Canarie Elizabeth R, Jahn Samuel M, Stoll Stefan
Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
J Phys Chem Lett. 2020 May 7;11(9):3396-3400. doi: 10.1021/acs.jpclett.0c00768. Epub 2020 Apr 17.
The decoherence, or dephasing, of electron spins in paramagnetic molecules limits sensitivity and resolution in electron paramagnetic resonance spectroscopy, and it represents a challenge for utilizing paramagnetic molecules as qubit units in quantum information devices. For organic radicals in dilute frozen aqueous solution at cryogenic temperatures, electron spin decoherence is driven by neighboring nuclear spins. Here, we show that this nuclear-spin-driven decoherence can be quantitatively predicted from the molecular structure and solvation geometry of the radicals. We use a fully deterministic quantum model of the electron spin and up to 2000 neighboring protons with a static spin Hamiltonian that includes nucleus-nucleus couplings. We present experiments and simulations of two nitroxide radicals and one trityl radical, which have decoherence time scales of 4-5 μs below 60 K. We show that nuclei within 12 Å of the electron spin contribute to decoherence, with the strongest impact from protons 4-8 Å away.
顺磁性分子中电子自旋的退相干或去相位限制了电子顺磁共振光谱的灵敏度和分辨率，这对于在量子信息设备中使用顺磁性分子作为量子比特单元而言是一项挑战。对于低温下稀冷冻水溶液中的有机自由基，电子自旋退相干由相邻的核自旋驱动。在此，我们表明这种核自旋驱动的退相干可以从自由基的分子结构和溶剂化几何结构进行定量预测。我们使用电子自旋的完全确定性量子模型以及多达2000个具有静态自旋哈密顿量的相邻质子，该哈密顿量包括核 - 核耦合。我们展示了两种氮氧化物自由基和一种三苯甲基自由基的实验与模拟结果，它们在60 K以下的退相干时间尺度为4 - 5微秒。我们表明，距离电子自旋12 Å以内的核会对退相干产生影响，其中距离4 - 8 Å的质子影响最强。
