Semi-device-independent certification of quantum non-Markovianity using sequential random access codes

The characterization of multi-time correlations in open quantum systems is of fundamental importance. In this work, we investigate multi-time processes using the process matrix formalism and show that the presence of a quantum-memory environment acts as a resource in enhancing the communication capacity in sequential prepare-transform-measure quantum random access codes (QRAC). The correlated environment enables a quantum advantage to multiple parties, even with projective measurements. In particular, we show that Markovian and classical-memory processes, i.e., non-Markovian quantum processes with classical feedback from the environment, do not yield a sequential quantum advantage. In contrast, it is possible to achieve an advantage in the presence of a quantum-memory environment. Therefore, this approach allows a semi-device-independent certification of quantum non-Markovianity. As opposed to entanglement-detection criteria which require knowledge of the complete process, this method allows to certify the presence of a quantum-memory environment from the observed measurement statistics. Moreover, quantum memory ameliorates the unambiguous certifiable region of unsharp instruments in a semi-device-independent manner.