TL;DR
This paper critically examines the concept of counterfactuality in quantum protocols, defining it and analyzing which protocols genuinely qualify as counterfactual based on their measurement interactions.
Contribution
It provides a clear definition of counterfactuality and evaluates existing protocols, distinguishing between those that are truly counterfactual and those that are not.
Findings
Interaction-free measurement of an object is counterfactual.
Protocols measuring the presence of an object are counterfactual.
Quantum direct communication protocols are not counterfactual.
Abstract
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.
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Taxonomy
TopicsQuantum Information and Cryptography · Quantum Mechanics and Applications · Quantum Computing Algorithms and Architecture