Gravitationally Induced Decoherence in Macroscopic Systems

A quantum master equation for the time evolution of the center of mass (CM) of a macroscopic body is derived which takes into account the influence of the system's gravitational field over the CM wave function. As a consequence, all the relevant phenomenological features of the so-called GRW (Ghirardi, Rimini, and Weber) model are reproduced with no free parameters. The model presented here predicts also the existence of a transition region for the mass of the system—a kind of frontier between quantum (coherent) and classical (decoherent) behavior.     

腔场初始态对两量子比特空间退相干的影响

研究了两个二能级原子与一个单模腔场的相互作用中,腔场的不同初始态对原子间相对位置退相干的影响。从描述原子间相对位置状态的约化密度矩阵出发,假设原子间相对位置为两个高斯波包的叠加态,讨论了当腔场初始态分别为热态、Fock态和压缩态情况下,原子与光场的相互作用对两原子间相对位置相干性的影响。发现腔场的初始态不同,原子间相对位置的退相干情况有所不同。当腔场初始态为热态或Fock态时,原子间相对位置的相干性会周期性的衰减和回复,而当腔场初始态为压缩态时,原子间相对位置会出现部分退相干,且退相干程度与原子间相对位置的大小成余弦变化关系。     

Effect of Decoherence Induced by a Spin Environment on Quantum Channel Capacity

We investigate the effect of decoherence from a spin environment on the quantum channel capacity.Our results imply that the time evolution of the quantum channel capacity depends on the number of freedom degrees of the environment,the tunneling element,the initial state of the environment,and the system-environment coupling strength.From the analysis,we find that the strong tunneling elements and the weak coupling strength can enhance the quantum channel capacity while the environment with a large number of freedom degrees and the strong coupling strength will shrink it.     

Normal Ordering Solution to Quantum Dissipation and Its Induced Decoherence

We implement the normal ordering technique to study the quantum dissipation of a single mode harmonic oscillator system. The dynamic evolution of the system is investigated for a reasonable initial state by solving the Schrödinger equation directly through the normal ordering technique. The decoherence process of the system for the cases T=0 K and T≠0 K is investigated as an application.     

Quantum Decoherence of Macroscopic Object Induced by Inner Environments: an Exactly Solvable Model

We revisit the quantum decoherence problem of the center of mass motion of a macroscopic object,which is modelled as a one-dimensional atom chain.Induced by the coupling of the center of mass (C.M) motion with the inner degrees of freedom,this inner-environment-induced decoherence is reflected by the localization of the C.M wave packet.We show that,the C.M motion is coupled to the inner states only when the chain has interaction with the external potential.This result provides a realistic mechanism for the analysis of the inner-environment-induced localization of a macroscopic object.     

Dynamics of Optically Driven Exciton and Quantum Decoherence

By using the normal ordering method, we study the state evolution of an optically driven excitons in aquantum well immersed in a leaky cavity, which was introduced by Yu-Xi Liu et al. [Phys. Rev. A63 (2001) 033816]. Theinfluence of the externallaser field on the quantum decoherence of a mesoscopically superposed state of the excitons isinvestigated. Our result shows that, the classical field can compensate the energy dissipation of the excitons. Althoughthe decoherence rate of the excitonic Schrodinger cat state does not depend on the external field, the phase of thedecoherence factor can be well controlled by adjusting the amplitude of the external field as well as the detuning betweenthe field and the transition frequency of the atom.     

混沌微扰导致的量子退相干

研究了无限深势阱内两个粒子的耦合导致的量子退相干和量子行为趋近于经典混沌运动的过程．当一个粒子的质量减小时,它对另外一个粒子经典混沌扩散的影响逐渐减小．强混沌机理使得轻粒子的作用类似于噪声,从而有效得抑制另外一个粒子的量子相干性．轻粒子的退相干效应随着有效普朗克常数的减小逐渐增强．在这个过程中,另外一个粒子的量子扩散从动力学局域化行为逐渐过渡到经典极限．当有效普朗克常数足够小时。它的量子扩散与经典混沌扩散相符合．该粒子的线性墒随时间演化迅速趋近于饱和值,并且饱和值随着有效普朗克常数减小以指数函数形式从零趋近于l.     

Algebraic Formulation of Quantum Decoherence

An algebraic formalism for quantum decoherence in systems with continuous evolution spectrum is introduced. A certain subalgebra, dense in the characteristic algebra of the system, is defined in such a way that Riemann–Lebesgue theorem can be used to explain decoherence in a well defined final pointer basis.     

Brun-Type Formalism for Decoherence in Two-Dimensional Quantum Walks

We study decoherence in the quantum walk on the xy-plane.We generalize the method of decoherent coin quantum walk,introduced by [T.A.Brun,et al.,Phys.Rev.A 67(2003) 032304],which could be applicable to all sorts of decoherence in two-dimensional quantum walks,irrespective of the unitary transformation governing the walk.As an application we study decoherence in the presence of broken line noise in which the quantum walk is governed by the two-dimensional Hadamard operator.     

