Efficient superdense coding in the presence of non-Markovian noise

: Liu BH, Hu XM, Huang YF, Li CF, Guo GC, Karlsson A, Laine EM, Maniscalco S, Macchiavello C, Piilo J

Publisher: EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY

: 2016

: EPL

: EPL-EUROPHYS LETT

: ARTN 10005

: 114

: 1

: 6

: 0295-5075

: 1286-4854

DOI: https://doi.org/10.1209/0295-5075/114/10005

Many quantum information tasks rely on entanglement, which is used as a resource, for example, to enable efficient and secure communication. Typically, noise, accompanied by loss of entanglement, reduces the efficiency of quantum protocols. We develop and demonstrate experimentally a superdense coding scheme with noise, where the decrease of entanglement in Alice's encoding state does not reduce the efficiency of the information transmission. Having an almost fully dephased classical two-photon polarization state at the time of encoding with concurrence of 0.163 +/- 0.007, we reach values of mutual information close to 1.52 +/- 0.02 (1.89 +/- 0.05) with 3-state (4-state) encoding. This high efficiency relies both on non-Markovian features, that Bob exploits just before his Bell state measurement, and on very high visibility (99.6% +/- 0.1%) of the Hong-Ou-Mandel interference within the experimental set-up. Our proof-of-principle results with measurements on mutual information pave the way for exploiting non-Markovianity to improve the efficiency and security of quantum information processing tasks. Copyright (C) EPLA, 2016