Colloquium: Dr. David Mason, Yale University

Mechanical oscillators have long been a model system for understanding quantum principles like measurement and decoherence.  Recent technological progress has made these ideas accessible in the laboratory, enabling both tests of fundamental physics and precision sensing applications.  Here, I'll present work using optical interferometry to make displacement measurements that operate near fundamental quantum limits.  By making a strong, efficient measurement, we probe our resonator nearly as fast as it decoheres, reaching within 35% of the Heisenberg imprecision-backaction limit.  This strong, efficient measurement actually projects the mechanical system into a conditional coherent state of high purity. By using a retrodiction protocol, we verify this purity, and even directly visualize the measurement-induced collapse of our mechanical state. Our ability to apply the tools of quantum optics to mechanical systems is an indicator of their broad potential in emerging quantum technologies.

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