Anomalous weak values via a single photon detection

Enrico Rebufello, Fabrizio Piacentini, Alessio Avella, Muriel Souza, Marco Gramegna, Jan Dziewior, Eliahu Cohen, Lev Vaidman, Ivo Pietro Degiovanni, Marco Genovese

Research output: Contribution to journalLetterpeer-review

7 Scopus citations


Is it possible that a measurement of a spin component of a spin-1/2 particle yields the value 100? In 1988 Aharonov, Albert and Vaidman argued that upon pre- and postselection of particular spin states, weakening the coupling of a standard measurement procedure ensures this paradoxical result1. This theoretical prediction, called weak value, was realised in numerous experiments2–9, but its meaning remains very controversial10–19, since its “anomalous” nature, i.e., the possibility to exceed the eigenvalue spectrum, as well as its “quantumness” are debated20–22. We address these questions by presenting the first experiment measuring anomalous weak values with just a single click, without the need for statistical averaging. The measurement uncertainty is significantly smaller than the gap between the measured weak value and the nearest eigenvalue. Beyond clarifying the meaning of weak values, demonstrating their non-statistical, single-particle nature, this result represents a breakthrough in understanding the foundations of quantum measurement, showing unprecedented measurement capability for further applications of weak values to quantum photonics. [Figure not available: see fulltext.]

Original languageEnglish
Article number106
Pages (from-to)106
JournalLight: Science and Applications
Issue number1
StatePublished - 25 May 2021

Bibliographical note

Funding Information:
We acknowledge the European Union’s Horizon 2020 and the EMPIR Participating States in the context of the projects 17FUN01 “BeCOMe” and 17FUN06 “SIQUST”, the European Union’s Horizon 2020 FET-OPEN project grant no. 828946 “PATHOS”, the National Science Foundation—U.S.-Israel Binational Science Foundation Grant No. 735/18. EC was supported by Grant No. FQXi-RFP-CPW-2006 from the Foundational Questions Institute and Fetzer Franklin Fund, a donor advised fund of Silicon Valley Community Foundation, the Israel Innovation Authority under Projects No. 70002 and No. 73795, the Quantum Science and Technology Program of the Israeli Council of Higher Education, and the Pazy Foundation. JD acknowledges support from the PhD program IMPRS-QST.

Publisher Copyright:
© 2021, The Author(s).


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