Astner T, Gugler J, Angerer A, Wald S, Putz S, Mauser N J, Trupke M, Sumiya H, Onoda S, Isoya J, Schmiedmayer J, Mohn P, Majer J
Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Vienna, Austria.
Institute of Applied Physics, TU Wien, Vienna, Austria.
Nat Mater. 2018 Apr;17(4):313-317. doi: 10.1038/s41563-017-0008-y. Epub 2018 Feb 12.
Longitudinal relaxation is the process by which an excited spin ensemble decays into its thermal equilibrium with the environment. In solid-state spin systems, relaxation into the phonon bath usually dominates over the coupling to the electromagnetic vacuum. In the quantum limit, the spin lifetime is determined by phononic vacuum fluctuations . However, this limit was not observed in previous studies due to thermal phonon contributions or phonon-bottleneck processes. Here we use a dispersive detection scheme based on cavity quantum electrodynamics to observe this quantum limit of spin relaxation of the negatively charged nitrogen vacancy (NV) centre in diamond. Diamond possesses high thermal conductivity even at low temperatures , which eliminates phonon-bottleneck processes. We observe exceptionally long longitudinal relaxation times T of up to 8 h. To understand the fundamental mechanism of spin-phonon coupling in this system we develop a theoretical model and calculate the relaxation time ab initio. The calculations confirm that the low phononic density of states at the NV transition frequency enables the spin polarization to survive over macroscopic timescales.
纵向弛豫是指一个受激自旋系综衰变为与环境处于热平衡状态的过程。在固态自旋系统中，向声子库的弛豫通常比与电磁真空的耦合占主导地位。在量子极限下，自旋寿命由声子真空涨落决定。然而，由于热声子贡献或声子瓶颈过程，在先前的研究中并未观察到这一极限。在这里，我们使用基于腔量子电动力学的色散检测方案来观察金刚石中带负电的氮空位（NV）中心自旋弛豫的这一量子极限。即使在低温下，金刚石也具有高导热性，这消除了声子瓶颈过程。我们观察到长达8小时的超长纵向弛豫时间T。为了理解该系统中自旋 - 声子耦合的基本机制，我们开发了一个理论模型并从头计算弛豫时间。计算结果证实，NV跃迁频率处的低声子态密度使得自旋极化能够在宏观时间尺度上得以保留。
