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Klaus Mølmer

Homodyne monitoring of postselected decay

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  • D. Tan, Washington Univ, Washington University (WUSTL), Sch Med, Dept Psychiat
  • ,
  • N. Foroozani, Washington Univ, Washington University (WUSTL), Sch Med, Dept Psychiat
  • ,
  • M. Naghiloo, Washington Univ, Washington University (WUSTL), Sch Med, Dept Psychiat
  • ,
  • A. H. Kiilerich
  • ,
  • K. Molmer
  • K. W. Murch, Georgia Inst Technol, Georgia Institute of Technology, University System of Georgia, Ctr Organ Photon & Elect, Sch Mat Sci & Engn, Sch Chem & Biochem

We use homodyne detection to monitor the radiative decay of a superconducting qubit. According to the classical theory of conditional probabilities, the excited-state population differs from an exponential decay law if it is conditioned upon a later projective qubit measurement. Quantum trajectory theory accounts for the expectation values of general observables, and we use experimental data to show how a homodyne detection signal is conditioned upon both the initial state and the finally projected state of a decaying qubit. We observe, in particular, how anomalous weak values occur in continuous weak measurement for certain pre- and postselected states. Subject to homodyne detection, the density matrix evolves in a stochastic manner, but it is restricted to a specific surface in the Bloch sphere. We show that a similar restriction applies to the information associated with the postselection, and thus bounds the predictions of the theory.

TidsskriftPhysical Review A
Antal sider9
StatusUdgivet - 3 aug. 2017

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