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We experimentally demonstrate a new measurement scheme for the discrimination of two coherent states. The measurement scheme is based on a displacement operation followed by a photon-number-resolving detector, and we show that it outperforms the standard homodyne detector which we, in addition, prove to be optimal within all Gaussian operations including… (More)
We present a new protocol for quantum key distribution using discrete phase-shift encoding with continuous variables. The novelty of the protocol is multi letter alphabets represented by coherent states of light with fixed amplitude and variable phase. Information is encoded in the phase of a coherent states which can be chosen from a regular discrete set… (More)
A new quantum cryptography protocol, based on all unselected states of a qubit as a sort of alphabet with continuous set of letters, is proposed. Its effectiveness is calculated and shown to be essentially higher than those of the other known protocols.
We address the long-standing problem of discriminating coherent states with the minimum error rate. We show an optimum receiver for coherent states which admits a relatively simple implementation with current technologies. The receiver is based on multichannel splitting of the signal, followed by feed-forward signal displacement and photon-counting… (More)
In our continuous variable quantum key distribution (QKD) scheme, the homodyne detection setup requires balancing the intensity of an incident beam between two photodiodes. Realistic lens systems are insufficient to provide a spatially stable focus in the presence of large spatial beam-jitter caused by atmospheric transmission. We therefore present an… (More)
We present the scheme of compatible quantum information analysis of the quantum key distribution (QKD) protocols, which give answers to the following questions: is it possible to improve the quantum bit error rate (QBER) of the 6-state protocol by employing more states, up to infinity, and can we essentially improve the QBER if the multidimensional Hilbert… (More)
The presented probabilistic scheme for discrimination of optical coherent states consists of an optimized displacement followed by postselection of a photon number resolving measurement. The scheme outperforms the homodyne receiver in theory and experiment.