From Open Quantum Systems to Open Quantum Maps

For a class of quantized open chaotic systems satisfying a natural dynamical assumption we show that the study of the resolvent, and hence of scattering and resonances, can be reduced to the study of a family of open quantum maps, that is of finite dimensional operators obtained by quantizing the Poincaré map associated with the flow near the set of trapped trajectories.     

Initial Decoherence of Open Quantum Systems

We present a new short-time approximation scheme for evaluation of decoherence. At low temperatures, the approximation is argued to apply at intermediate times as well. It then provides a tractable approach complementary to Markovian-type approximations, and appropriate for evaluation of deviations from pure states in quantum computing models.     

Classical Properties of Infinite Quantum Open Systems

Long time asymptotic properties of a class of environmentally induced dynamical semigroups on arbitrary von Neumann algebras are discussed. Such a semigroup selects observables, called effective observables, which are immune to the process of decoherence and so evolve in a reversible automorphic way. In particular, it is shown that effective observables of the quantum system in the thermodynamic limit, subjected to a specific interaction with another quantum system, obey classical dynamics.This work was supported by the KBN research grant no 5P03B 081 21     

Controllable Subspaces of Open Quantum Dynamical Systems

This paper discusses the concept of controllable subspace for open quantum dynamical systems. It is constructively demonstrated that combining structural features of decoherence-free subspaces with the ability to perform open-loop coherent control on open quantum systems will allow decoherence-free subspaces to be controllable. This is in contrast to the observation that open quantum dynamical systems are not open-loop controllable. To a certain extent, this paper gives an alternative control theoretical interpretation on why decoherence-free subspaces can be useful for quantum computation.     

Dynamics of Multi-Level Open Quantum Systems with Initial System-Environment Correlations

Physics of Particles and Nuclei Letters - Exact and approximate master equations were derived by the projection operator method for the reduced statistical operator of a multi-level open quantum...     

Scattering Theory for Open Quantum Systems with Finite Rank Coupling

Quantum systems which interact with their environment are often modeled by maximal dissipative operators or so-called Pseudo-Hamiltonians. In this paper the scattering theory for such open systems is considered. First it is assumed that a single maximal dissipative operator A _D in a Hilbert space \({\mathfrak H}\) is used to describe an open quantum system. In this case the minimal self-adjoint dilation \(\widetilde K\) of A _D can be regarded as the Hamiltonian of a closed system which contains the open system \(\{A_{\!D},{\mathfrak H}\}\), but since \(\widetilde K\) is necessarily not semibounded from below, this model is difficult to interpret from a physical point of view. In the second part of the paper an open quantum system is modeled with a family {A(μ)} of maximal dissipative operators depending on energy μ, and it is shown that the open system can be embedded into a closed system where the Hamiltonian is semibounded. Surprisingly it turns out that the corresponding scattering matrix can be completely recovered from scattering matrices of single pseudo-Hamiltonians as in the first part of the paper. The general results are applied to a class of Sturm–Liouville operators arising in dissipative and quantum transmitting Schrödinger–Poisson systems.     

Variational Quantum Algorithms for the Steady States of Open Quantum Systems

The solutions of the problems related to open quantum systems have attracted considerable interest.We propose a variational quantum algorithm to find the steady state of open quantum systems.In this algorithm,we employ parameterized quantum circuits to prepare the purification of the steady state and define the cost function based on the Lindblad master equation,which can be efficiently evaluated with quantum circuits.We then optimize the parameters of the quantum circuit to find the steady state.Numerical simulations are performed on the one-dimensional transverse field Ising model with dissipative channels.The result shows that the fidelity between the optimal mixed state and the true steady state is over 99%.This algorithm is derived from the natural idea of expressing mixed states with purification and it provides a reference for the study of open quantum systems.     

Perturbation Theory for Open Two-Level Nonlinear Quantum Systems

Perturbation theory is an important tool in quantum mechanics. In this paper, we extend the traditional perturbation theory to open nonlinear two-level systems, treating decoherence parameterγ as a perturbation. By this virtue, we give a perturbative solution to the master equation, which describes a nonlinear open quantum system. The results show that for small decoherence rateγ, the ratio of the nonlinear rate C to the tunneling coefficient V (i.e., r=C/V) determines the validity of the perturbation theory. For small ratio r, the perturbation theory is valid, otherwise it yields wrong results.     

Robust Set Stabilization and Its Instances for Open Quantum Systems

We propose and discuss a novel concept of robust set stabilization by permissible controls; this concept is helpful when dealing with both a priori information of model parameters and different permissible controls including quantum measurements. Both controllability and stabilization can be regarded as the special case of the novel concept. An instance is presented for a kind of uncertain open quantum systems to further justify this generalized concept. It is underlined that a new type of hybrid control based on periodically perturbed projective measurements can be the permissible control of uncertain open quantum systems when perturbed projective measurements are available. The sufficient conditions are given for the robust set stabilization of uncertain quantum open systems by the hybrid control, and the design of the hybrid control is reduced to selecting the period of measurements.     

