Interaction-Free Effects Between Distant Atoms

Yakir Aharonov, Eliahu Cohen*, Avshalom C. Elitzur, Lee Smolin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


A Gedanken experiment is presented where an excited and a ground-state atom are positioned such that, within the former’s half-life time, they exchange a photon with 50% probability. A measurement of their energy state will therefore indicate in 50% of the cases that no photon was exchanged. Yet other measurements would reveal that, by the mere possibility of exchange, the two atoms have become entangled. Consequently, the “no exchange” result, apparently precluding entanglement, is non-locally established between the atoms by this very entanglement. This quantum-mechanical version of the ancient Liar Paradox can be realized with already existing transmission schemes, with the addition of Bell’s theorem applied to the no-exchange cases. Under appropriate probabilities, the initially-excited atom, still excited, can be entangled with additional atoms time and again, or alternatively, exert multipartite nonlocal correlations in an interaction free manner. When densely repeated several times, this result also gives rise to the Quantum Zeno effect, again exerted between distant atoms without photon exchange. We discuss these experiments as variants of interaction-free-measurement, now generalized for both spatial and temporal uncertainties. We next employ weak measurements for elucidating the paradox. Interpretational issues are discussed in the conclusion, and a resolution is offered within the Two-State Vector Formalism and its new Heisenberg framework.

Original languageEnglish
Pages (from-to)1-16
Number of pages16
JournalFoundations of Physics
Issue number1
StatePublished - 1 Jan 2018


FundersFunder number
Innovation, Science and Economic Development Canada
Government of Canada
European Research Council
Israel Science Foundation1311/14
Ontario Ministry of Research and Innovation
Institut Périmètre de physique théorique


    • Entanglement
    • Interaction free measurement
    • Nonlocality
    • Quantum Zeno effect
    • Weak measurements


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