随机性对海森堡自旋链量子数据总线的影响
Effect of Randomness on Quantum Data Buses of Heisenberg Spin Chains
摘要：
强耦合自旋链可以调解远程量子比特之间的长距离有效耦合或纠缠，并且可以用作量子数据总线。我们研究了静态随机交换耦合和磁场对自旋为1/2的海森堡链作为自旋总线的保真度的影响。我们发现，虽然非均匀交换耦合保持量子比特有效耦合的各向同性，但它们导致耦合的能级、本征态和幅度局部变化。另一方面，随机的局部磁场导致总线基态流形避免了能级交叉，并导致有效的量子比特耦合是各向异性的。有趣的是，奇数大小的总线的基态的总磁矩可能不平行于平均磁场。它的排列取决于平均场的方向和场分布，与总是与所施加的磁场对齐以使塞曼能量最小化的单个自旋的基态相反。最后，我们计算的自旋总线的敏感性，这样的局部变化，这是潜在的有用的评估退相干时，在交换耦合或磁场的动态波动被认为是。
英文摘要：
A strongly coupled spin chain can mediate long-distance effective couplings or entanglement between remote qubits, and can be used as a quantum data bus. We study how the fidelity of a spin-1/2 Heisenberg chain as a spin bus is affected by static random exchange couplings and magnetic fields. We find that, while non-uniform exchange couplings preserve the isotropy of the qubit effective couplings, they cause the energy levels, the eigenstates, and the magnitude of the couplings to vary locally. On the other hand, random local magnetic fields lead to an avoided level crossing for the bus ground state manifold, and cause the effective qubit couplings to be anisotropic. Interestingly, the total magnetic moment of the ground state of an odd-size bus may not be parallel to the average magnetic field. Its alignment depends on both the direction of the average field and the field distribution, in contrast with the ground state of a single spin which always aligns with the applied magnetic field to minimize the Zeeman energy. Lastly, we calculate sensitivities of the spin bus to such local variations, which are potentially useful for evaluating decoherence when dynamical fluctuations in the exchange coupling or magnetic field are considered.
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