Conditions for degradability of tripartite quantum states

Chi Hang Fred Fung, Chi Kwong Li, Nung Sing Sze, H. F. Chau

Research output: Journal article publicationJournal articleAcademic researchpeer-review

1 Citation (Scopus)


Alice, Bob, and Eve share a pure quantum state. We introduce the notion of state degradability by asking whether the joint density of Alice and Eve can be transformed to the joint density of Alice and Bob by processing Eve's part through a quantum channel, in order words, degrading Eve. We prove necessary and sufficient conditions for state degradability and provide an efficient method to quickly rule out degradability for a given state. The problem of determining degradability of states is different from that of quantum channels, although the notion is similar. One application of state degradability is that it can be used to test channel degradability. In particular, the degradability of the output state of a channel obtained from the maximally entangled input state gives information about the degradability of the channel.
Original languageEnglish
Article number115306
JournalJournal of Physics A: Mathematical and Theoretical
Issue number11
Publication statusPublished - 21 Mar 2014


  • quantum communication
  • quantum cryptography
  • quantum entanglement
  • quantum information
  • transformability of states

ASJC Scopus subject areas

  • Statistical and Nonlinear Physics
  • Statistics and Probability
  • Modelling and Simulation
  • Mathematical Physics
  • Physics and Astronomy(all)

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