Quantum non-barking dogs

Sara Walker, Paul Davies, Prasant Samantray, Yakir Aharonov

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Quantum weak measurements with states both pre- and post-selected offer a window into a hitherto neglected sector of quantum mechanics. A class of such systems involves time dependent evolution with transitions possible. In this paper we explore two very simple systems in this class. The first is a toy model representing the decay of an excited atom. The second is the tunneling of a particle through a barrier. The post-selection criteria are chosen as follows: at the final time, the atom remains in its initial excited state for the first example and the particle remains behind the barrier for the second. We then ask what weak values are predicted in the physical environment of the atom (to which no net energy has been transferred) and in the region beyond the barrier (to which the particle has not tunneled). Thus, just as the dog that didnt bark in Arthur Conan Doyles story Silver Blaze gave Sherlock Holmes meaningful information about the dogs non-canine environment, here we probe whether the particle that has not decayed or has not tunneled can provide measurable information about physical changes in the environment. Previous work suggests that very large weak values might arise in these regions for long durations between pre- and post-selection times. Our calculations reveal some distinct differences between the two model systems.

Original languageEnglish (US)
Article number063026
JournalNew Journal of Physics
StatePublished - Jun 2014


  • post-selection
  • quantum mechanics
  • weak measurement

ASJC Scopus subject areas

  • General Physics and Astronomy


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