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We propose an efficient decomposition scheme for a quantum receiver that attains the Helstrom bound in the low-photon regime for discriminating binary coherent states. Our method, which avoids feedback as used in Dolinar's case, breaks down nonlinear operations into basic gates used in continuous-variable quantum computation. We account for realistic conditions by examining the impact of photon loss and imperfect photon detection, including the presence of dark counts, while presenting squeezing as a technique to mitigate these noise sources and maintain the advantage over SQL. Our scheme motivates testing quantum advantages with cubic-phase gates and designing photonic quantum computers to optimize symbol-by-symbol measurements in optical communication., Comment: 8 pages, 7 figures

Counterfactual quantum communication is one of the most interesting facets of quantum communication, allowing two parties to communicate without any transmission of quantum or classical particles between the parties involved in the communication process. This aspect of quantum communication originates from the interaction-free measurements where the chained quantum Zeno effect plays an important role. Here, we propose a new counterfactual quantum communication protocol for transmitting an entangled state from a pair of electrons to two independent photons. Interestingly, the protocol proposed here shows that the counterfactual method can be employed to transfer information from house qubits to flying qubits. Following this, we show that the protocol finds uses in building quantum repeaters leading to a counterfactual quantum network, enabling counterfactual communication over a linear quantum network., Comment: It's shown that counterfactual quantum repeaters can be built and used in quantum networks

In this paper, we address the generation of a two-pair frequency entangled state using type-0 spontaneous parametric down-conversion process in a dual periodically poled lithium niobate waveguide. We show that, by suitable domain engineering with two periods of quasi-phase matching grating, it is possible to achieve a frequency entangled state with two different pairs of frequencies. Numerical simulations show that the output state can be maximally entangled. We also perform numerical simulations to address other interesting and useful entangled states which can be generated with the help of our scheme. The proposed scheme can help create efficient photonic setups required for quantum communication systems and can have various applications considering the increasing interests of energy-time entanglement in quantum information regime., Comment: 7 pages, 5 figures

Quantum communication is one of the cutting-edge research areas today, where the scheme of Remote State Preparation (RSP) has caught significant attention of researchers. A number of different schemes of RSP have already been proposed so far. We propose here a hierarchical RSP protocol for sending a two-qubit entangled state using a seven-qubit highly entangled state derived from Brown et al. state. We have also studied here the effects of two well known noise models namely amplitude damping (AD) and phase damping (PD) that affect the quantum communication channel used for the protocol. An investigation on the variation of fidelity of the state with respect to the noise operator and the receiver is made. PD noise is found to affect the fidelity more than the AD noise and the higher power receiver, obtains the state with higher fidelity than the lower power receiver under the effect of noise. To the best of our knowledge, we believe that we have achieved the highest fidelity for the higher power receiver, 0.89 in the presence of maximum AD noise and 0.72 in the presence of maximum PD noise, compared to all the previously proposed RSP protocols in noisy environments. The study of noise is described in a very pedagogical manner for better understanding of the application of noise models to a communication protocol., Comment: 2 figures, 9 pages