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arXiv 1611.07186quant-phcond-mat.mes-hall
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双量子点系统的能谱、交换作用和门串扰:分子轨道计算

Energy spectrum, exchange interaction and gate crosstalk in a pair of double-quantum-dot system: a molecular orbital calculation

Xu-Chen Yang, Xin Wang

摘要:

我们基于分子轨道方法对一个四电子四量子点系统进行了理论研究,该系统包含一对单重态-三重态自旋量子比特。我们明确地考虑到在所有的点的电子波函数的混合,并已发现,这种混合的波函数的能谱,交换相互作用和系统的门串扰的后果。具体地说,我们发现当两个单重态-三重态量子比特足够接近时,一些态不再由计算基态主导,交换相互作用不能简单地理解为单重态和三重态之间的能量差。使用Hund-Mulliken计算的Hubbard参数,我们表征的有效交换相互作用的系统,并已发现良好的协议与计算结果通过采取能量差在适用的情况下。我们研究了两种通常设想的耦合两个量子比特的方案,交换耦合和电容耦合,并且发现当量子比特间的距离处于某些中间值时,这两种耦合的强度相当,使两个量子比特的演化分析复杂化。我们还研究了由于电子态的量子力学混合而导致的系统中的门串扰,并且发现虽然这种效应通常非常弱,但如果量子位之间的间距类似于或小于构成量子位的双点之间的距离,则不应忽略这种效应。

英文摘要:

We present a theoretical study of a four-electron four-quantum-dot system based on molecular orbital methods, which hosts a pair of singlet-triplet spin qubits. We explicitly take into account of the admixture of electron wave functions in all dots, and have found that this mixing of wave functions has consequences on the energy spectrum, exchange interaction and the gate crosstalk of the system. Specifically, we have found that when the two singlet-triplet qubits are close enough, some of the states are no longer dominated by the computational basis states and the exchange interaction can not simply be understood as the energy difference between the singlet and triplet states. Using the Hund-Mulliken calculation of the Hubbard parameters, we characterize the effective exchange interaction of the system and have found good agreement with results calculated by taking energy differences where applicable. We have studied the two commonly conceived schemes coupling two qubits, the exchange and capacitive coupling, and have found that when the inter-qubit distance is at certain intermediate values, the two kinds of coupling are comparable in strength, complicating analyses of the evolution of the two qubits. We also investigate the gate crosstalk in the system due to the quantum mechanical mixing of electron states and have found that while this effect is typically very weak, it should not be ignored if the spacing between the qubits are similar to or less than the distance between the double dots that constitute the qubit.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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