发表机构
Massachusetts Institute of Technology; The University of New South Wales; Diraq（麻省理工学院; 新南威尔士大学; Diraq）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究利用Si/SiGe的固有核自旋磁场梯度，开发了无外加磁场的量子点交换振荡表征工具，延长了量子比特相干时间，实现了剩余交换的高分辨率表征。
AI 中文摘要
基于交换的半导体量子比特包含一大类由类单重态和类三重态自旋态构成的编码，其中若干种编码可在零外加磁场下工作。它们的可靠运行需要对环境噪声、剩余空闲相互作用以及依赖交换的衰减进行表征，但这类表征通常依赖多轴控制校准或刻意设计的磁场梯度。更简单的零外加磁场诊断方法对混合半导体-超导体系统尤为重要，因为磁场会劣化超导组件。本研究中，我们利用同位素富集Si/SiGe中剩余核自旋产生的固有磁场梯度，将两个量子点之间的交换振荡作为表征工具，无需微磁体、动态核极化或预先的多轴校准。使用Carr-Purcell-Meiboom-Gill交换序列，我们将单重态相干时间从T₂*=1.17±0.02 μs延长至T₂^CPMG=74.8±1.8 μs（N=70个重聚焦脉冲）。振荡相位可分辨数十千赫兹范围内的剩余交换，并能将其映射到(1,1)电荷单元上。这些结果确立了固有梯度交换振荡作为一种简单、更具相关性的零场诊断方法，适用于仅交换及相关半导体量子比特编码，可实现快速、高通量的器件表征。
英文摘要
Exchange-based semiconductor qubits encompass a broad family of encodings constructed from singlet- and triplet-like spin states, several of which are compatible with operation at zero applied magnetic field. Their reliable operation requires characterization of environmental noise, residual idle interactions, and exchange-dependent decay, but this characterization often relies on multi-axis control calibration or deliberately engineered magnetic-field gradients. A simpler zero-applied-field diagnostic is particularly valuable for hybrid semiconductor-superconductor systems, in which magnetic fields can degrade superconducting components. Here, we use the intrinsic magnetic-field gradient produced by residual nuclear spins in isotopically enriched Si/SiGe to implement exchange oscillations between two quantum dots as a characterization tool without a micromagnet, dynamic nuclear polarization, or prior multi-axis calibration. Using Carr-Purcell-Meiboom-Gill exchange sequences, we extend the singlet coherence from $T_2^*=1.17\pm0.02~μ$s to $T_2^{\mathrm{CPMG}}=74.8\pm1.8~μ$s with $N=70$ refocusing pulses. The oscillation phase resolves residual exchange in the tens-of-kilohertz regime and enables it to be mapped across the $(1,1)$ charge cell. These results establish intrinsic-gradient exchange oscillations as a simple, more relevant zero-field diagnostic for exchange-only and related semiconductor qubit encodings that is amenable to rapid, high-throughput device characterization.
