Entanglement-assisted classical communication can simulate classical communication without causal order

TL;DR

This paper demonstrates that entanglement-assisted classical communication can simulate classical communication without causal order, revealing a novel quantum-spacetime phenomenon and expanding understanding of quantum operations beyond relativistic causality.

Contribution

It introduces a new formulation for joint quantum operations with classical communication beyond causal order, showing entanglement can simulate non-causal classical communication within quantum mechanics.

Findings

Entanglement assists in simulating non-causal classical communication.

The formulation extends quantum operations beyond special relativistic causal order.

Entanglement reveals counter-intuitive spacetime-related properties.

Abstract

Phenomena induced by the existence of entanglement, such as nonlocal correlations, exhibit characteristic properties of quantum mechanics distinguishing from classical theories. When entanglement is accompanied by classical communication, it enhances the power of quantum operations jointly performed by two spatially separated parties. Such a power has been analyzed by the gap between the performances of joint quantum operations implementable by local operations at each party connected by classical communication with and without the assistance of entanglement. In this work, we present a new formulation for joint quantum operations connected by classical communication beyond special relativistic causal order but without entanglement and still within quantum mechanics. Using the formulation, we show that entanglement assisting classical communication necessary for implementing a class of joint quantum operations called separable maps can be interpreted to simulate "classical communication" not respecting causal order. Our results reveal a new counter-intuitive aspect of entanglement related to spacetime.