共查询到20条相似文献,搜索用时 875 毫秒
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利用量子不变量理论研究了任意随变化的强磁场中碱金属原子系统的演化问题,得到了此精确的演化态,并利用此精确的演化态求出了相应的Aharonov-Anandan相因子和绝热极限下的Berry相因子。将此系统精确的演化按哈密顿量的瞬音本征态展开,可以得到绝热近似似的任意阶修正。 相似文献
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最近提出的一个构建相干态的方案中,需要精确求解一个时间相关的常微分方程.基于代数动力学理论,利用该方程具有的SU(1,1)动力学对称性,提出了对此方程在含时系数取任意函数形式时的统一的精确求解方法,并且得到了严格的解析解.运用这个精确解,就可以构造相应物理系统的精确相干态的具体表达式.给出了一个解例,即频率取"快变"函数的情形.利用得到的精确结果,讨论了这个系统的量子涨落(量子噪声)随时间演化的情况.针对动量算符不确定度随时间演化的曲线的性态,指出在制备这个系统压缩态时可以利用的一些性质.最后,讨论了这个量子系统的不确定关系随时间演化的情况. 相似文献
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本文利用高阶量子绝热近似方法讨论了量子微腔驻波场中三能级暗态原子与光场相互作用中原子质心运动对电子,光场系统动力学的影响。文章分析了绝热近似成立的条件以及非绝热因子对动力学演化的影响。文中还计算了原子在腔中的非绝热跃迁几率及各部分能量分布的平均值。 相似文献
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In this paper, the exact evolving state for a two-level quantum system is found by making use of the Lewis-Riesenfeld invariant theory. In principle, the correction to an arbitrary order in the adiabatic approximation parameter c can be obtained from this exact evolving state. To the n-th order in ∈, it is shown that the exact evolving state reduces to the superadiabatic basis introduced by Berry recently. The Aharonov-Anandan phase and its adiabatic limit (Berry phase for the system) are also calculated. e for the system) are also calculated. 相似文献
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A reasonable physical intuition in the study of interacting quantum systems says that, independent of the initial state, the system will tend to equilibrate. In this work we introduce an experimentally accessible setting where relaxation to a steady state is exact, namely, for the Bose-Hubbard model quenched from a Mott quantum phase to the free strong superfluid regime. We rigorously prove that the evolving state locally relaxes to a steady state with maximum entropy constrained by second moments--thus maximizing the entanglement. Remarkably, for this to be true, no time average is necessary. Our argument includes a central limit theorem and exploits the finite speed of information transfer. We also show that for all periodic initial configurations (charge density waves) the system relaxes locally, and identify experimentally accessible signatures in optical lattices as well as implications for the foundations of statistical mechanics. 相似文献
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The time evolution of the time-dependent harmonic oscillator is studied by a sequence of unitary transformations and the exact evolving state for the system is obtained. A specific model of frequency variation for the time-dependent harmonic oscillator is discussed as an illustrative example. 相似文献
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The Lewis'invariant and exact solution for the driven generalized time-dependent harmonic oscillator is found by making use of the Lewis-Riesenfeld quantum theory. Then, the adiabatic asymptotic limit of the exact solution is discussed and the Berry's phase for thirr system is obtained. We then proceed to use the exact solution to construct the coherent state and calculate the corresponding exact classical phase angle. This phase angle can give the Hannay's angle in the adiabatic limit. The relation between the exact Lewis'phase and the corresponding classical phase angle L'discusrred. 相似文献
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We use the exact Nakajima–Zwanzig form of the master equation to show that open quantum systems which exhibit equilibration (or thermalization) by evolving to a time independent asymptotic state, have under certain conditions a reduced density matrix for the system which commutes with the effective system Hamiltonian. We also show that if the initial system–bath density matrix is of product form then the asymptotic reduced density matrix of the system depends only on the diagonal elements of the initial system density matrix in the eigenbasis of the effective Hamiltonian. 相似文献
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D. Hennig C. Mulhern 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):1
We consider the dynamics for a system consisting of three coupled, driven and damped
particles evolving in a symmetric and spatially-periodic potential landscape. The three
coupled particles, known as a trimer, form a one-dimensional chain. Our main focus is
concentrated on running solutions for this system. In particular, we explore the nature of
these solutions. Therefore, proofs are derived showing that for the three coupled
particles in a running state 1) each particle travels the same distance in a single period
and, 2) there is only one possible transport scenario – namely when the particles travel
in rod-like motion. It is also shown that in such a state, the particles, evolving on a
periodic attractor, no longer exchange energy with one another. Thus in a running state
the three-particle system, evolving in general in a high-dimensional phase space,
effectively reduces to a single-particle system and motion takes place on a lower
dimensional attractor, viz. a limit cycle. Furthermore analysis is carried out exploring
how the frequency of the driving affects coherent particle transport. Numerical evidence
demonstrates that there is a small window of frequencies for which (low-dimensional) limit
cycles exist allowing for directed particle transport to occur. 相似文献
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Electromagnetically induced transparency is an effect observed in atomic systems, originating from quantum interference, in which electromagnetic transitions to and from a certain quantum state become suppressed. This dark state is also characterized by a quantum phase, relative to other states, which theoretically should stop evolving, but remain phase coherent, during transparency. We test this theoretical prediction using techniques developed for liquid-state nuclear magnetic resonance quantum computation, applied to a spin-7/2 nuclear spin system. A sequence of quantum operations is applied to create the dark state, and during transparency its phase evolution is measured relative to a reference state using Ramsey interferometry. Experimental measurements of the fringe visibility are in excellent agreement with theoretical expectations, taking into account measured decoherence rates. 相似文献
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Huang Yun Rao Hua Lan Xu Guo Lan Fu Yi Bao Liu Bo Lv Yan Yan Jiang Yan Xia Yu 《International Journal of Theoretical Physics》2014,53(6):1797-1803
Geometric phase of mixed state is investigated for three-level system obeying a high-temperature master equation. The results show the Berry phase of mixed phase is strongly dependent on the initial condition. For the different initial angle, the turning region is different. In addition, the decrease of Berry phase is most slow around the coupling strength α=5 with an increasing of evolving time. 相似文献
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We investigate a reformulation of the dynamics of interacting fermion systems in terms of a stochastic extension of time-dependent Hartree-Fock equations. From a path-integral representation of the evolution operator, we show that the exact N-body state can be interpreted as a coherent average over Slater determinants evolving in a random mean-field. The imaginary time propagation is also presented and gives a similar scheme which converges to the exact ground state. In addition, the growth of statistical errors is examined to show the stability of this stochastic formulation. 相似文献
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We study the ground state and low-energy excitation of dimer XXZ spin ladder with Heisenberg and XXZ interactions along the rung and rail directions, respectively. Using a bond operator method, we get low-energy effective Hamiltonians in different parameter regions. Based on those low-energy effective Hamiltonians, we set up the ground state phase diagrams and investigate the properties of low-energy excitation in each phase. We will show that the results are exact one when the XXZ interactions along rail reduce to the Ising type. The quantum Monte Carlo and exact diagonalization methods are also applied to the finite system to verify the exact nature of the phases, the phase transitions and the low-energy excitation. Of all the phases, we pay a special attention to the gapped antiferromagnetic phase, which is disclosed to be a non-trivial one that exhibits the time-reversal symmetry. We also discuss how our findings could be realized and detected by using cold atoms in optical lattice. 相似文献