Observation of quantum-measurement backaction with an ultracold atomic gas

TL;DR: In this paper, the collective motion of an ultracold atomic gas confined tightly within a Fabry-Perot optical cavity was established as a system for investigating the quantum mechanics of macroscopic bodies.

Abstract: Current research on micromechanical resonators strives for quantum-limited detection of the motion of macroscopic objects. Prerequisite to this goal is the observation of measurement backaction consistent with quantum metrology limits. However, thermal noise currently dominates measurements and precludes ground-state preparation of the resonator. Here, we establish the collective motion of an ultracold atomic gas confined tightly within a Fabry–Perot optical cavity as a system for investigating the quantum mechanics of macroscopic bodies. The cavity-mode structure selects a particular collective vibrational motion that is measured by the cavity’s optical properties, actuated by the cavity optical field and subject to backaction by the quantum force fluctuations of this field. Experimentally, we quantify such fluctuations by measuring the cavity-light-induced heating of the intracavity atomic ensemble. These measurements represent the first observation of backaction on a macroscopic mechanical resonator at the standard quantum limit. Nanoscale beams are one platform for exploring quantum-mechanical phenomena in ever-larger systems. The collective motion of a macroscopic ensemble of ultracold atoms confined in an optical cavity is established as an alternative approach.