Application Of Quantum Coherent Displacement Operation In Quantum Information

Quantum information is a intercourse between quantum mechanics and computer science, which starts quite recently since 1980s. Quantum entangled state is one of the most important resource in quantum information processing.In this thesis,we investigate the application of quantum coherent displacement operations in quantum entanglement distillation, quantum linear amplifier and quantum target detection. The main work and creations are listed as follows:1.Research on displacement-assisted entanglement distillation. Photon subtraction (PS) is one of the most widely used operations for entanglement distillation. To improve the distilled entanglement in PS-based scheme, we design a realistic distillation operation with coherent state and highly transparent beam splitters.We derive a theorem to transfer a general Gaussian state from its characteristic function in phase space to photon number space. This theorem enables us to give a quantitative analysis of distilled entanglement as well as the distilling probability. The output of entanglement reached maximum while a’= ±0.30.2.Displacement-assisted quantum linear amplifiers.Quantum linear amplifier is an important tool to enhance already-known quantum communications. It can be used to protect the quantum state against photon loss.However, the gain and the probability of success in amplification is quite low. To this point, we propose to use coherent displacement operations to enhance quantum linear amplifiers. We derive the exact threshold beyond which local displacement helps to enhance distillation. We apply our state transfer theorem and numerically evaluate the dependence of quantum linear amplifiers gain on the amounts of displacement. We studied using actual displacement operations and under non-ideal conditions of single-photon sources, the gain and amplifier probability of the quantum amplifiers.We compared displacement-assisted amplifiers local Gaussian based amplifiers.3.Research on quantum target detection with quantum linear amplifiers.Quantum target detection is a scheme for detection of a potential target hidden in ambient noisy environments. However, the temporary quantum target detection requires large amounts of entangled states, which forbids its realistic application. In this thesis, we design a new scheme for quantum target detection with quantum linear amplifiers for the first time. We adjust the gain of the amplifier by regulating the permeability coefficient of the beam splitter. We obtain a method for calculations of probability of error inference.Moreover, with typical parameters in experiments, we evaluate and further prove the enhancement brought with linear amplifiers,both under low noisy and strongly noisy environments.