Huang Peihao, Zimmerman Neil M, Bryant Garnett W
Joint Quantum Institute, National Institute of Standards and Technology and University of Maryland, Gaithersburg, MD 20899, USA.
Quantum Measurement Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
npj Quantum Inf. 2018;4(1). doi: 10.1038/s41534-018-0112-0.
Rapid progress in semiconductor spin qubits has enabled experimental demonstrations of a two-qubit logic gate. Understanding spin decoherence in a two-qubit logic gate is necessary for optimal qubit operation. We study spin decoherence due to charge noise for two electrons in a double quantum dot used for a two-qubit controlled-phase gate. In contrast to the usual belief, spin decoherence can be dominated by the tunneling noise from charge noise instead of the detuning noise. Tunneling noise can dominate because the effect of tunneling noise on the spin qubit is first order in the charge admixture; while the effect of the detuning noise is only second order. The different orders of contributions result in different detuning dependence of the decoherence, which provides a way to identify the noise source. We find that decoherence in a recent two-qubit experiment was dominated by the tunneling noise from charge noise. The results illustrate the importance of considering tunneling noise to design optimal operation of spin qubits.
半导体自旋量子比特的快速发展使得两比特逻辑门的实验演示成为可能。了解两比特逻辑门中的自旋退相干对于优化量子比特操作至关重要。我们研究了用于两比特控制相位门的双量子点中两个电子因电荷噪声引起的自旋退相干。与通常的看法相反，自旋退相干可能主要由电荷噪声产生的隧穿噪声而非失谐噪声主导。隧穿噪声能够占据主导地位，是因为隧穿噪声对自旋量子比特的影响在电荷混合中是一阶的；而失谐噪声的影响仅是二阶的。不同阶次的贡献导致退相干对失谐的依赖性不同，这为识别噪声源提供了一种方法。我们发现，近期一个两比特实验中的退相干主要由电荷噪声产生的隧穿噪声主导。这些结果说明了在设计自旋量子比特的最佳操作时考虑隧穿噪声的重要性。
