Qubitlerin kuantum kontrolü: Zaman sıralaması etkileri

In this thesis, I have studied five different problems concerning the qubits and the dynamics of entanglement between the qubits under various conditions. First, the exact analytical dynamics of entanglement between two qubits subject to independent kicks and Gaussian pulses as an external magnetic field lie along z-axes or x-y plane has been investigated. I have showed that "almost-steady" high entanglement can be created between two initially unentangled qubits by using carefully designed kick or pulse sequences.The dynamics of several quantum correlation measures for a three qubit sytem subject to independent noise in their energy levels has been investigated to understand the life time of quantum correlations for system in contact with an environment. Along these lines, I have compared the dynamics of quantum discord, entanglement and Bell-nonlocalities under the same conditions for three qubits that have stochastic energy levels represented as classical Ornstein-Uhlenbeck noise. I have showed that Bell-nonlocalities as well as bipartite entanglement have life times shorter than the tripartite entanglement, while the quantum discord is immune to sudden death independent of the non-Markovianity of the dynamics and the purity of the initial states. Furthermore, I have concluded that the non-Markovianity of the dynamics only prolongs the death of quantum correlations, except, quantum discord which does not suffer sudden death.I have also analyzed the entanglement dynamics of two and three qubits which interact with each other by dipole-dipole interaction. I have assumed each qubit is embedded in its own non-Markovian environment and connected to each other by dipole-dipole interactions through next-nearest, J_1, and next-next-nearest, J_2, couplings. I have showed that the entanglement created by the dipole-dipole interaction is damped to zero by the qubit-environment interactions. Moreover, in the region where J_2/J_1<0, the full disentanglement time takes longer compared to the region where J_2/J_1>0.