Paradoxical consequences of multipath coherence: Perfect interactionfree measurements
Abstract
Quantum coherence can be used to infer the presence of a detector without triggering it. Here we point out that according to quantum mechanics, such interactionfree measurements cannot be perfect, i.e., in a singleshot... [ view full abstract ]
Quantum coherence can be used to infer the presence of a detector without triggering it. Here we point out that according to quantum mechanics, such interactionfree measurements cannot be perfect, i.e., in a singleshot experiment one has strictly positive probability to activate the detector. We formalize the extent to which such measurements are forbidden by deriving a tradeoff relation between the probability of activation and the probability of an inconclusive interactionfree measurement. Our description of interactionfree measurements
is theory independent and allows derivations of similar relations in models generalizing quantum mechanics. We provide the tradeoff for the density cube formalism, which extends the quantum model by permitting coherence between more than two paths. The tradeoff obtained hints at the possibility of perfect interactionfree measurements and indeed we construct their explicit examples. Such measurements open up a paradoxical possibility where we can learn by means of interference about the presence of an object in a given location without ever detecting a probing particle in that location. We therefore propose that absence of perfect interactionfree measurement is a natural postulate expected to hold in all physical theories. As shown, it holds in quantum mechanics and excludes the models with multipath coherence.
Authors

Zhuo Zhao
(School of Physical and Mathematical Sciences, Nanyang Technological University)

Spandan Mondal
(Indian Institute of Science, Bangalore)

Marcin Markiewicz
(Institute of Physics, Jagiellonian University, Krakow)

Adam Rutkowski
(Institute of Theoretical Physics and Astrophysics, Faculty of Mathematics, Physics and Informatics, University of Gdansk)

Borivoje Dakic
(Institute of Quantum Optics and Quantum Information, Austrian Academy of Sciences, Vienna)

Wieslaw Laskowski
(Institute of Theoretical Physics and Astrophysics, Faculty of Mathematics, Physics and Informatics, University of Gdansk)

Tomasz Paterek
(Nanyang Technological University)
Topic Areas
Quantum information processing and computing , Quantum communication , Fundamental science for quantum technologies
Session
PS1 » Poster Session (13:30  Wednesday, 5th September, Hall)
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