Measure Of Quantum Entanglement Of Two-Body And Nonclassicality

Quantum entanglement and nonclassicality play an important role in understanding the fundamentals of quantum physics, and to measure them is an important aspect of the research of quantum entanglement and nonclassicality. With the deepening of understanding, we can now properly measure the quantum entanglement of two-body. Many measures have been proposed, such as partial entropy, concurrence, and negativity. However, we still lack an effective measure to describe the entanglement of there-body and multi-body. Moreover, the finding of entanglement sudden death forces us to make a deeper understanding of current measures of entanglement, such as concurrence and negativity. As for the measures of nonclassicality, from early Mandle Q-factor, to nonclassical distance, to nonclassical depth, then the newly proposed entanglement potential, the description of nonclassicality goes through a course from one-sided, inaccurate, poorly operational, towards a comprehensive, accurate and easy-operation. However, even so, we still have no single indicator that can reflect all of the nonclassical behaviors. Based on the above, a further in-depth study of the measure of quantum entanglement and nonclassicality is also needed.In this thesis, we introduce several measures of quantum entanglement and nonclassicality, such as two-body entanglement measures, partial entropy, concurrence, and negativity, and nonclassicality measures, the negativity of the Wigner function and entanglement potential. Furthermore, we study and compare these measures in concrete physical processes. We investigate the entanglement dynamics of two Tavis-Cummings atoms interacting with different cavity fields by using the concurrence and the negativity, and we find that the negativity is always less than or equal to the concurrence for two-qubit systems. We also investigate the nonclassicality for Fock states and Schrodinger cat states in a decoherence process by exploiting the entanglement potential and the negativity of the Wigner function. It is found that the negativity of the Wigner function is wiped out for losses more than 50% while the entanglement potential is always positive, and the negativity of the Wigner function is much more sensitive to the extra losses than that of the entanglement potential. Besides, we still study the Wigner function of arbitrary quantum state in linear loss process, and give a "bound condition". The Wigner functions of all the states satisfying this bound condition will lose its negative distribution when the losses exceed 50%.