Experimental observation of coherent-information superadditivity in a dephrasure channel

Abstract

We present an experimental approach to construct a dephrasure channel, which contains both dephasing and erasure noises, and can be used as an efficient tool to study the superadditivity of coherent information. By using a three-fold dephrasure channel, the superadditivity of coherent information is observed, and a substantial gap is found between the zero single-letter coherent information and zero quantum capacity. Particularly, we find that when the coherent information of n channel uses is zero, in the case of larger number of channel uses, it will become positive. These phenomena exhibit a more obvious superadditivity of coherent information than previous works, and demonstrate a higher threshold for non-zero quantum capacity. Such novel channels built in our experiment also can provide a useful platform to study the non-additive properties of coherent information and quantum channel capacity.

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• Capacity of trace decreasing quantum operations and superadditivity of coherent information for a generalized erasure channel
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• Allowing leakage can increase quantum transmission
• Multipartite entanglement to boost superadditivity of coherent information in quantum communication lines with polarization dependent losses
• Bounding the quantum capacity with flagged extensions
• Noise is resource-contextual in quantum communication
• Better transmission with lower capacity: lossy compression over quantum channels