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Reconsidering weak values


In 1988 Yakir Aharonov, David Albert, and Lev Vaidman wrote a paper provocatively titled "How the result of a measurement of a component of the spin of a spin-1/2 particle can turn out to be 100". In this paper they defined a quantity, similar to the expectation value of an operator, called the "weak value" of an operator. The weak value of an operator has many weird properties which has lead some researchers to: (1) think that quantum paradoxes are solved by this defined quantity, and (2) suggest that the weak value can be used to perform sensitive measurements. In this talk I will address both points. First, I argue that the phenomenon of anomalous weak values is not limited to quantum theory. In particular, I show that the same features occur in a simple model of a coin subject to a form of classical backaction with pre- and post-selection. Second, I will explain how rigorous estimation and detection theory imply that weak values do not aid quantum metrology. This is joint work with Chris Ferrie of the University of New Mexico.