suppressed until a threshold atom number, consistent with the number where a Mott plateau with doubly-occupied sites is expected to form.