Quantum Micro-Mechanics with Ultracold Atoms

Kater Murch
Department of Physics, UC Berkeley

A common goal of recent research is the elucidation and control over quantum mechanical behaviour in ever-larger physical systems. We present an alternative target for investigating the quantum motion of macroscopic bodies: the collective motion of an ultracold atomic gas trapped within a high-finesse Fabry-Perot optical cavity in the single-atom strong-coupling regime of cavity quantum electrodynamics (CQED). When the ultracold atoms are trapped in the Lamb-Dicke regime, the cavity-mode structure selects a single collective degree of freedom that is at once actuated by the optical forces from cavity probe light and measured by the cavity's optical properties. For this, an optically trapped, ultracold Rubidium gas in probed dispersively in a high-finesse cavity allowing observation of dispersive optical-bistability arising from collective motion of the atomic medium. Measurement of the collective motion is subject to quantum-measurement backaction by the quantum force fluctuations of the cavity optical field. Experimentally, we measure the strength and spectrum of these back-action force fluctuations by quantifying the cavity-light-induced heating rate of the intracavity atomic ensemble, finding quantitative agreement with the expected heating rate from quantum optical fluctuations.