Quantum communication in a superposition of causal orders

TL;DR

This paper demonstrates that quantum communication protocols exploiting superpositions of causal orders can significantly improve quantum information transmission over noisy channels, surpassing classical limitations.

Contribution

It introduces a method to enhance quantum communication by using indefinite causal order, showing advantages over traditional fixed-order protocols.

Findings

Superposition of causal orders enables error-free transmission with 25% probability.

Quantum information transfer is improved in partially dephasing channels when using superpositions.

Superposed causal order can transmit more quantum information than individual channels alone.

Abstract

Quantum mechanics allows for situations where the relative order between two processes is entangled with a quantum degree of freedom. Here we show that such entanglement can enhance the ability to transmit quantum information over noisy communication channels. We consider two completely dephasing channels, which in normal conditions are unable to transmit any quantum information. We show that, when the two channels are traversed in an indefinite order, a quantum bit sent through them has a 25% probability to reach the receiver without any error. For partially dephasing channels, a similar advantage takes place deterministically: the amount of quantum information that can travel through two channels in a superposition of orders can be larger than the amount of quantum information that can travel through each channel individually.