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Measuring the size of a Schroedinger cat state

Florian Marquardt·Benjamin Abel·Jan von Delft
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Abstract

We propose a measure for the "size" of a Schroedinger cat state, i.e. a quantum superposition of two many-body states with (supposedly) macroscopically distinct properties, by counting how many single-particle operations are needed to map one state onto the other. This definition gives sensible results for simple, analytically tractable cases and is consistent with a previous definition restricted to Greenberger-Horne-Zeilinger-like states. We apply our measure to the experimentally relevant, nontrivial example of a superconducting three-junction flux qubit put into a superposition of left- and right-circulating supercurrent states and find this Schroedinger cat to be surprisingly small.

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Florian Marquardt, Benjamin Abel, Jan von Delft. 2006-09-01. Measuring the size of a Schroedinger cat state. https://doi.org/10.1103/physreva.78.012109

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