Sub-Poissonian atom number fluctuations using light-assisted collisions

TL;DR

This paper demonstrates that light-assisted collisions can significantly reduce atom number fluctuations in a cold atom ensemble, achieving near-ultimate suppression levels in a microscopic trap.

Contribution

The study provides the first experimental evidence of sub-Poissonian atom number fluctuations due to light-assisted collisions in a mesoscopic cold atom system.

Findings

Atom number fluctuations are reduced below Poissonian levels.

Measured Fano factor of 0.72±0.07 for N>2 atoms.

The stochastic model predicts a steady-state Fano factor of 3/4.

Abstract

We investigate experimentally the number statistics of a mesoscopic ensemble of cold atoms in a microscopic dipole trap loaded from a magneto-optical trap, and find that the atom number fluctuations are reduced with respect to a Poisson distribution due to light-assisted two-body collisions. For numbers of atoms N>2, we measure a reduction factor (Fano factor) of 0.72+/-0.07, which differs from 1 by more than 4 standard deviations. We analyze this fact by a general stochastic model describing the competition between the loading of the trap from a reservoir of cold atoms and multi-atom losses, which leads to a master equation. Applied to our experimental regime, this model indicates an asymptotic value of 3/4 for the Fano factor at large N and in steady state. We thus show that we have reached the ultimate level of reduction in number fluctuations in our system.