基于量子点的马约拉纳链中量子比特相干性的标度：由四个和六个量子点形成的马约拉纳量子比特的拉比和拉姆齐振荡
Scaling of qubit coherence in quantum dot based Majorana chains: Rabi and Ramsey oscillations of Majorana qubits formed by four and six quantum dots
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中文总结 AI 辅助
本文研究四点与六点量子点马约拉纳链量子比特的拉比和拉姆齐相干时间，发现更长的链是更好的量子存储器，但未必是更好的可操控量子比特。
中文摘要 AI 辅助
我们针对由双N位量子点人工Kitaev链形成的马约拉纳基量子比特，开展了拉比和拉姆齐相干时间的理论研究，该研究紧随最近的实验实现（arXiv:2607.09511）。我们将量子比特推广到任意长度的两条链，并比较了四点量子比特和六点量子比特的拉比和拉姆齐振荡，模拟中采用了真实的 disorder（无序），对应三组参数：小超导能隙、大超导能隙以及实验参数。我们发现，在 pristine（无缺陷）极限下，拉比振荡与链长无关，而六点量子比特的拉姆齐振荡则遭受更大的泄漏，因为第三个位点抑制了远离 sweet spot（最佳工作点）的不希望的能量劈裂，但同时也使得刻意引入的劈裂难以实现，这需要更大的失谐，而失谐可能激发体态。在存在 disorder（无序）的现实情况下，两种相干时间均不会随链长普遍改善。拉比相干时间由三个退相干通道的竞争决定，只有当链间隧穿的涨落被抑制时，额外的量子点才有收益；拉姆齐相干时间由σz旋转期间能量劈裂的涨落决定，对于四点量子比特，该涨落仅由 sweet spot（最佳工作点）处的 disorder（无序）决定，与平均劈裂无关，而对于六点量子比特，产生劈裂的失谐会引入随劈裂本身增长的涨落，因此额外的量子点仅在小劈裂情况下才有收益。这意味着更长的链是更好的量子存储器，但在操控下未必是更好的量子比特。尽管在更长的Kitaev链量子比特中预期存在拓扑保护，但在当前的拉比和拉姆齐测量协议中观测到它仍然是一个实验挑战。
英文摘要
We present a theoretical study of the Rabi and Ramsey coherence time of Majorana-based qubits formed by double $N$-site quantum-dot artificial Kitaev chains, following the recent experimental realization arXiv:2607.09511. We generalize the qubit to two chains of arbitrary length and compare the Rabi and Ramsey oscillations of the four-dot and six-dot qubits, simulated with realistic disorder for three sets of parameters: small and large superconducting gaps, and the experimental parameters. We find that, in the pristine limit, the Rabi oscillation is independent of the chain length, whereas the Ramsey oscillation of the six-dot qubit suffers from larger leakage, because the third site suppresses the unwanted energy splitting away from the sweet spot but at the same time makes the deliberate splitting difficult to achieve, which requires a larger detuning that could excite the bulk. In reality with disorder, neither coherence time improves universally with the chain length. The Rabi coherence is set by the competition of three dephasing channels, and the additional dots pay off only if the fluctuation of the interchain tunneling is suppressed; the Ramsey coherence is set by the fluctuation of the energy splitting during the $σ_z$ rotation, which for the four-dot qubit is fixed by the sweet-spot disorder alone and does not depend on the mean splitting, whereas for the six-dot qubit the detuning that generates the splitting adds a fluctuation growing with the splitting itself, so the additional dots pay off only for small splittings. This implies that a longer chain is thus a better quantum memory but not necessarily a better qubit under manipulation. Although topological protection is expected in a longer Kitaev chain qubit, observing it in the current Rabi and Ramsey measurement protocols remains an experimental challenge.
发表机构
- University of Florida（佛罗里达大学）
- University of Maryland（马里兰大学）
机构由 AI 辅助整理，请以论文原文为准。
