Research done by the Chiao Group


Over the past few years we have performed experiments on two-photon interference. These included a test of Bell's inequalities, a study of the complementarity principle, an application of EPR correlations for dispersion-free time-measurements, and an experiment to demonstrate the superluminal nature of the tunneling process. The nonlocal character of the quantum world was brought out clearly by these experiments. However, we have shown that quantum nonlocality is not inconsistent with Einstein causality.

Today we are investigating population inversions in atomic or molecular media. This has led us to the possibility of superluminal propagation of off-resonance, finite-bandwidth electromagnetic wave packets, whose phase, group, energy, and ``signal'' velocities, as defined by Sommerfeld and Brillouin, all exceed the vacuum speed of light c. Einstein causality is not violated, since the front velocity is c. We are proposing an experiment to observe superluminal propagation of laser pulses detuned from a stimulated Raman transition in optically pumped rubidium vapor. The inversion of populations also can lead to a parelectric medium with negative DC electric susceptibility, thus implying the possibility of the levitation of an electrical charge in the vacuum above this medium. Stable electrostatic configurations of charges placed inside an evacuated cavity surrounded by this medium exist, in seeming violation of Earnshaw's theorem.

Simulation of superluminal pulse propagation.
(This movie works best if saved as a QuickTime at 12 frames/sec.)


Experimental setup to observe superluminal pulse propagation.

Recent Publications:

For more information write to:

Professor Raymond Y. Chiao

Mailing Address:
Department of Physics
366 LeConte Hall
University of California at Berkeley
Berkeley, CA 94720