Protective measurements: Extracting the expectation value by measuring a single particle

Fabrizio Piacentini, Alessio Avella, Enrico Rebufello, Salvatore Virzì, Rudi Lussana, Federica Villa, Alberto Tosi, Marco Gramegna, Giorgio Brida, Eliahu Cohen, Lev Vaidman, Ivo Pietro Degiovanni, Marco Genovese

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


In quantum mechanics, the eigenvalues and their corresponding probabilities specify the expectation value of a physical observable, which is known to be a statistical property related to large ensembles of particles. In contrast to this paradigm, we demonstrate a unique method allowing to extract the expectation value of a single particle, namely, the polarisation of a single protected photon, with a single experiment. This is the first realisation of quantum protective measurements.

Original languageEnglish
Title of host publicationQuantum Technologies 2018
EditorsMiles J. Padgett, Andrew J. Shields, Jurgen Stuhler
ISBN (Electronic)9781510618749
StatePublished - 2018
Externally publishedYes
EventQuantum Technologies 2018 - Strasbourg, France
Duration: 23 Apr 201825 Apr 2018

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceQuantum Technologies 2018

Bibliographical note

Publisher Copyright:
© 2018 SPIE.


  • expectation value
  • foundations of quantum mechanics
  • protective measurements
  • quantum metrology
  • quantum optics
  • single photons


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