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Title
Zooming in on Brownian Motion with Einstein’s Speed Demon
Abstract
In 1905, Albert Einstein formulated his seminal model for Brownian motion, the apparently random movement of particles suspended in a fluid. While this theory was a major achievement, it predicted infinite particle velocities at short times! Two years later, Einstein corrected his mistake, predicting a finite “instantaneous velocity”, but stating that the “experiment is impossible.” In this talk, I will describe our work realizing Einstein’s speed demon with an optical tweezer that uses a laser to trap a tiny glass microsphere and can track its motion on nanosecond time scales. We used this device to verify Einstein’s prediction for short-time Brownian motion in equilibrium, both in air and in liquid. Using information, we implemented feedback cooling of the center-of-mass of a microsphere in vacuum and reached a temperature near 1 mK.
We are working on a new generation of experiments that will build on our earlier work to study the onset of viscosity and the arrow of time, requiring a new formulation of the Navier-Stokes equations from an information perspective. Einstein’s speed demon operating in air and in liquid will enable the realization of a quantum limited acoustic detector, with potential impact on the search for dark matter and cancer therapy.
Bio
Mark Raizen’s research is in experimental atomic, molecular, and optical physics. His group pioneered the study of quantum chaos with ultra-cold atoms. In parallel, they studied quantum transport of atoms in accelerating optical lattices, establishing a new paradigm of condensed matter phenomena with ultra-cold atoms. In a recent study of short-time Brownian motion, Mark and his group verified a prediction by Einstein from 1907 and established a new testing ground for fluid dynamics and non-equilibrium dynamics on the microscale. He developed an alternative method for cooling of atoms by realizing a one-way wall which relies on photon entropy, the first practical realization of Maxwell's Demon, proposed by James Clerk Maxwell in 1871. It also changes the way isotopes are separated, with important applications in medicine, now being pursued at a non-profit entity that Mark started, the Pointsman Foundation, www.pointsman.org.
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