5 research outputs found

    Programming the Kennedy Receiver for Capacity Maximization versus Minimizing One-shot Error Probability

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    We find the capacity attained by the Kennedy receiver for coherent-state BPSK when the symbol prior p and pre-detection displacement are optimized. The optimal displacement is different than what minimizes error probability for single-shot BPSK state discrimination.Comment: Updating email address format for this replacement submissio

    Linear optics and photodetection achieve near-optimal unambiguous coherent state discrimination

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    Coherent states of the quantum electromagnetic field, the quantum description of ideal laser light, are prime candidates as information carriers for optical communications. A large body of literature exists on their quantum-limited estimation and discrimination. However, very little is known about the practical realizations of receivers for unambiguous state discrimination (USD) of coherent states. Here we fill this gap and outline a theory of USD with receivers that are allowed to employ: passive multimode linear optics, phase-space displacements, auxiliary vacuum modes, and on-off photon detection. Our results indicate that, in some regimes, these currently-available optical components are typically sufficient to achieve near-optimal unambiguous discrimination of multiple, multimode coherent states.Comment: 18 pages, 10 figures, and 2 tables. Appendices included. Additional references added. Comments welcome

    Superadditivity of Quantum Channel Coding Rate with Finite Blocklength Joint Measurements

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    The maximum rate at which classical information can be reliably transmitted per use of a quantum channel strictly increases in general with NN, the number of channel outputs that are detected jointly by the quantum joint-detection receiver (JDR). This phenomenon is known as superadditivity of the maximum achievable information rate over a quantum channel. We study this phenomenon for a pure-state classical-quantum (cq) channel and provide a lower bound on CN/NC_N/N, the maximum information rate when the JDR is restricted to making joint measurements over no more than NN quantum channel outputs, while allowing arbitrary classical error correction. We also show the appearance of a superadditivity phenomenon---of mathematical resemblance to the aforesaid problem---in the channel capacity of a classical discrete memoryless channel (DMC) when a concatenated coding scheme is employed, and the inner decoder is forced to make hard decisions on NN-length inner codewords. Using this correspondence, we develop a unifying framework for the above two notions of superadditivity, and show that for our lower bound to CN/NC_N/N to be equal to a given fraction of the asymptotic capacity CC of the respective channel, NN must be proportional to V/C2V/C^2, where VV is the respective channel dispersion quantity.Comment: To appear in IEEE Transactions on Information Theor
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