Influence of Intrinsic Decoherence on Entanglement in Two-Qubit Quantum Heisenberg XYZ Chain

Taking the intrinsic decoherence effect into account, we investigate the time evolution of entanglement for two-qubit XYZ Heisenberg model in an external uniform magnetic field. Concurrence, the measurement of entanglement,is calculated. We show how the intrinsic decoherence modifies the time evolution of the entanglement and find that at short-time case, concurrence is oscillating as increasing magnetic field, which implies that entanglement may be enhanced or weakened in some time regions.     

Influence of Intrinsic Decoherence on Entanglement in Two-Qubit Quantum Heisenberg XYZ Chain

Taking the intrinsic decoherence effect into account, we investigate the time evolution of entanglement for two-qubit XYZ Heisenberg model in an external uniform magnetic field. Concurrence, the measurement of entanglement,is calculated. We show how the intrinsic decoherence modifies the time evolution of the entanglement and find that at short-time case, concurrence is oscillating as increasing magnetic field, which implies that entanglement may be enhanced or weakened in some time regions.     

消干效应和量子力学新解释的意义

简单介绍了消干 (decoherence)效应以及量子力学的一种新解释———由Griffiths,Gell Mann和Omn埁ｓ等独立提出的“消干历史解释”的由来和要点 ,评述了这一进展在量子理论发展中的意义 .     

General Decoherence Suppression in Three-Level Atom in V- and Ξ-Configurations

In this paper, we present the decoupling bang-bang （BB） twin-born pulses to suppress the genera/deco- herence, both amplitude and phase decoherence, in a three-level atom in V- and Ξ-configurations. We give the exact sequence of periodic twinborn pulses in such systems.     

Entanglement Evolution of Three-Qubit States under Local Decoherence

By using negativity as entanglement measure, we have investigated the effect of local decoherence from a non-Markovian environment on the time evolution of entanglement of three-qubit states including the GHZ state, the W state, and the Werner state. From the results, we find that the entanglement dynamics depends not only on the coupling strengths but also on the specific states of concern. Specifically, the entanglement takes different behaviors under weak or strong coupling and it varies with the quantum states under study. The entanglement of the GHZ state and the Werner state can be destroyed completely by the local decoherence, while the entanglement of the W state can survive through the local decoherence partially.     

Protecting Distribution Entanglement by Weak Measurement and Reversal under Various Decoherence Sources

Protection of entanglement from disturbance of the environment is an essential task marion processing. We examine the validity and limitation of the weak measurement and reversal in quantum infor- （WMR） operation in the protection of distributed entanglement from various decoherence sources. Since the entanglement variation can be investigated analytically for an arbitrarily entangled bipartite pure state under three kinds of typical noisy quantum channels, we show explicitly that the WMR operation indeed helps for protecting distributed entanglement from ampli- tude damping and phase damping, but not for depolarizing. Bxperimental feasibility for testing our results is discussed using current laboratory techniques.     

Entropy Squeezing in Coupled Field-Superconducting Charge Qubit with Intrinsic Decoherence

We investigate the entropy squeezing in the system of a superconducting charge qubit coupled to a single mode field. We find an exact solution of the Milburn equation for the system and discuss the influence of intrinsic decoherence on entropy squeezing. As a comparison, we also consider the variance squeezing. Our results show that in the absence of the intrinsic decoherence both entropy and variance squeezings have the same periodic properties of time,and occur at the same range of time. However, when the intrinsic decoherence is considered, we find that as the time going on the entropy squeezing disappears fast than the variance squeezing, there exists a range of time where entropy squeezing can occur but variance squeezing cannot.     

Entanglement Evolution of Three-Qubit States under Local Decoherence

By using negativity as entanglement measure, we have investigated the effect of local decoherence from a non-Markovian environmenton the time evolution of entanglement of three-qubit states including the GHZ state, the W state, and the Werner state. From the results, we find that the entanglement dynamics depends not only on the coupling strengths but also on the specific states of concern. Specifically, the entanglement takes different behaviors under weak or strong coupling and it varies with the quantum states under study. The entanglement of the GHZ state and the Werner state can be destroyed completely by the local decoherence, while the entanglement of the W state can survive through the local decoherence partially.     

Decoherence in solid-state qubits

The interaction of solid-state qubits with environmental degrees of freedom strongly affects the qubit dynamics, and leads to decoherence. In quantum information processing with solid-state qubits, decoherence significantly limits the performances of such devices. Therefore, it is necessary to fully understand the mechanisms that lead to decoherence. In this review, we discuss how decoherence affects two of the most successful realizations of solid-state qubits, namely, spin qubits and superconducting qubits. In the former, the qubit is encoded in the spin 1/2 of the electron, and it is implemented by confining the electron spin in a semiconductor quantum dot. Superconducting devices show quantum behaviour at low temperatures, and the qubit is encoded in the two lowest energy levels of a superconducting circuit. The electron spin in a quantum dot has two main decoherence channels, a (Markovian) phonon-assisted relaxation channel, due to the presence of a spin–orbit interaction, and a (non-Markovian) spin bath constituted by the spins of the nuclei in the quantum dot that interact with the electron spin via the hyperfine interaction. In a superconducting qubit, decoherence takes place as a result of fluctuations in the control parameters, such as bias currents, applied flux and bias voltages, and via losses in the dissipative circuit elements.