Anomalous weak values via a single photon detection

• Published in: Light, science & applications Vol. 10; no. 1; p. 106
• Main Authors: Rebufello, Enrico, Piacentini, Fabrizio, Avella, Alessio, Souza, Muriel A. de, Gramegna, Marco, Dziewior, Jan, Cohen, Eliahu, Vaidman, Lev, Degiovanni, Ivo Pietro, Genovese, Marco
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 25.05.2021; Springer Nature B.V; Nature Publishing Group
• Subjects: 639/766/400/3925; 639/766/400/482; Applied and Technical Physics; Atomic; Classical and Continuum Physics; Eigenvalues; Lasers; Letter; Molecular; Optical and Plasma Physics; Optical Devices; Optics; Photonics; Physics; Physics and Astronomy; Statistics
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/s41377-021-00539-0

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 result 1 . This theoretical prediction, called weak value , was realised in numerous experiments 2 – 9 , but its meaning remains very controversial 10 – 19 , since its “anomalous” nature, i.e., the possibility to exceed the eigenvalue spectrum, as well as its “quantumness” are debated 20 – 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.