Quantum nature of laser light

J. Jeffers, D.T. Pegg

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)
32 Downloads (Pure)


All compositions of a mixed-state density operator are equivalent for the prediction of the probabilities of future outcomes of measurements. For retrodiction, however, this is not the case. The retrodictive formalism of quantum mechanics provides a criterion for deciding that some compositions are fictional. Fictional compositions do not contain preparation device operators, that is operators corresponding to states that could have been prepared. We apply this to Mølmer's controversial conjecture that optical coherences in laser light are a fiction and find agreement with his conjecture. We generalize Mølmer's derivation of the interference between two lasers to avoid the use of any fictional states. We also examine another possible method for discriminating between coherent states and photon number states in laser light and find that it does not work, with the equivalence for prediction saved by entanglement.
Original languageEnglish
Pages (from-to)1835-1856
Number of pages21
JournalJournal of Modern Optics
Issue number13
Publication statusPublished - 10 Sept 2005


  • quantum
  • laser
  • light
  • optics
  • quantum physics
  • laser light
  • quantum mechanics
  • photon


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