Graph explorer

Quantum Reading Capacity

The readout of a classical memory can be modelled as a problem of quantum channel discrimination, where a decoder retrieves information by distinguishing the different quantum channels encoded in each cell of the memory [S. Pirandola, Phys. Rev. Lett. 106, 090504 (2011)]. In the case of optical memories, such as CDs and DVDs, this discrimination involves lossy bosonic channels and can be remarkably boosted by the use of nonclassical light (quantum reading). Here we generalize these concepts by extending the model of memory from single-cell to multi-cell encoding. In general, information is stored in a block of cells by using a channel-codeword, i.e., a sequence of channels chosen according to a classical code. Correspondingly, the readout of data is realized by a process of "parallel" channel discrimination, where the entire block of cells is probed simultaneously and decoded via an optimal collective measurement. In the limit of an infinite block we define the quantum reading capacity of the memory, quantifying the maximum number of readable bits per cell. This notion of capacity is nontrivial when we suitably constrain the physical resources of the decoder. For optical me