Target Detection Theory Based On X-type Quantum States

It is a hot research direction to perform target detection based on ba-sic principles of quantum mechanics nowadays. It can be said that quantum target detection (QTD) extends applications of quantum mechanics, quantum information and quantum computing. In this thesis, we consider the target’s position accuracy, by measuring the phase accuracy with the relationship be-tween optical path length and phase displacement. We investigate QTD by the use of orthogonal projection and parity measurement schemes for the two cases of lossless and lossy environments, respectively. We explore the role of quantum correlations in QTD by making use of a kind of special X-type quantum state,so-called Werner states, as input states of the system under our consideration. By adjusting the state parameters one can make X-type quantum states be an entangled quantum state, or a non-entangled quantum state. The main results obtained in this thesis are as follows:1. We study the influence of quantum correlations on the precision of phase measurement by the use of the orthogonal projection measurement scheme in a free-of-photon-loss environment. It is found that the free-of-entanglement quantum correlations can enhance the precision of phase mea-surement. In a free-of-loss environment, we obtain the relationships between the phase measurement error, the state parameters, photon loss parameter, the photon number, as well as the object phase. It is indicated that phase measurement error changes periodically with respect to the phase shift φ; For a given value of the state parameter c, a larger number of photons correspond to a smaller phase measurement error, then one can get higher detection preci-sion; For a fixed photon number state, the parameter c values greater the phase measurement precision enhances with the increase of the state parameter c. In particular, it is found that in the free-of-entanglement regime0≤c≤1/63, quantum correlations can be used to improve measurement accuracy.2. We investigate the role of quantum correlations in phase measurement by the use of the orthogonal projection measurement scheme in a photon-loss environment. It is found that both quantum correlations and the number of photons of the initial state seriously affect the precision of phase measurement. We obtain relations between the phase measurement precision and the state parameters, the loss parameter, the number of photons and the target phase relation:It is indicated that fewer photons, the impact of changes in the value of the loss of the minimum phase accuracy is smaller; When the photon number increases, the impact of the loss of the minimum phase accuracy becomes very large.3. We study effect of quantum correlations on the precision of phase mea-surement by the use of the parity-measurement scheme of the photon number. We obtain the relationships between phase measurement precision error and the state parameters, the number of photons, target phase for the photon-lossless and-lossy cases. It is found that the increase of the state parameter c can improve the phase measurement accuracy. In the presence of the photon loss, it is indicated that the influence of the photon loss to phase measurement error is a dramatic increase with the increase of the number of photons.4. We compare the results for the case of the orthogonal projection mea-surement scheme with those for the case of the parity measurement. It is found that the precision of the phase measurement for the case of the orthogonal pro-jection measurement scheme is smaller than that of the parity measurement case. By adjusting the parameters of the states and the signal photons count, it is indicated that the precision of the phase measurement can break through the standard quantum limit, and close to the Heisenberg limit.