TITLE: "Quantum Feedback in Cavity QED" or the "Capture and Release of a Quantum Butterfly"

SPEAKER: Professor Luis A. Orozco,

TIME: Thursday Apr. 10, 2003 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

Quantum states are easily disturbed, like a butterfly on a twig. Just looking at a quantum system can change its state dramatically, and the new state may "flutter" (oscillate) as the system settles down again. In the first quantum feedback experiment to investigate this, we have shown that the post-measurement state can be precisely controlled. By shining a carefully timed light pulse on a Cavity QED (Quantum Electro-Dynamical) system, we freeze the quantum state, stopping the oscillations for an arbitra ry time. When this feedback pulse is turned off, the oscillations return, with identical amplitude and phase. The detection of a single photon causes the state-change, or quantum jump, and starts the oscillations, and this single bit of information triggers the feedback. The capture and release of the quantum state, the "quantum butterfly", opens avenues for many studies in the manipulation of quantum states for quantum information, quantum computing and quantum optics.