A Primary Noise Thermometer for Ultracold Bose Gases

TL;DR

This paper demonstrates a novel primary thermometer based on phase fluctuations in a bosonic Josephson junction, enabling temperature measurements of ultracold Bose gases far below the critical temperature where traditional methods are ineffective.

Contribution

It introduces a new thermometry technique using phase fluctuations in a weakly coupled Bose-Einstein condensate system, validated by experimental and theoretical agreement.

Findings

Phase fluctuations accurately measure ultra-low temperatures.

The method extends thermometry below the critical temperature.

Heat capacity of Bose gases was experimentally probed.

Abstract

We discuss in detail the experimental investigation of thermally induced fluctuations of the relative phase between two weakly coupled Bose-Einstein condensates. In analogy to superconducting Josephson junctions, the weak coupling originates from a tunneling process through a potential barrier which is obtained by trapping the condensates in an optical double-well potential. The observed fluctuations of the relative phase are in quantitative agreement with a many body two mode model at finite temperature. The agreement demonstrates the possibility of using the phase fluctuation measurements in a bosonic Josephson junction as a primary thermometer. This new method allows for measuring temperatures far below the critical temperature where standard methods based on time of flight measurements fail. We employ this new thermometer to probe the heat capacity of a degenerate Bose gas as a function of temperature.