Communicating via Ignorance

Communication through a sequence of two identical, noisy, depolarising channels is impossible in conventional information theory. Surprisingly, it has been shown in the paper [1] communication becomes possible if the depolarising channels are within a quantum switch, where the order of the channels is in a quantum superposition [2,3]. We experimentally demonstrate this counterintuitive result in a quantum switch that uses polarisation to coherently control the order of two depolarising channels acting on the transverse spatial mode of a photon. We send (3.41±0.15)×10^-2 bits of information through two fully depolarising channels that are in an indefinite causal order. [4]
References:
1. D. Ebler et al, ``Enhanced Communication with the Assistance of Indefinite Causal Order,'' Phys. Rev. Lett., vol. 120, 120502 (2018).
2. G. Rubino et al., "Experimental verification of an indefinite causal order," Sci. Adv., vol. 3, e16025589 (2017).
3. K. Goswami et al., ``Indefinite Causal Order in a Quantum Switch,'' Phys. Rev. Lett. Vol. 121, 090503 (2018).
4. K. Goswami, J. Romero, and A. G. White, ``Communicating via ignorance,'' arXiv:1807.07383 (2018).