It has been conjectured that counterfactual communication is impossible, even for post-selected quantum particles.
A team of researchers has strongly challenged this by proposing precisely such a counterfactual scheme where—unambiguously—none of Alice’s photons that correctly contribute to her information about Bob’s message have been to Bob.
They demonstrated counterfactuality experimentally by means of weak measurements, and conceptually using consistent histories—thus simultaneously satisfying both criteria without loopholes. Importantly, the fidelity of Alice learning Bob’s bit can be made arbitrarily close to unity.
The paper has been published in npj Quantum Information.
