Decoherence by a spin thermal bath: Role of spin-spin interactions and initial state of the bath
Decoherence by a spin thermal bath: Role of spin-spin interactions and initial state of the bath
复制标题
自旋热浴的退相干：自旋-自旋相互作用的作用和浴的初始状态
DOI：
10.1103/physrevb.77.184301
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发表时间：
2008
影响因子：
3.7
通讯作者：
H. Raedt
中科院分区：
文献类型：
--
作者：
S. Yuan;M. Katsnelson;H. Raedt
我们研究了与自旋浴环境相互作用的两个耦合自旋的退相干。结果表明，环境中自旋之间的连接性和耦合强度对中心系统的消相干是至关重要的。对于各向异性自旋浴，改变连接性或耦合强度可以使中心系统的退相干从高斯衰减律变为指数衰减律。环境的初始状态以一种定性的显著方式影响消相干过程。了解量子自旋系统中的退相干是许多评论著作的主题，请参阅参考文献。1和2.这个问题似乎非常复杂，尽管做了很多努力，但即使是关于退相干过程性质的一些基本问题也仍然没有解决。由于与熔池自旋之间的相互作用，在特殊情况下可以进行分析处理，即使中央系统只包含一个自旋。最近的研究表明，环境的内部动力学可能对中央系统的消相干至关重要。3-15在本文中，我们给出了双自旋系统与自旋浴环境相互作用的大量模拟工作的结果，结果表明，双自旋系统的退相干可以表现出不同的行为，这取决于与环境的耦合特性、内部动力学和后者的初态。我们还提供了一张简单的物理图片来理解这种行为。一般而言，开放量子系统的行为关键取决于中心系统Ec和能量Ece的典型能量差之比，这表征了中心系统与环境的相互作用。与“薛定谔猫”问题有关的ECEce情况已经被广泛地研究过，并且物理上是相当清楚的：16，17作为时间演化的结果，中心系统转移到“指针态”17之一，在这种情况下，它是相互作用哈密顿HCE的本征态。有一个猜想是，在这种情况下，指针态应该是中心系统的哈密顿本征态，但这一点只在一个非常简单的模型中得到了证明。另一方面，如果中心系统由电子自旋组成，而环境是核自旋，例如，如果考虑到使用分子磁铁进行量子计算的可能性，这种情况是主要感兴趣的。19，20
We study the decoherence of two coupled spins that interact with a spin-bath environment. It is shown that the connectivity and the coupling strength between the spins in the environment are of crucial importance for the decoherence of the central system. For the anisotropic spin bath, changing the connectivity or coupling strength changes the decoherence of the central system from Gaussian to exponential decay law. The initial state of the environment is shown to affect the decoherence process in a qualitatively significant manner. I. INTRODUCTION Understanding the decoherence in quantum spin systems is a subject of numerous works for reviews, see Refs. 1 and 2. The issue seems to be very complicated and despite many efforts, even some basic questions about the character of the decoherence process are yet unsolved. Due to the interactions with and between the spin of the bath, an analytical treatment can be carried out in exceptional cases, even if the central systems contain one spin only. Recent work suggests that the internal dynamics of the environment can be crucial to the decoherence of the central system. 3‐15 In this paper, we present results of extensive simulation work of a two-spin system interacting with a spin-bath environment and show that the decoherence of the two-spin system can exhibit different behaviors, depending on the characteristics of the coupling with the environment, the internal dynamics, and the initial state of the latter. We also provide a simple physical picture to understand this behavior. In general, the behavior of an open quantum system crucially depends on the ratio of typical energy differences of the central system Ec and the energy Ece, which characterizes the interaction of the central system with the environment. The EcEce case has been extensively studied in relation to the “Schrodinger cat” problem and the physics is quite clear: 16,17 As a result of time evolution, the central system passes to one of the “pointer states” 17 that, in this case, are the eigenstates of the interaction Hamiltonian Hce .I n the opposite case, E c E ce is less well understood. There is a conjecture that, in this case, the pointer states should be the eigenstates of the Hamiltonian H c of the central system, but this has been proven for a very simple model only. 18 On the other hand, this case is of primary interest if, say, the central system consists of electron spins whereas the environment is nuclear spins, for instance, if one considers the possibility of quantum computation by using molecular magnets. 19,20