Abstract

Throughout the 20th century, the question of quantum measurement has confused and intrigued physicists. At the dawn of the 21st, these issues have taken on new practical importance due to the birth of the interdisciplinary science of "quantum information." The realization that quantum mechanics allows communications more secure than one could ever have classically, and computation exponentially more efficient than any known classical algorithms, has incited a huge amount of research into this new area, which has in turn provided an exciting new perspective on quantum mechanics. Motivated in part by these considerations, my lab has been carrying out a variety of experiments on controlling simple quantum systems and comparing different techniques for "measuring" their wave functions, density matrices, or phase-space distributions. I will describe some of the current issues in measurement and characterisation of quantum systems, and show the results of some of our recent experiments, including the generation of multi-photon entangled states for "super-resolution" and the optimisation of pulse sequences for control of coherence in optical lattices. In addition, if time permits, I may discuss our work on "weak measurements," a paradigm which makes it possible to describe the state of a quantum system before a post-selection event. Such measurements illuminate a number of quantum "mysteries," and may also be the only appropriate way to deal with the sorts of post-selected systems which are central to many quantum information protocols.



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