Continuous observation of quantum dynamics

Citation

Mabuchi, Hideo (1998) Continuous observation of quantum dynamics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/sgc8-n788. https://resolver.caltech.edu/CaltechETD:etd-03172006-093206

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Previous work in cavity quantum electrodynamics has focused principally on achieving the condition of strong coupling, such that the single-photon Rabi frequency for one atom in a cavity dominates the rates associated with all forms of dissipation and dephasing. Although strong coupling was convincingly demonstrated in these experiments, the use of thermal atomic beams as a source of atoms invariably limited the intracavity dwell time of any given atom to values marginally longer than the system's characteristic dynamical timescales. Accordingly, the observation of single-atom effects in these experiments required integration over the transits of many successive atoms through the optical resonator. In such ensemble-averaged experiments, the quantitative effects of dissipation and measurement could always be understood from the perspective of Master Equation formalisms. By contrast, our most recent work has incorporated laser cooling techniques to accomplish a thousand-fold increase in the dwell time of individual atoms while maintaining conditions of strong coupling. With this extreme separation of timescales, the effects of individual atoms on the cavity transmission can clearly be resolved. Moreover, detailed information on each individual atom's spatial trajectory through the cavity can be inferred from the time-varying amplitude and phase of the transmitted light. Understanding the exact nature of such correlations in real laboratory measurements requires not only a careful characterization of excess technical noise, but also an in-depth study of how (and when) aspects of continuous quantum measurement theory should properly be applied. This thesis primarily contains a detailed description of an experiment in which we used broadband heterodyne spectroscopy to record the complete time-evolution of interaction energy between one atom and a high-finesse optical cavity, during individual scattering events of [...] duration. With a characteristic interaction energy scale [...], we achieve a shot-noise limited measurement sensitivity [...] over a bandwidth that covers the dominant rates of variation in [...]. I also include two brief studies in quantum measurement theory, which highlight the significance of the experimental work for continuing research on conditional quantum dynamics. The first investigates quantum limits to broadband measurement of position and force, and the second proposes a novel trajectory-based approach to quantum system identification.

Thesis Files