Characterizing the Quantum State of Matter Using Emission Tomography
Recent advances in laser technology have stimulated a revival of interest in the study of wave packets in atoms, molecules and in the solid-state. In many experiments, particularly those on atoms and molecules, the aim is to engineer a specific state. Control of the system at the quantum level is intended to initiate a dynamic which can subsequently lead to a desired conclusion; the favoring of a particular dissociation pathway in a molecule, for example, or the generation of states that most closely mimic the dynamics of the equivalent classical system in a Rydberg atom perhaps. In all cases, however, the details of the state prepared by experiment has been inferred from a more or less detailed knowledge of the electric field of the pulse that is used to drive the system. This inference clearly stands or falls on the ability to fully characterize the driving field, but in fact most of the measurements of the nonstationary atomic or molecular states are not sensitive to the full quantum structure of the underlying wave packet, so that a lack of knowledge of the driving pulse is offset by a relatively coarse measurement of the state of the matter system. This is a particularly pressing problem for experiments in which data is acquired over an ensemble of pulses, since then it is impossible to calculate the density matrix unless the statistical properties of the generating pulse ensemble is known. Techniques for complete characterization of a partially-coherent ensemble of optical pulses have only recently been developed.
KeywordsWave Packet Wigner Function Excited Electronic State Observation Window Time Gate
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