Optically detecting the quantization of collective atomic motion

TL;DR

This paper demonstrates direct optical measurement of quantized collective atomic motion in a large ultracold gas, revealing asymmetries in motional sidebands and quantifying measurement backaction effects.

Contribution

It introduces a method to detect and analyze quantized collective motion of ultracold atoms via optical cavity measurements, highlighting backaction effects on phonon occupation.

Findings

Asymmetry in motional sidebands up to 3:1 ratio observed.

Optical cavity output records energy exchange between light and motion.

Measurement backaction increases phonon occupation of collective modes.

Abstract

We directly measure the quantized collective motion of a gas of thousands of ultracold atoms, coupled to light in a high-finesse optical cavity. We detect strong asymmetries, as high as 3:1, in the intensity of light scattered into low- and high-energy motional sidebands. Owing to high cavity-atom cooperativity, the optical output of the cavity contains a spectroscopic record of the energy exchanged between light and motion, directly quantifying the heat deposited by a quantum position measurement's backaction. Such backaction selectively causes the phonon occupation of the observed collective modes to increase with the measurement rate. These results, in addition to providing a method for calibrating the motion of low-occupation mechanical systems, offer new possibilities for investigating collective modes of degenerate gases and for diagnosing optomechanical measurement backaction.