Quantum limits to precision measurement of an object’s displacement, and correspondingly the forces acting on the object, have been well studied since the 1970’s . In the case of laser interferometers, such as those developed to detect gravitational waves, quantum fluctuations of the probe laser field set the level of imprecision for displacement sensitivity and also give rise to quantum back-action on the mechanical object being measured via radiation pressure shot noise. This part of the story, as well as back-action evading or quantum nondemolition measurement schemes, has been covered extensively, theoretically. Recent experiments with much smaller chip-scale devices have for the first time measured the effects of quantum back-action in the context of cavity-optomechanics [2-4]. I will describe two of these experiments that have been performed at Caltech. The first involves measurement of the relative amplitude of the Stokes and anti-Stokes motional sidebands created on a probe laser field by a mechanical resonator near its quantum ground-state of motion. An asymmetry in the generated motional sidebands, as has been utilized in experiments with trapped ions and atoms, provides a self-calibrated means of measuring the mechanical oscillator’s quantum occupancy. An alternative view of such experiments , one from the perspective of continuous position measurement of the mechanical oscillator, provides an interesting twist in interpreting the source of the measured sideband asymmetry. A second experiment, involves the use of strong measurement by a probe laser field to generate, via quantum back-action, squeezed light from a silicon micromechanical resonator.
 Carlton M. Caves, Kip S. Thorne, Ronald W. P. Drever t Vernon D. Sandberg, and Mark Zimmermann, “On the measurement of a weak classical force coupled to a quantum-mechanical oscillator. I. Issues of principle,” Rev. Mod. Phys. 52, 341 (1980).
 Amir H. Safavi-Naeini, Jasper Chan, Jeff T. Hill, T. P. Mayer Alegre, Alex Krause, and Oskar Painter, "Observation of quantum motion of a nanomechanical resonator," Phys. Rev. Lett., art. 033602, (Jan. 17 2012).
¿3¿ Daniel W. C. Brooks, Thierry Botter, Sydney Schreppler, Thomas P. Purdy, Nathan Brahms, and Dan M. Stamper-Kurn, “Non-classical light generated by quantum-noise-driven cavity optomechanics,” Nature 488, 476–480 (23 August 2012).
 T. P. Purdy, R. W. Peterson, and C. A. Regal, “Observation of Radiation Pressure Shot Noise,” arXiv:1209.6334 (September 27, 2012).
 Farid Ya. Khalili, Haixing Miao, Huan Yang, Amir H. Safavi-Naeini, Oskar Painter, and Yanbei Chen, "Quantum back-action in measurements of zero-point mechanical oscillations," PHYSICAL REVIEW A, v86, art. 033840, (September 25, 2012).
Oskar Painter received his B.S.E.E. from the University of British Columbia in 1994, his Masters Degree of Science from the California Institute of Technology in 1995, and his Ph.D. in Electrical Engineering from the California Institute of Technology in 2001. In 2000 he helped found Xponent Photonics, an optical start-up company developing surface-mount photonics for telecom and data networking applications. In 2002 he returned to the California Institute of Technology, where he is currently a Professor of Applied Physics.
Dr. Painter's general research interests lie in studying new and interesting ways in which light behaves within micro- and nano-scale structures. Areas of current research include the study of cavity-optomechanical systems in the quantum regime and development of nanophotonic structures for quantum atom-photon systems.