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Postprocessing of quantum instruments
Tekijät: Leppäjärvi Leevi, Sedlak Michal
Kustantaja: AMER PHYSICAL SOC
Julkaisuvuosi: 2021
Journal: Physical Review A
Tietokannassa oleva lehden nimi: PHYSICAL REVIEW A
Lehden akronyymi: PHYS REV A
Artikkelin numero: ARTN 022615
Vuosikerta: 103
Numero: 2
Sivujen määrä: 13
ISSN: 2469-9926
DOI: https://doi.org/10.1103/PhysRevA.103.022615
Verkko-osoite: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.103.022615
Tiivistelmä
Studying sequential measurements is of the utmost importance to both the foundational aspects of quantum theory and the practical implementations of quantum technologies, with both of these applications being abstractly described by the concatenation of quantum instruments into a sequence of a certain length. In general, the choice of instrument at any given step in the sequence can be conditionally chosen based on the classical results of all preceding instruments. For two instruments in a sequence we consider the conditional second instrument as an effective way of postprocessing the first instrument into a new one. This is similar to how a measurement described by a positive operator-valued measure (POVM) can be postprocessed into another by way of classical randomization of its outcomes using a stochastic matrix. In this work we study the postprocessing relation of instruments and the partial order it induces on their equivalence classes. We characterize the greatest and the least element of this order, give examples of postprocessings between different types of instruments, and draw connections between postprocessings of some of these instruments and their induced POVMs.
Studying sequential measurements is of the utmost importance to both the foundational aspects of quantum theory and the practical implementations of quantum technologies, with both of these applications being abstractly described by the concatenation of quantum instruments into a sequence of a certain length. In general, the choice of instrument at any given step in the sequence can be conditionally chosen based on the classical results of all preceding instruments. For two instruments in a sequence we consider the conditional second instrument as an effective way of postprocessing the first instrument into a new one. This is similar to how a measurement described by a positive operator-valued measure (POVM) can be postprocessed into another by way of classical randomization of its outcomes using a stochastic matrix. In this work we study the postprocessing relation of instruments and the partial order it induces on their equivalence classes. We characterize the greatest and the least element of this order, give examples of postprocessings between different types of instruments, and draw connections between postprocessings of some of these instruments and their induced POVMs.
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