Time Relativity in the Dynamics of Open Quantum Systems

Various methods for determining the Coulomb logarithm in the kinetic theory of transport and various variants of the choice of the plasma screening constant, taking into account and disregarding the contribution of the ion component and the boundary value of the electron wavevector are considered. The correlation of ions is taken into account using the Ornstein–Zernike integral equation in the hypernetted-chain approximation. It is found that the effect of ion correlation in a nondegenerate plasma is weak, while in a degenerate plasma, this effect must be taken into account when screening is determined by the electron component alone. The calculated values of the electrical conductivity of a hydrogen plasma are compared with the values determined experimentally in the megabar pressure range. It is shown that the values of the Coulomb logarithm can indeed be smaller than unity. Special experiments are proposed for a more exact determination of the Coulomb logarithm in a magnetic field for extremely high pressures, for which electron scattering by ions prevails.     

Linear Response Theory for Thermally Driven Quantum Open Systems

This note is a continuation of our recent paper [V. Jakšić Y. Ogata, and C.-A. Pillet, The Green-Kubo formula and Onsager reciprocity relations in quantum statistical mechanics. Commun. Math. Phys. in press.] where we have proven the Green-Kubo formula and the Onsager reciprocity relations for heat fluxes in thermally driven quantum open systems. In this note we extend the derivation of the Green-Kubo formula to heat and charge fluxes and discuss some other generalizations of the model and results of [V. Jakšić Y. Ogata and C.-A. Pillet, The Green-Kubo formula and Onsager reciprocity relations in quantum statistical mechanics. Commun. Math. Phys. in press.].     

Probability Representation of Kinetic Equations for Open Quantum Systems

The tomographic probability distribution is used to describe the kinetic equations for open quantum systems. Damped oscillator is studied. The purity parameter evolution for different damping regimes is considered.     

A Closed-System Approach to Quantum Retrodiction in Open Systems

Ban (Int. J. Theor. Phys. 46:184, 2007) has shown how retrodictive open systems evolution may be treated as unitary using non-equilibrium thermo field dynamics. Here we describe the application of another technique with the same purpose, Fano diagonalisation.     

Erratum to: Quantum Statistical Effects in Nuclear Reactions,Fission, and Open Quantum Systems

Since the authors did not see the proofs before the paper was published, the presented corrections should be taken into account when one reads the paper.     

On the Nature of Fermi Golden Rule for Open Quantum Systems

We consider a general class of models consisting of a small quantum system $S$ interacting with a reservoir $R$ . We compare three applications of 2nd order perturbation theory (the Fermi Golden Rule) to the study of such models: (1) the van Hove (weak coupling) limit for the dynamics reduced to $S$ ; (2) the Fermi Golden Rule applied to the Liouvillean—an argument that was used in recent papers on the return to equilibrium; (3) the Fermi Golden Rule applied to the so-called C-Liouvillean. These three applications lead to three Level Shift Operators. As our main result, we prove that if the reservoir $R$ is thermal (if it satisfies the KMS condition), then the Level Shift Operator obtained in (1) (often called the Davies generator) and the Level Shift Operator constructed in (2) are connected by a similarity transformation. We also show that the Davies generator coincides with the Level Shift Operator obtained in (3) for a general $R$ .     

带有锥形增益区14xxnm量子阱激光器的研制

利用MOCVD生长了14xxnm AlGaInAs/AlInAs/InP应变量子阱外延片.采用带有锥形增益区脊型波导结构和普通条形脊型波导结构在相同的实验条件下制作800 μm腔长激光器管芯,在相同的驱动电流下前者可以获得更高的输出光功率,而且P-Ⅰ曲线线性度较好、饱和电流高. 1200 μm腔长带有锥形增益区脊型波导结构管芯功率达到500 mW,饱和电流3 A以上,峰值波长1460 nm,远场发散角为39°×11°.     

Algebraic Method in the Analysis of Decoherence-Free Subspaces in Open Quantum Systems

In open quantum systems, a subspace which is not affected by the environmental noise is called a decoherence-free subspace. Such a subspace plays an important role in applications such as quantum information transmissions. In the literature, several “definitions” of decoherence-free subspaces were proposed, but they are model-dependent and slightly different. In this paper, we will study a general framework of decoherence-free subspaces and provide a criterion for the existence of a decoherence-free subspace in open quantum systems.     

一维周期性增益介质的临界长度

用传输矩阵方法研究了一维周期性增益介质的透射频谱随系统层数的变化规律.研究发现：对层数一定的介质,透射率在某些频率上有很大的峰值;增加层数,尖峰在频谱图上出现的位置会发生移动,且对不同的频段,其位置随介质层数的变化规律是不同的.考察了这种系统中每个频率的光所对应的临界长度,解释了不同频段激光出现位置随层数变化的规律.比较了周期系统和随机系统中临界长度与频率关系的异同,用群速度理论和能带理论对此做了解释.