RECORDING LONG-TERM OPTICAL-IMAGES OF A BROWNIAN PARTICLE IN A PAUL TRAP ESSENTIALLY FREE OF THERMALLY-INDUCED POSITIONAL NOISE

We show experimentally that the positional uncertainty in long-term im ages of a microparticle in a Paul trap in air can be reduced to the op tical limit, and below the pseudopotential limit. For this damped syst em, far below any Mathieu instability, the particle's thermally induce d positional noise is extremely sensitive to the phase of the driving field. Accumulating images strobed at the proper phase produces a long -term optical image which is essentially free of thermally induced pos itional noise. Although noise squeezing theory does not apply at such large dissipation, our results may be understood through recent theory of the Brownian parametric oscillator, Use of this theory coupled wit h our observations suggests that the extreme reduction in spatial vari ance observed by using our technique results from working in a low Rey nolds number regime. (C) 1995 American Institute of Physics.