Post-Selection and Counterfactual Communication

Abstract

A recent quantum protocol for counterfactual communication [Y. Aharonov and L. Vaidman, Phys. Rev. A 99, 010103(R), 2019] relies on post-selection to eliminate the weak trace in the transmission channel. We show that the post-selection in this protocol also eliminates the flow of Fisher information from transmitter to receiver. However, we also show that a classical communication protocol with post-selection can be counterfactual. Hence, we argue that post-selection should not be allowed in genuine counterfactual communication. In the quantum counterfactual communication protocol, the probability of discarding an event by post-selection tends to zero with an increasing number of ideal optical components. But the counterfactual violation strength tends to infinity at a faster rate. Consequently, the quantum protocol is not counterfactual proper.

4 pages, 1 figure, As Published

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• How Quantum is Quantum Counterfactual Communication?
• Genuine Counterfactual Communication with a Nanophotonic Processor
• Direct counterfactual quantum communication protocol beyond single photon source
• Three approaches for analyzing the counterfactuality of counterfactual protocols
• Kirkwood-Dirac classical pure states
• Exploring postselection-induced quantum phenomena with time-bidirectional state formalism