Quantum Optics Seminar by Mark G. Raizen – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Mark G. Raizen

                             In this talk I will review our recent experiments on trapping of glass microspheres in liquid, gas, and vacuum.  This work was motivated, in part, by a 1907 paper by Albert Einstein  where he considered Brownian motion on short time scales.  He predicted that there should be a regime of ballistic motion, unlike random diffusion at longer times.  Einstein concluded that this "instantaneous velocity"  would be impossible to measure in practice, a prediction that held true for over 100 years.  Using the ultra-high sensitivity of our system, we have now measured the instantaneous velocity of a Brownian particle in a gas and in liquids [1,2].   This work opens the door to the study of statistical mechanics of small systems, non-equilibrium dynamics, and the onset of the "arrow of time."

                             An optically trapped particle in vacuum is an ideal system for investigating quantum effects in a mechanical system, due to its near-perfect isolation from the thermal environment.  We have implemented feedback cooling to control the motion of a trapped microsphere in vacuum. We are able to reduce the center-of-mass temperature of the bead from 300K to 2 mK with this method [3]. We are investigating optimal approaches toward cooling of the bead to the quantum ground state, and the preparation of superposition states of the bead.


[1]  T. Li, S. Kheifets, D. Medellin, and M. G. Raizen, Science 328, 1673 (2010).

[2] S. Kheifets, A. Simha, K. Melin, T. Li, and M. G. Raizen, Science 343, 6178 (2014).

[3]  T. Li, S. Kheifets, and M. G. Raizen, Nature Physics 7, 527 (2011).