Quantum control of entanglement by phase manipulation
by
Vladimir S. Malinovsky
Michigan Center for Theoretical Physics & FOCUS Center, Department of Physics, University of Michigan, Ann Arbor, MI 48109
Coauthors: Ignacio R. Sola, Departamento de Quimica Fisica I, Universidad Complutense, 28040 Madrid, Spain

A new method of entangled states preparation of two-qubit systems is proposed. The method combines the techniques of coherent control by manipulation of the relative phase between pulses, and adiabatic control using time-delayed pulse sequences. A two-qubits system with couplings forming a closed-loop configuration allows full preparation of entangled states by controlling the relative phase of the fields. We have shown that time-delayed sequences provide very stable mechanisms to control the dynamics in the adiabatic regime. The relative phase between the pulses is essential in preparing entanglement with specific phase relationships. We have obtained the exact relationship between the control phase and the phase of the prepared entangled state. Both counterintuitive and intuitive pulse sequences are needed to prepare entanglement with all possible phases. In the resonant scheme we have shown that the relative phase between the pulses is the most sensitive parameter that governs the entanglement in the counterintuitive sequence, while the pulse area is the most sensitive parameter that controls entanglement in the intuitive sequence. The off-resonant scheme provides the most stable mechanism to prepare specific entangled states. We believe that the present scheme provides additional flexibility for quantum control of entanglement and could facilitate experimental implementation of quantum logic gates in a few qubits systems.

Date received: March 15, 2004