利用锗自旋量子比特中的各向异性交换实现两量子比特门
Engineering two-qubit gates via anisotropic exchange in germanium spin qubits
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中文总结 AI 辅助
本研究利用应变锗量子阱中的两个空穴自旋量子比特，结合磁场全矢量控制测绘交换张量，通过磁场取向调谐实现纵向与横向交换分量的调控，成功实现各向同性交换无法得到的单脉冲基带 iSWAP 门，建立了原生哈密顿量工程。
中文摘要 AI 辅助
锗空穴自旋量子比特是量子计算与量子模拟的一种极具前景且用途广泛的平台。在该体系中，强自旋轨道相互作用（SOI）使单量子比特的g张量呈现各向异性，且可通过电学方式调谐，从而能得到噪声敏感性降低的工作 sweet spot（ sweet spot 指性能优异的工作点）。SOI 还将各向同性的两量子比特交换耦合转化为各向异性张量，其几何结构源自单量子比特的g张量与自旋翻转隧穿。本研究中，我们利用应变锗量子阱中的两个空穴自旋量子比特，并结合磁场的全矢量控制，对该交换张量进行测绘，将其分离为纵向与横向分量，结果表明二者分别受控于受控相位（controlled-phase）类动力学与类 SWAP 动力学。我们发现，纵向交换可通过磁场取向调谐，从常规正值经零值变为有效负值，这一结果通过反转的交换分裂自旋跃迁得到证实。因此，磁场方向可对相互作用哈密顿量实现连续控制：在纯横向交换的节点处，我们实现了单脉冲基带 iSWAP 门，这是各向同性交换条件下无法实现的。将 g 张量几何结构与交换各向异性关联，建立了原生哈密顿量工程，仅通过全局磁场取向即可实现基于自旋的量子模拟与门组选择。
英文摘要
Germanium hole spin qubits are a promising and versatile platform for quantum computation and simulation. In this system, strong spin-orbit interaction (SOI) renders the single-qubit $g$-tensor anisotropic and electrically tunable, enabling operational sweet spots with reduced noise sensitivity. SOI also transforms the isotropic two-qubit exchange coupling into an anisotropic tensor whose geometry is inherited from the single-qubit $g$-tensors and spin-flip tunnelling. Here, using two hole spin qubits in a strained-germanium quantum well and full vector control of the magnetic field, we map this exchange tensor, separate it into longitudinal and transverse components, and show that they govern controlled-phase and SWAP-like dynamics, respectively. We find that the longitudinal exchange can be tuned via the magnetic field orientation from a conventional positive value, through zero, to an effectively negative one, as measured by inverted exchange-split spin transitions. The magnetic field direction thus provides continuous control over the interaction Hamiltonian: at a point of purely transverse exchange, we engineer a single-pulse baseband iSWAP, unattainable under isotropic exchange. Linking $g$-tensor geometry to exchange anisotropy establishes native Hamiltonian engineering, enabling spin-based quantum simulation and gate sets selected by the global field orientation alone.
