Pre- and postselected quantum states: Density matrices, tomography, and Kraus operators

Sandu Popescu, Ralph F Silva*, Yelena A Guryanova, Nicolas Brunner, Noah Linden, A J Short

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

32 Citations (Scopus)


We present a general formalism for characterizing 2-time quantum states, describing pre- and postselected quantum systems. The most general 2-time state is characterized by a "density vector" that is independent of measurements performed between the preparation and postselection. We provide a method for performing tomography of an unknown 2-time density vector. This procedure, which cannot be implemented by weak or projective measurements, brings new insight to the fundamental role played by Kraus operators in quantum measurements. Finally, after showing that general states and measurements are isomorphic, we show that any measurement on a 2-time state can be mapped to a measurement on a preselected bipartite state
Original languageEnglish
Article number012121
JournalPhysical Review A: Atomic, Molecular and Optical Physics
Issue number1
Publication statusPublished - 23 Jan 2014


  • quantum
  • foundations
  • pre and postselection


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