从半导体双量子点Heisenberg自旋三元组导出真正的去相干自由子空间
True decoherence-free-subspace derived from a semiconductor double quantum dot Heisenberg spin-trimer
AI总结：
从半导体双量子点Heisenberg自旋三元组导出真正的去相干自由子空间，用于保护量子比特免受磁场波动影响。
摘要：
固态系统中的自旋可以本质上作为量子模拟或量子信息处理的量子比特。自旋量子比特通常容易受到环境磁场波动的影响；然而，将自旋量子比特编码在去相干自由子空间（DFS）中可以对其保护，具体取决于DFS的结构。在这里，我们从一个反铁磁性Heisenberg自旋-1/2三元组导出“真正的”DFS，该DFS能够保护量子比特状态免受短波和长波磁场波动的影响。我们定义了由三个电子限制在门定义的GaAs双量子点（DQD）中的自旋三元组，其中我们利用其中一个量子点中的Wigner-分子化。我们首先利用三元组进行动态核极化（DNP），这会生成显著的磁场差异ΔB_z，这在DQD内产生。我们显示，大的ΔB_z显著改变了三元组的本征谱，并导致DQD中的“真正的”DFS。实时贝叶斯估计DFS能量间隙明确展示了DFS对短波和长波磁场波动的保护作用。我们的发现为交换耦合量子点自旋链的紧凑DFS结构铺平了道路，其内部结构可以完全相干地控制，完全脱离环境磁场的影响。
英文摘要：
Spins in solid systems can inherently serve as qubits for quantum simulation or quantum information processing. Spin qubits are usually prone to environmental magnetic field fluctuations; however, a spin qubit encoded in a decoherence-free-subspace (DFS) can be protected from certain degrees of environmental noise depending on the specific structure of the DFS. Here, we derive the "true" DFS from an antiferromagnetic Heisenberg spin-1/2 trimer, which protects the qubit states against both short- and long-wavelength magnetic field fluctuations. We define the spin trimer with three electrons confined in a gate-defined GaAs double quantum dot (DQD) where we exploit Wigner-molecularization in one of the quantum dots. We first utilize the trimer for dynamic nuclear polarization (DNP), which generates a sizable magnetic field difference, $ΔB_\mathrm{z}$, within the DQD. We show that large $ΔB_\mathrm{z}$ significantly alters the eigenspectrum of the trimer and results in the "true" DFS in the DQD. Real-time Bayesian estimation of the DFS energy gap explicitly demonstrates protection of the DFS against short-wavelength magnetic field fluctuations in addition to long-wavelength ones. Our findings pave the way toward compact DFS structures for exchange-coupled quantum dot spin chains, the internal structure of which can be coherently controlled completely decoupled from environmental magnetic fields.
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