Generation and Suppression of Decoherence in Artificial Environment for Qubit System

Abstract

A quantum system with finite degrees of freedom can simulate a composite of a system and its environment if the state of the hypothetical environment is randomized by external manipulation. We propose to examine various techniques in quantum information processing in virtual noisy environment with two concrete examples. One simulates phase decoherence of a single qubit in a transmission line, and the other does in a quantum memory. In both cases, the bang-bang control, a typical example of useful techniques employed in quantum information processing, is observed to be effective to suppress decoherence.

Realization of controllable open system with NMR

“…We illustrate our idea to obtain various open systems or to engineer the environment in figure 1 [21,22,26,27], see also [23,24]. If a well-defined quantum system (such as a qubit) shows an exponential relaxation, the system interacts with a surrounding short-time memory (or, Markovian) environment.…”

“…We have been realizing an engineered environment and studying methods protecting a system from environment [21,26,27]. Our engineered environment may be regarded as a realization of the pseudomode [23,24] or the extended collision model [25].…”

Using the quantum Zeno effect for suppression of decoherence

“…The correlation time is of the order of J 2p , usually of few milliseconds for a carbon and hydrogen nuclei combination and thus this interaction is well controllable with NMR techniques. A similar approach has been reported, but using a series of pulses instead of magnetic impurities [19].…”

“…In order to understand the essence of QZE, it is sufficient to consider a coherent superposition of a qubit being dephased by a randomly fluctuating classical field [1,2], with the concept of 'mixing process' [19]. The relevant Hamiltonian is thus…”

“…C spin during the QZE experiment is performed as follows. The pulse sequence of equation(19) is divided into…”