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International Journal of Quantum Information

“Counterfactual” quantum protocols

Lev Vaidman A

Published May 21, 2016• 10 citations
Publisher

Abstract

The counterfactuality of recently proposed protocols is analyzed. A definition of “counterfactuality” is offered and it is argued that an interaction-free measurement (IFM) of the presence of an opaque object can be named “counterfactual”, while proposed “counterfactual” measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name “counterfactual” is not appropriate for recent “counterfactual” protocols which transfer quantum states by quantum direct communication.

DOI
10.1142/s0219749916400128

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{open_quotes}Interaction-free{close_quotes} measurements of quantum objects?

Andrew G. White, Paul G. Kwiat, Daniel F. V. James

It is now well established that the presence of an opaque classical object can be unambiguously determined by an {open_quotes}interaction-free{close_quotes} measurement (IFM), where the object and the probe never directly interact. For quantum objects, we examine {open_quotes}interaction-free{close_quotes} measurement (the object wavefunction is unchanged) and {open_quotes}interaction-free{close_quotes} preparation (the object wavefunction is changed without physical interaction) and find that in general, neither is possible. We propose using high efficiency IFM{close_quote}s as a quantum information bus to connect disjoint quantum systems. {copyright} {ital 1999 American Institute of Physics.}

AIP conference proceedings•Mar 1, 1999•0 citations
The counterfactuality of recently proposed protocols is analyzed. A definition of “counterfactuality” is offered and it is argued that an interaction-free measurement (IFM) of the presence of an opaque object can be named “counterfactual”, while proposed “counterfactual” measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name “counterfactual” is not appropriate for recent “counterfactual” protocols which transfer quantum states by quantum direct communication.
The counterfactuality of recently proposed protocols is analyzed. A definition of `counterfactuality' is offered and it is argued that an interaction-free measurement of the presence of an opaque object can be named `counterfactual', while proposed "counterfactual" measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name `counterfactual' is not appropriate for recent "counterfactual" protocols which transfer quantum states by quantum direct communication.
Counterfactual communication, i.e., a communication without particles traveling in the transmission channel, is a bizarre quantum effect. Starting from interaction-free measurements many protocols achieving various tasks from counterfactual cryptography to counterfactual transfer of quantum states were proposed and implemented in experiments. However, the meaning of conterfactuality in various protocols remains a controversial topic. A simple error-free counterfactual protocol is proposed. This protocol and its modification are used as a test bed for analysis of the meaning of counterfactuality to clarify the counterfactuality status of various counterfactual proposals.
In a recent paper, Griffiths [Phys. Rev. A 107, 062219 (2023)] analyzed a protocol for transmission of information between two parties introduced by Salih et al. [Phys. Rev. Lett. 110, 170502 (2013)]. There is a considerable controversy about the counterfactuality of this protocol, and Griffiths suggested to resolve it by introducing a new measure of channel usage, which he called ``Cost.'' I argue that this measure is not appropriate because the original interaction-free measurement protocol which triggered the definition of the concept of counterfactuality is not counterfactual according to this measure.
It is now well established that the presence of an opaque classical object can be unambiguously determined by an "interaction-free" measurement (IFM), where the object and the probe never directly interact. For quantum objects, we examine "interaction-free" measurement (the object wavefunction is unchanged) and "interaction-free" preparation (the object wavefunction is changed without physical interaction) and find that in general, neither is possible. We propose using high efficiency IFM's as a quantum information bus to connect disjoint quantum systems.
It is now well established that the presence of an opaque classical object can be unambiguously determined by an {open_quotes}interaction-free{close_quotes} measurement (IFM), where the object and the probe never directly interact. For quantum objects, we examine {open_quotes}interaction-free{close_quotes} measurement (the object wavefunction is unchanged) and {open_quotes}interaction-free{close_quotes} preparation (the object wavefunction is changed without physical interaction) and find that in general, neither is possible. We propose using high efficiency IFM{close_quote}s as a quantum information bus to connect disjoint quantum systems. {copyright} {ital 1999 American Institute of Physics.}