Gelman David, Koch Christiane P, Kosloff Ronnie
Fritz Haber Research Center for Molecular Dynamics, Hebrew University of Jerusalem, Jerusalem, 91904, Israel.
J Chem Phys. 2004 Jul 8;121(2):661-71. doi: 10.1063/1.1759312.
The dissipative quantum dynamics of an anharmonic oscillator coupled to a bath is studied with the purpose of elucidating the differences between the relaxation to a spin bath and to a harmonic bath. Converged results are obtained for the spin bath by the surrogate Hamiltonian approach. This method is based on constructing a system-bath Hamiltonian, with a finite but large number of spin bath modes, that mimics exactly a bath with an infinite number of modes for a finite time interval. Convergence with respect to the number of simultaneous excitations of bath modes can be checked. The results are compared to calculations that include a finite number of harmonic modes carried out by using the multiconfiguration time-dependent Hartree method of Nest and Meyer [J. Chem. Phys. 119, 24 (2003)]. In the weak coupling regime, at zero temperature and for small excitations of the primary system, both methods converge to the Markovian limit. When initially the primary system is significantly excited, the spin bath can saturate restricting the energy acceptance. An interaction term between bath modes that spreads the excitation eliminates the saturation. The loss of phase between two cat states has been analyzed and the results for the spin and harmonic baths are almost identical. For stronger couplings, the dynamics induced by the two types of baths deviate. The accumulation and degree of entanglement between the bath modes have been characterized. Only in the spin bath the dynamics generate entanglement between the bath modes.
研究了与浴耦合的非谐振子的耗散量子动力学，目的是阐明弛豫到自旋浴和谐振子浴之间的差异。通过替代哈密顿量方法获得了自旋浴的收敛结果。该方法基于构建一个系统 - 浴哈密顿量，其中包含有限但大量的自旋浴模式，在有限的时间间隔内精确模拟具有无限数量模式的浴。可以检查关于浴模式同时激发数量的收敛性。将结果与使用Nest和Meyer的多配置时间相关哈特里方法[《化学物理杂志》119, 24 (2003)]进行的包含有限数量谐振模式的计算进行比较。在弱耦合区域，在零温度且初级系统小激发的情况下，两种方法都收敛到马尔可夫极限。当初始时初级系统被显著激发时，自旋浴会饱和从而限制能量接受。浴模式之间的一个传播激发的相互作用项消除了饱和。分析了两个猫态之间的相位损失，自旋浴和谐振子浴的结果几乎相同。对于更强的耦合，两种类型的浴诱导的动力学出现偏差。对浴模式之间的纠缠积累和程度进行了表征。只有在自旋浴中，动力学才会在浴模式之间产生纠缠。
