Studies On Quantum Dense Coding With A Bell-class State, And Quantum Discord Of A W-class State And That Of A Polar Molecules Chain In Noisy Environments

Quantum entanglement plays an important role in quantum communication and quantum computation. As a unique physical characteristics of quantum system, entanglement can not only verify the basic problem of quantum mechanics, but also act as an important resource for quantum information processing. It is found that entanglement is not the only type of quantum correlation useful for quantum information process, there are some quantum correlations called quantum discord which also offer some specific advantages for achieving tasks of quantum informationIn this thesis, we investigate the effects of noisy transmission channel and noisy encoding operations on the classical information capacity of dense coding by employing a Bell-class state as the entanglement resource. We find that the large amount of the shared entanglement does not always achieve the better information transmission capacity, and the maximal classical information capacity of dense coding can be obtained by adjusting the parameter of the channel resource under certain condition. Moreover, we also find that in the presence of noisy encoding operations, there exists a critical rotation rate below which dense coding will fail to attain an information transfer superior to classical communication, and infinite temperature environment is more harmful to implement the dense coding in contrast to zero temperature environment and dephasing environment.We also study the dynamics of the pairwise quantum discord (QD), classical correlation, and entanglement of formation for the three-qubit W-class state|W>123=1/2(|100>123+|010>123+(?)2|001>123) under the influence of various Markovian noises by analytically solving the master equation in the Lindblad form. Through numerical analysis, we find that entanglement of formation decreases asymptotically to zero with time for the dephasing noise, but it undergoes the sudden death for the bit-flip noise, the isotropic noise, as well as the zero temperature and infinite temperature environments. Moreover, QD diminishes to zero in an asymptotical way for all the investigated noises. Thus, when the W-class state|W>123is subject to the above Markovian noises, QD is more robust than entanglement of formation against decoherence excluding the phase-flip noise, implying that QD is more useful than entanglement to characterize the quantum correlation. We also find a remarkable character for the classical correlation in the presence of the phase-flip noise, i.e., classical correlation displays the behavior of sudden transition and then keeps constant permanently, but the corresponding QD just exhibits a very small sudden change. Besides, we verify the monogamic relation between the pairwise QD and entanglement of formation of the W-class state.Finally, pairwise QD, classical correlation and concurrence in the system of linear polar molecules arrays are investigated. It is found that QD, classical correlation and concurrence can be adjusted by varying the temperature as well as the ratio of the transition frequency to the dipole-dipole coupling constant.