用改进的量子分子动力学研究中能重离子碰撞中多重碎裂

本文利用改进的量子分子动力学模型(MQMD)研究中能重离子碰撞中的多重碎裂过程.在MQMD的基础上通过模拟计算发现:MQMD由于考虑了动量相关势和Pauli势,极大地改善了多重碎裂产额的计算结果与实验数据的比较.同时研究了二者对碰撞动力学的不同影响.最后,讨论了理论计算与实验结果仍有矛盾的原因,并提出了进一步改进的方案.     

Isentropic Compression of Deuterium by Quantum Molecular Dynamics

In this work we present our calculations of the compression isentrope of deuterium. We use an ab initio molecular dynamics approach to compute pressure and internal energy of dense deuterium in the range of temperatures 293–25000 K and densities 0.9–4.3 g/cm³. We then restore the isentrope and compare the results with experimental data and other theories. The position of the calculated isentrope slightly depends on the initial point and agrees with the low‐pressure part and the highest‐pressure point of the measurements. However, we do not observe the density jump registered experimentally at P ≈ 130 GPa (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Emergent Measure-Dependent Probabilities from Modified Quantum Dynamics Without State-Vector Reduction

Counting outcomes is the obvious algorithm for generating probabilities in quantum mechanics without state-vector reduction (i.e., many-worlds). This procedure has usually been rejected because for purely linear dynamics it gives results in disagreement with experiment. Here it is shown that if non-linear decoherence effects (previously proposed by other authors) are combined with an exponential time dependence of the scale for the non-linear effects, the correct measure-dependent probabilities can emerge via outcome counting, without the addition of any stochastic fields or metaphysical hypotheses.     

Memory Effects in Quantum Dynamics Modelled by Quantum Renewal Processes

Simple, controllable models play an important role in learning how to manipulate and control quantum resources. We focus here on quantum non-Markovianity and model the evolution of open quantum systems by quantum renewal processes. This class of quantum dynamics provides us with a phenomenological approach to characterise dynamics with a variety of non-Markovian behaviours, here described in terms of the trace distance between two reduced states. By adopting a trajectory picture for the open quantum system evolution, we analyse how non-Markovianity is influenced by the constituents defining the quantum renewal process, namely the time-continuous part of the dynamics, the type of jumps and the waiting time distributions. We focus not only on the mere value of the non-Markovianity measure, but also on how different features of the trace distance evolution are altered, including times and number of revivals.     

Quantum Trajectory Approach to Molecular Dynamics Simulation with Surface Hopping

In this work we propose a quantum trajectory approach to the powerful molecular dynamics simulation with surface hopping, from an insight that an effective “observation” is actually implied in the simulation through tracking the forces experienced, just like checking the meter's result in quantum measurement process. This treatment can build the nonadiabatic surface hopping on a physical foundation, instead of the usual fictitious and conceptually inconsistent hopping algorithms. The effects and advantages of the proposed scheme are preliminarily illustrated by a two-surface model system.     

量子分子动力学模拟液体钚的输运性质

采用第一原理分子动力学（QMD）方法模拟液体钚的输运性质.计算的粘性和扩散系数在较低温度时与文献有明显差异,在实验测量范围内,模拟结果与实验一致,温度升高时数值模拟结果趋于一致.利用QMD的模拟结果计算了应力自相关函数和速度自相关函数,结果表明：在温度较低时,液体钚呈现明显的强关联特性.对于具有强关联特性的液体,利用较短时间的QMD模拟结果,通过简单e指数拟合外推到t→∞得到的扩散系数和粘性具有较大偏差,这是造成本文模拟结果与文献结果出现差异的主要原因.通过增加QMD模拟时间步数,获得了更为准确的输运性质.     

Quantum Trajectory Approach to Molecular Dynamics Simulation with Surface Hopping

In this work we propose a quantum trajectory approach to the powerful molecular dynamics simulation with surface hopping,from an insight that an efectiveobservationis actually implied in the simulation through tracking the forces experienced,just like checking the meter’s result in quantum measurement process.This treatment can build the nonadiabatic surface hopping on a physical foundation,instead of the usual fictitious and conceptually inconsistent hopping algorithms.The efects and advantages of the proposed scheme are preliminarily illustrated by a two-surface model system.     

Preservation of Quantum Coherence for Gaussian-State Dynamics in a Non-Markovian Process

Coherence is a key resource in quantum information science.Exactly understanding and controlling the variation of coherence are vital for implementation in realistic quantum systems.Using P-representation of density matrix,we obtain the analytical solution of the master equation for the classical states in the non-Markovian process and investigate the coherent dynamics of Gaussian states.It is found that quantum coherence can be preserved in such a process if the coupling strength between system and environment exceeds a threshold value.We also discuss the characteristic function of the Gaussian states in the non-Markovian process,which provides an inevitable bridge for the control and operation of quantum coherence.     

