Understanding and Controlling Open Quantum Dynamics

Abstract

In this thesis, we examine the dynamics of open quantum systems, that is, systems interacting with an external environment. Due to this interaction, such systems are generally subject to decoherence. To combat decoherence, we construct continuous fields that provide universal protection of two-qubit states and two-qubit gates. We also consider decoherence control in spin squeezing. In particular, we construct control fields that serve a dual purpose: they protect the system against decoherence, and, at the same time, effectively transform the squeezing Hamiltonian such that better squeezing performance is obtained. Moving on, we look at the effect of initial correlations in large multiparticle systems. We show that the effect of the initial correlations can be amplified as the number of particles is increased using both exactly and non-exactly solvable models. Moreover, we emphasize the non-trivial role played by the state preparation procedure in open quantum systems. Finally, we examine decoherence due to the system?s interaction with a composite environment.