Amplification of Fluctuations in a Spinor Bose Einstein Condensate

TL;DR

This paper demonstrates a tunable quantum spin amplifier using a spinor Bose-Einstein condensate, revealing nearly quantum-limited amplification of microscopic spin fluctuations with high gain.

Contribution

It introduces a new method to amplify and measure quantum spin fluctuations in a spinor BEC, aligning experimental results with beyond-mean-field theories.

Findings

Amplifier spectrum is tunable and matches mean-field calculations.

Microscopic spin fluctuations are quantified and agree with theoretical predictions.

Achieved nearly quantum-limited amplification with a gain of up to 30 dB.

Abstract

Dynamical instabilities due to spin-mixing collisions in a $^{87}$Rb F=1 spinor Bose-Einstein condensate are used as an amplifier of quantum spin fluctuations. We demonstrate the spectrum of this amplifier to be tunable, in quantitative agreement with mean-field calculations. We quantify the microscopic spin fluctuations of the initially paramagnetic condensate by applying this amplifier and measuring the resulting macroscopic magnetization. The magnitude of these fluctuations is consistent with predictions of a beyond-mean-field theory. The spinor-condensate-based spin amplifier is thus shown to be nearly quantum-limited at a gain as high as 30 dB.