Quantum communication with photon-number entangled states and realistic photodetection

Abstract

We address the effects of realistic photodetection, with nonunit quantum efficiency and background noise (dark counts), on the performances of quantum communication schemes based on photon-number entangled states (PNES). We consider channels based on Gaussian twin-beam states (TWB) and nonGaussian two-mode coherent states (TMC) and evaluate the channel capacity by optimizing the bit discrimination threshold. We found that TWB-based channels are more robust against noise than TMCbased ones and that this result is almost independent on the statistics of dark counts.

Heisenberg-limited interferometry with pair coherent states and parity measurements

“…The PCS were first discussed in the quantum optics literature by Agarwal [13] and it has recently been shown theoretically that such states could be produced by non-degenerate parametric oscillators [14]. The states have been discussed with many applications in mind, such as violations of EPR-Bell-type inequalities [15], and continuous variable quantum information processing such as quantum teleportation [16], quantum communication [17], and quantum cryptography [18] ϕ ∆ = For the smaller ϕ we have sensitivity essentially at the HL whereas even for the larger value, apart from the large deviations for certain average photon numbers, the phase uncertainty is still fairly close to the Heisenberg limit. The PCS appear to be more robust for parity based interferometry than do the two-mode squeezed vacuum states.…”

“…The PCS were first discussed in the quantum optics literature by Agarwal [13] and it has recently been shown theoretically that such states could be produced by non-degenerate parametric oscillators [14]. The states have been discussed with many applications in mind, such as violations of EPR-Bell-type inequalities [15], and continuous variable quantum information processing such as quantum teleportation [16], quantum communication [17], and quantum cryptography [18] though in the last two references the PCS are instead called two-mode coherently correlated states, or states of correlated twin laser beams. Unlike the TMSVS, the PCS are non-Gaussian states.…”

Trusted Noise in Continuous-Variable Quantum Key Distribution: A Threat and a Defense

“…Typically the continuous quadrature observables are used to encode key bits, and subsequently, the homodyne detection of the quadrature (or heterodyne measurement of two complementary quadratures simultaneously) is applied contrary to the photon-counting measurement in DV QKD. Alternatively, polarization [23] or photon-number coding [24][25][26][27][28] can in principle be used. The preliminary version of CV QKD was firstly suggested [29] and studied against particular eavesdropping strategies [30] by Ralph based on the binary quadrature displacement of coherent state produced by a laser or two-mode quadrature-squeezed states, which can be produced by an optical parametric oscillator.…”

Improvement in error performance of optical communication system using quantum detection theory

“…For 20 km transmission distance the system has measured 8.65 Mbit/s and 5.98 Mbit/s secure key rates for point to point and multi-user arrangement, respectively, and also up to 12 Mbit/s for a lossless channel. Usenko et al [8] examined quantum communication schemes based on photon number entanglement based on Gaussian channel states and also studied detection noise and quantum efficiency. Shukla et al [9] discussed about hierarchical quantum communication and its possible realization scheme to 4 qubit entangled states.…”