Characterization And Decoherence Control Of Open Quantum Systems

Download or read book Characterization and Decoherence Control of Open Quantum Systems written by Masoud Mohseni and published by . This book was released on 2007 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: An optimal quantum algorithm for "direct characterization of quantum dynamics" (DCQD) is introduced. The DCQD method can be utilized to completely determine the quantum dynamical superoperator acting on an open quantum system. In contrast to all other known quantum process tomography (QPT) schemes, this scheme relies on error-detection techniques and does not require any quantum state tomography. By analysis of the number of required experimental configurations and quantum operations in a given Hilbert space, it is demonstrated that this approach is more efficient than all other known QPT schemes. DCQD can be applied, by construction, to the task of partial characterization of quantum dynamics. Specifically, it is demonstrated that the DCQD algorithm can be efficiently used for Hamiltonian identification, and also for simultaneous determination of both the relaxation time T1 and dephasing time T2. Furthermore, it is argued that the DCQD scheme is experimentally implementable in a variety of prominent quantum information processing systems, and it is explicitly shown how it can be physically realized in photonic systems with present day technology. The ability of a quantum system to perform arbitrary or "universal" quantum operations is restricted to its naturally available/controllable interactions. It is shown that quantum systems with an effective exchange interaction can be made operationally universal by utilizing a subspace or a subsystem of the combined principal system and an auxiliary system. Moreover, it is demonstrated that universal fault-tolerant quantum computation can be performed on these systems without utilizing any form of single-qubit control. Characterization and control of open quantum systems are among the central and fundamental problems in quantum physics. A crucial primitive is the characterization of the dynamics of a quantum system that has an unknown interaction with its embedding environment. Another essential task is to control the decoherence of an open quantum system by using naturally available interactions. This thesis addresses the above fundamental problems in two separate parts. In the first part, a general theory for direct and complete characterization of quantum dynamics is introduced. In the second part, a scheme for performing arbitrary quantum operations on spin-based quantum systems is presented. This scheme can be implemented in the presence of environmental noise and faulty quantum operations without need to control the state of spins individually.