Brownian motions under direct observation

Here is surely a very interesting report, which shall reveal a lot of details about the motions under noices. In my opinion, although many have been learned of such motions, they remain mysterious in short-time scale dynamics. Further, what about a quantum particle in noices.

Science 25 June 2010:
Vol. 328. no. 5986, pp. 1673 - 1675
DOI: 10.1126/science.1189403

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Reports
Measurement of the Instantaneous Velocity of a Brownian Particle
Tongcang Li, Simon Kheifets, David Medellin, Mark G. Raizen*

Brownian motion of particles affects many branches of science. We report on the Brownian motion of micrometer-sized beads of glass held in air by an optical tweezer, over a wide range of pressures, and we measured the instantaneous velocity of a Brownian particle. Our results provide direct verification of the energy equipartition theorem for a Brownian particle. For short times, the ballistic regime of Brownian motion was observed, in contrast to the usual diffusive regime. We discuss the applications of these methods toward cooling the center-of-mass motion of a bead in vacuum to the quantum ground motional state.

Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, TX 78712, USA.

* To whom correspondence should be addressed. E-mail: raizen@physics.utexas.edu