Robust certification of quantum instruments through a sequential communication game

Abstract: We propose a communication game in the sequential measurement scenario, involving a sender and two receivers with restricted collaboration among the latter parties. In the framework of the prepare-transform-measure scenario, we find a prominent quantum advantage in the receiver's decoding of the message originally encoded by the sender. We show that an optimal trade-off between the success probabilities of the two receivers enables self-testing of the sender's state preparation, the first receiver's instruments, and the measurement device of the second receiver. Our protocol enables a more robust certification of the unsharp measurement parameter of the first receiver compared to the protocol without collaboration among the receivers. We further generalize our game to higher-dimensional systems, revealing greater quantum advantage with an increase in dimensions.