Quantum Optics Seminar by Lev Vaidman – University of Copenhagen

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Quantum Optics Seminar by Lev Vaidman

Past of a quantum particle

Textbooks of quantum mechanics lack the concept of the past of quantum systems. Few years ago I proposed to define the past of a quantum particle according the trace it leaves.  While in many cases this definition provides a reasonable description, for a nested Mach-Zehnder interferometer it leads to a picture seemingly contradicting common sense: the particle leaves a trace in a place through which it could not pass. I will discuss recent theoretical and experimental studies of this controversial issue.