Generation and control of quantum entanglement in physical systems

Abstract

This thesis will discuss four topics in the field of generation and control of quantum entanglement in physical systems.

The first topic discusses the maximal entanglement generation in a spin chain of XX model with specially engineered couplings. A universal solution is found for an odd-numbered spin chain by introducing asymmetry in the optimal perfect-state-transfer solution. The introduction of asymmetric couplings is analogous to an insertion of a beam splitter.

The second topic discusses the realization of the multiparticle Hanbury Brown-Twiss interferometer in a spin network. For an N-particle system, the interference effect is manifested only in the normal ordered Nth-order intensity correlation function. This effect is enhanced through a post-selection process in which the multipartite Greenberger-Horne-Zeilinger entanglement is generated. An experimental realization through Nitrogen-Vacancy color centers in diamond crystals is proposed.

The third topic studies the coherent control of the steady-state entanglement in lossy and driven coupled atom-cavity systems. It is found that the steady-state entanglement can be coherently controlled through the tuning of the phase difference between the driving fields. The controlling process is reminiscent of the coherent trapping of the three-level atoms using two classical coherent fields.

The fourth topic studies the thermalization of a single atom-cavity system by examining the relation between the steady state and a thermal equilibrium state of the system when the parameters such as the reservoir temperature and the driving strength are varied. It is found that quantum discord appears to be a suitable quantity to characterize the degree of thermalization.