中能重离子碰撞中多重碎裂的同位旋效应

利用同位旋相关的量子分子动力学,研究了逆反应系统¹²⁰Xe+⁴⁰Ca,¹²⁰Cd+⁴⁰Ar和⁷⁶Kr+⁴⁰Ca,⁷⁶Zn+⁴⁰Ar中多重碎裂的同位旅效应.对于在中能区缺中子碰撞系统的中等质量碎片多重性大于丰中子碰撞系统的现象进行了分析和讨论.     

Portable Implementation of a Quantum Thermal Bath for Molecular Dynamics Simulations

Recently, Dammak and coworkers (Phys. Rev. Lett. 103:190601, 2009) proposed that the quantum statistics of vibrations in condensed systems at low temperature could be simulated by running molecular dynamics simulations in the presence of a colored noise with an appropriate power spectral density. In the present contribution, we show how this method can be implemented in a flexible manner and at a low computational cost by synthesizing the corresponding noise ‘on the fly’. The proposed algorithm is tested for a simple harmonic chain as well as for a more realistic model of aluminium crystal. The energy and Debye-Waller factor are shown to be in good agreement with those obtained from harmonic approximations based on the phonon spectrum of the systems. The limitations of the method associated with anharmonic effects are also briefly discussed. Some perspectives for disordered materials and heat transfer are considered.     

对中能重离子碰撞碎块形成过程中核结构效应的研究

在一般的量子分子动力学模型(QMD)的基础上,通过考虑重构模型(RAM),中子、质子区分,核子费米性质的描述以及利用摩擦冷却方法(FCM)来对核基态抽样,得到一种改进的量子分子动力学模型(MQMD).然后,在改进的量子分子动力学模型的基础上研究了¹²C+¹²C在E_lab=28.7MeV/u时一些同位素的分布及其时间稳定性.结果表明,改进的量子分子动力学模型能够很好地描述重离子碰撞中碎块形成的核结构效应.     

Quantum Potential in Relativistic Dynamics

The experimental confirmation of nonlocality has renewed interest in Bohm's quantum potential. The construction of quantum potentials for relativistic systems has encountered difficulties which do not arise in a parametrized formulation of relativistic quantum mechanics known as Relativistic Dynamics. The purpose of this paper is to show how to construct a quantum potential in the relativistic domain by deriving a relativistically invariant quantum potential using Relativistic Dynamics. The formalism is applied to three relativistic scalar particle models: a single particle interacting with a scalar potential; N particles interacting with a scalar potential; and a single particle interacting with an electromagnetic 4-vector potential.     

重离子碰撞中能量储藏同入射道动力学的关系

用仅密度相关的ＢＵＵ模型讨论了在重离子碰撞中能量储藏与入射道动力学（入射能、碰撞参数、碰撞系统）的依赖关系，以及碰撞系统的极不对称性对激发能的影响．     

Measurement of Rotational Temperature by Simulated Molecular Spectra

The measurement of temperature of heavy particles in a thermal plasma is based on the comparison of experimental rotational spectrum obtained by optical emission Spectroscopy and synthetic spectra calculated for different temperatures. The calculation principle of the synthetic spectra is detailed as well as the temperature accuracy obtained. This method is used to measure the temperature of an Ar-CO₂ mixture plasma produced in a wall stabilized arc with molecular spectra of C₂ (Swan system) and CN (violet system).     

Hilbert Modules in Quantum Electro Dynamics and Quantum Probability

A physical system of the form with a distinguished state on may be described in a natural way on a Hilbert -module. Following the ideas of Accardi and Lu [1], we apply this possibility to a concrete system consisting of a boson field in the vacuum state coupled to a free electron. We show that the physical system is described adequately on a new type of Fock module: the symmetric Fock module. It turns out that a module has to fulfill an algebraic condition in order to allow for the construction of a symmetric Fock module. We prove in a central limit theorem that in the stochastic limit the moments of the collective operators (i.e. more or less the time-integrated interaction Hamiltonian) converge to the moments of free creators and annihilators on a full Fock module. In the sense of Voiculescu [22] and Speicher [20] these operators form a free white noise over the algebra . Received: 28 October 1996 / Accepted: 21 July 1997     

在量子分子动力学模型中与N,Z有关的宏观势对碎片形成的影响

基于QuantumMolecularDynamics(QMD)模型,在Skyrme类型势,Yukawa和库仑相互作用势外,又考虑了与碎片集团的中子、质子数相关的宏观势,即波滴模型中的对称能再加上壳修正能和对修正能.这样的考虑改善了中能重离子反应中集团形成的合理结构.     

Carrier Dynamics in Quantum Well Lasers

A fully microscopic theory is used to perform an analysis of carrier–carrier and carrier-LO phonon scattering in semiconductor quantum wells, focussing on the high-density case relevant for laser structures. A large variance of scattering times is observed depending on the material parameters, apparently contradicting popular belief in some cases. For instance, carrier–carrier scattering may slow down when the carrier density is increased. Electron-hole scattering times are found to be on the same order of magnitude as carrier-phonon scattering, making the introduction of a separate electron and hole temperature necessary. Heating by optical pumping is investigated and plasma cooling is shown to be possible by optical pumping of the laser structure.