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Light shifts of ground-state quantum beats: A consequence of quantum jumps.

Luis Orozco, Joint Quantum Institute, Dept. Physics and National Institute of Standards and Technology, University of Maryland

(Session 7 : Saturday from 9:15am-9:45am)

Abstract.

Spontaneous emission in resonance fluorescence is a fundamental process in which an atom loses energy and the dipole emission of radiation is interrupted, with the consequence of damping. This process has been studied under different conditions, and the analysis with two-level atoms has given many insights into the behavior of more complicated atomic structure. The multi-level atom often has ground-state hyperfine and Zeeman structure. This structure allows the manipulation of ultra-cold atoms in areas as different as atomic clocks and quantum information processing. We present a study of ground-state light shifts with weak coherent excitation when the light is quasi-resonant with an electronic excited state of⁸⁵Rb (within a linewidth). This mechanism is only discernible through the polarization mode selection (drive V, measure H) available in cavity QED and the powerful signals coming from ground-state quantum beats, and correlation measurements on the H mode. The shift requires the presence of spontaneous emission, which generally preserves the ground-state coherence but induces a significant frequency shift with the presence of even a single photon.

Quantum trajectories show that quantum jumps on the driven V mode (pi transitions) that happen in between H detections cause phase shifts on the Larmor precesion. Quantum jumps interrupt the atomic dipole and transfer the differential phase accumulated by the excited state to the ground state. The stochastic process of the quantum jumps produces both a frequency shift, if the phase jumps are small compared to p, and a broadening of the spectral linewidth from the phase diffusion process.

Work performed by David G. Morris, Adres D. Cimmarusti, Luis A. Orozco, Pablo Barberis-Blostein and H. J Carmichael with support from NSF, USA; CONACYT, Mexico; and The Marsden Fund of the Royal Society of New Zealand.