Measurement incompatibility and quantum advantage in communication

Measurement incompatibility stipulates the existence of quantum measurements that cannot be carried out simultaneously on single systems. We show that the set of input-output probabilities obtained from d-dimensional classical systems assisted with shared randomness is the same as the set obtained from d-dimensional quantum strategies restricted to compatible measurements with shared randomness in any communication scenario. Thus, measurement incompatibility is necessary for quantum advantage in communication, and any quantum advantage (with or without shared randomness) in communication acts as a witness to the incompatibility of the measurements at the receiver's end in a semi-device-independent way. We introduce a class of communication tasks-a general version of random access codes-to witness incompatibility of an arbitrary number of quantum measurements with arbitrary outcomes acting on d-dimensional systems and provide generic upper bounds on the success metric of these tasks for compatible measurements. We identify all sets of three incompatible rank-one projective qubit measurements that random access codes can witness. Finally, we present the generic relationship between different sets of probability distributions-classical, quantum with or without shared randomness, and quantum restricted to compatible measurements with or without shared randomness-produced in communication scenarios.

Automated summary

This article investigates the phenomenon of measurement incompatibility in quantum communication, demonstrating that the input-output probabilities for classical systems with shared randomness are equivalent to those for d-dimensional quantum strategies with shared randomness and compatible measurements in any communication scenario. Therefore, measurement incompatibility is necessary for quantum advantage in communication, and any quantum advantage serves as evidence of measurement incompatibility at the receiver's end in a semi-device-independent manner. The article introduces a class of communication tasks, a general version of random access codes, to witness the incompatibility of arbitrary numbers of quantum measurements with arbitrary outcomes on d-dimensional systems, providing generic upper bounds on the success metric for compatible measurements. The sets of three incompatible rank-one projective qubit measurements that can be witnessed by random access codes are identified. Finally, the article presents the generic relationship between different sets of probability distributions-classical, quantum with or without shared randomness, and quantum restricted to compatible measurements with or without shared randomness-produced in communication scenarios.