强热辐射环境中两能级原子量子态保真度

两个两能级原子置于强热辐射场环境中，原子用泡利算符描述，环境用无穷的谐振子热库描述，运用密度矩阵方法，得到两能级原子密度矩阵元演化规律.针对三种不同的初始状态，分析置于热辐射场中原子量子态保真度.结果表明：当两个原子初始处于不同量子叠加态时，量子信息在传输过程中可能发生部分失真，也可能不失真. 关键词： 热辐射场 两能级原子 保真度 消相干     

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.     

Optical Bloch Equations Modified with Phonon-Induced Intensity-Dependent Dephasing

We extend the exciton population equations of a two-level quantum dot system with weak excitation to the ones with strong excitations, in which, the phonon-induced intensity-dependent dephasing time and decay rate are involved. The straightforward calculated populations from the modified population equations demonstrate the damping behavior of Rabi oscillation as the external field increasing. The effect of the intensity-dependent dephasing time and the intensity-dependent decay rate are also discussed.     

Quantum repeaters based on CNOT gate under decoherence

In this paper, we study single-qubit and single-user quantum repeaters based on CNOT gates under decoherence using the Kraus-operator representations of decoherence. We investigate the influence of decoherence on the information-disturbance trade-off of quantum repeaters. It is found that decoherence may lead to the appearance of three subspaces, called as the normal subspace, the anomalous subspace, and the decoherence-free subspace (DFS), respectively. It is indicated that in the normal subspace decoherence decreases the transmission and estimation fidelities, in the anomalous subspace decoherence enhances these fidelities, and in the DFS these fidelities do not change. The concept of the quality factor is introduced to evaluate the quality of the quantum repeater. It is indicated that the quality factor can be efficiently controlled and manipulated by changing the initial state of the probe qubit. It is found that under certain conditions the quantum repeater can be optimal even in the presence of decoherence.      

Intrinsic Decoherence on Two-Qubit Heisenberg XX Chain

Quantum teleportation is investigated by using the entangled states of two-qubit Heisenberg XX chain in an external uniform magnetic field as resources in the model of Milburn＇s intrinsic decoherence. Though intrinsic decoherence on quantum entanglement and quantum teleportation exerts different effects in different initial systems, proper magnetic fields and probabilities of different eigenstates in the initial states can weaken the effects.     

Influences of decoherence on the generation of a macroscopic superposition state using weak cross-Kerr effect

Considering a system in which a single photon and a coherent field propagate through a Kerr medium, when the weak cross-Kerr interaction between the coherent state and the single photon under decoherence is involved, this paper derives analytically a macroscopic superposition state by the superoperator method and investigates the influences of decoherence on the coherence properties of the obtained state. It finds that the macroscopic superposition state will experience evolution from a pure superposltion state to a mixed state in a dissipative environment and the Kerr effect makes the field display a periodic revival from decoherence for a short time.     

Solving the Measurement Problem: De Broglie--Bohm Loses Out to Everett

The quantum theory of de Broglie and Bohm solves the measurement problem, but the hypothetical corpuscles play no role in the argument. The solution finds a more natural home in the Everett interpretation.     

Classical Behavior After a Phase Transition: I. Classical Order Parameters

We analyze the onset of classical field configurations after a phase transition. Firstly, we motivate the problem by means of a toy model in quantum mechanics. Subsequently, we consider a scalar field theory in which the system-field interacts with its environment, represented both by further scalar fields and by its own short-wavelength modes. We show that for very rapid quenches, the order parameter can be treated classically by the time taken for it to achieve its ground state values (spinodal time).     

A Generalized Bell Inequality and Decoherence for the K0KO

First, a generalized Bell inequality for different times and for different quasi-spin states is developed. We focus on special quasi-spin eigenstates and times. The inequality based on a local realistic theory is violated by the CP-violating parameter [1] if the quantum theory is used to recalculate the probabilities. Next, the quantum mechanical probabilities are modified by the decoherence approach, which enables the initial state to factorize spontaneously. In this way we get a lower limit for the decoherence parameter , which measures the degree of decoherence. This result is compared with the experimental value [2, 3] of the decoherence parameter deduced from the data of the CPLEAR experiment [4].