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Acta Physica Sinica

SUPPRESSION OF DECOHERENCE IN TWO STATE QUANTUM SYSTEMS INTERACTING WITH BATH THROUGH AN EXTERNAL CONTROLLABLE FIELD

Hao Sheng

Published Jan 1, 2000• 0 citations
OpenAlex

Abstract

In this paper, the problem of the decoherence of two\|state quantum systems interacting with a bath through an external controllable driving field is discussed. The time evolution of the off-diagonal elements of the density operator in two\|state quantum systems is obtained. The relation between the decoherence and the external controllable driving field is also obtained. Thus we establish the restriction equation that must be satisfied by the external controllable driving field when the decoherence is to vanish.

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In this paper, the problem of the decoherence of two|state quantum systems interacting with a bath through an external controllable driving field is discussed. The time evolution of the off-diagonal elements of the density operator in two|state quantum systems is obtained. The relation between the decoherence and the external controllable driving field is also obtained. Thus we establish the restriction equation that must be satisfied by the external controllable driving field when the decoherence is to vanish.
The problem of decoherence of two-state quantum systems interacting with a bath through an external controllable driving field without rotating wave approximation is discussed.The off-diagonal elements of density operator in two-state quantum systems are obtained.The result reflects that decoherence of the two-state quantum systems has something to do with its original state,frequency of the bath and external controllable driving field.The relation between the decoherence and external controllable driving field is studied.Properties of an external controllable driving field are obtained when the two-state quantum systems of coherence is maintained.
The elimination of decoherence of a multiphoton two-state quantum system by using an appropriate external driving field is considered. The multiphoton process caused by the noise field has a supersymmetric Lie algebraic structure. The time-evolution equations for the off-diagonal elements of the density operator of the two-state system are derived in the interaction picture. A simple explicit formula is given for the time-dependent external driving field used to eliminate the decoherence of the multiphoton two-state system.
The elimination of decoherence of two-state quantum systems interacting with a thermal reservoir through an external controllable driving field is discussed in the present paper. The restriction equation with which the external controllable driving field should agree will be derived. Based on this, we obtain the time-development equation of the off-diagonal elements of density operator in the supersymmetric multiphoton two-state quantum systems, which is helpful for studying the polarization evolution in this two-state quantum model.
A general theory is presented for the treatment of decoherence of a multilevel quantum system (with many degrees of freedom) interacting with multi-bath reservoir and driven by ac fields. In this approach, the system is described by a reduced density operator and the multi-bath reservoir is characterized by a number of spectral densities. The reduced density operator is governed by the master equation in which the effect of ac driving fields and the leakage to non-computational states are included. The theory is applied to the study of decoherence of a two-dimensional (2D) SQUID flux qubit coupled to control and readout circuits. The predicted results are in very good agreement with available experimental results in the absence of driving fields and with the analytic results of a dissipative two-level system in the presence of weak driving fields. The relaxation and decoherence times versus the parameters and temperature of the control and readout circuits are also explored in details to facilitate the optimization of the 2D SQUID qubit.
A molecular system in contact with a bath undergoes strong decoherence processes. We examine a control scheme to minimize dissipation, while maximally retaining coherent evolution, by relating the evolution of the molecule to that of an identical freely propagating system. We seek a driving field that maximizes the projection of the open molecular system onto the freely propagated one. The evolution in time of a molecular system consisting of two nonadiabatically coupled electronic states interacting with a bath is followed. The driving control field that overcomes the decoherence is calculated. A proposition to implement the scheme in the laboratory using feedback control is suggested.
We present an approach that allows quantifying decoherence processes in an open quantum system subject to external time-dependent control. Interactions with the environment are modeled by a standard bosonic heat bath. We develop two unitarity-preserving approximation schemes to calculate the reduced density matrix. One of the approximations relies on a short-time factorization of the evolution operator, while the other utilizes expansion in terms of the system-bath coupling strength. Applications are reported for two illustrative systems: an exactly solvable adiabatic model, and a model of a rotating-wave quantum-computing gate function. The approximations are found to produce consistent results at short and intermediate times.