5 research outputs found
Programming the Kennedy Receiver for Capacity Maximization versus Minimizing One-shot Error Probability
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
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
The maximum rate at which classical information can be reliably transmitted
per use of a quantum channel strictly increases in general with , 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
, the maximum information rate when the JDR is restricted to making
joint measurements over no more than 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 -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 to be equal to a
given fraction of the asymptotic capacity of the respective channel,
must be proportional to , where is the respective channel dispersion
quantity.Comment: To appear in IEEE Transactions on Information Theor