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Updated: Feb 15, 2026

Construction and Characterization of External Cavity Diode Lasers for Atomic Physics
Published on: April 24, 2014
Negative-Mass Instability of the Spin and Motion of an Atomic Gas Driven by Optical Cavity Backaction
Jonathan Kohler1, Justin A Gerber1, Emma Dowd1
1Department of Physics, University of California, Berkeley, California 94720, USA.
Abstract:
We realize a spin-orbit interaction between the collective spin precession and center-of-mass motion of a trapped ultracold atomic gas, mediated by spin- and position-dependent dispersive coupling to a driven optical cavity. The collective spin, precessing near its highest-energy state in an applied magnetic field, can be approximated as a negative-mass harmonic oscillator. When the Larmor precession and mechanical motion are nearly resonant, cavity mediated coupling leads to a negative-mass instability, driving exponential growth of a correlated mode of the hybrid system. We observe this growth imprinted on modulations of the cavity field and estimate the full covariance of the resulting two-mode state by observing its transient decay during subsequent free evolution.
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