Enhanced and reduced atom number fluctuations in a BEC splitter

TL;DR

This paper investigates atom number fluctuations in a Bose-Einstein condensate split in a magnetic double-well, revealing quantum statistical effects that lead to both reduced and increased fluctuations depending on temperature.

Contribution

The study provides experimental evidence of super-shot noise fluctuations in a BEC splitter and confirms their quantum origin through simulations.

Findings

Reduced fluctuations of -4.9dB below shot noise at low temperatures

Fluctuations increase to +3.8dB near the critical temperature

Fluctuations return to shot noise level at higher temperatures

Abstract

We measure atom number statistics after splitting a gas of ultracold 87Rb atoms in a purely magnetic double-well potential created on an atom chip. Well below the critical temperature for Bose-Einstein condensation T_c, we observe reduced fluctuations down to -4.9dB below the atom shot noise level. Fluctuations rise to more than +3.8dB close to T_c, before reaching the shot noise level for higher temperatures. We use two-mode and classical field simulations to model these results. This allows us to confirm that the super-shot noise fluctuations directly originate from quantum statistics.