发表机构
Indian Institute of Technology Roorkee; Indian Institute of Engineering Science and Technology, Shibpur; Indian Institute of Technology (ISM) Dhanbad（印度理工学院卢达克内; 印度工程科学学院希布尔分校; 印度理工学院（ISMT）丹巴德）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究建立荧光蛋白自旋量子比特弛豫测量的探测极限理论，发现室温下其生理灵敏度不足，提出发色团环境刚度提升等设计规则以优化传感性能。
AI 中文摘要
增强型黄色荧光蛋白在其亚稳态三重态中包含一个光学可寻址的自旋-1量子比特，这一发现为分子尺度的基因编码量子传感提供了可能性。我们开发了一种探测极限理论，用于利用该荧光蛋白自旋量子比特（FPSQ）通过自旋弛豫测量来感知顺磁性神经信号自由基。我们推导了零场分裂三重态与扩散自由基浴耦合的跃迁分辨Redfield弛豫矩阵，确定了其坍缩为单指数的区域，并通过Lindblad模拟和氮空位（NV）基准对其进行了验证。结合光子散粒噪声、基于光漂白的光子预算以及有限测量带宽的影响，我们发现天然室温传感器的生理灵敏度不足6至8个数量级，瓶颈在于声子限制的本征自旋-晶格弛豫时间（T₁）。分析潜在的直接和双声子拉曼过程表明，室温弛豫以约720:1的比例由拉曼过程主导，且由于拉曼系数随声速v的-10次方缩放，发色团环境刚度提高约2倍可使T₁恢复至约100微秒，足以实现微摩尔级传感。纳摩尔级传感受限于直接过程的上限（79微秒），仅通过振动解耦无法突破该上限。我们获得了定量设计规则，确定光子产率是同等重要的瓶颈，并提出了一种用于化学特异性的频率分辨方案。
英文摘要
The demonstration that enhanced yellow fluorescent protein hosts an optically addressable spin-1 qubit in its metastable triplet state raises the prospect of genetically encoded quantum sensing at molecular length scales. We develop a detection-limit theory for using this fluorescent-protein spin qubit (FPSQ) to sense paramagnetic neural signaling radicals by spin relaxometry. We derive the transition-resolved Redfield relaxation matrix of the zero-field-split triplet coupled to a diffusing radical bath, establish the regime in which it collapses to a single exponential, and validate it against Lindblad simulations and nitrogen-vacancy benchmarks. Propagating the effects of photon shot noise, photobleaching-grounded photon budget, and finite measurement bandwidth, we find that the native room-temperature sensor falls short of physiological sensitivity by six to eight orders of magnitude with the bottleneck being the phonon-limited intrinsic $\Tone$. Analyzing the underlying direct and two-phonon Raman processes, we show that room-temperature relaxation is Raman-dominated by $\sim\!720\!:\!1$ and that, because the Raman coefficient scales as $v^{-10}$ with sound velocity, a $\sim\!2\times$ stiffening of the chromophore environment recovers $\Tone\sim\SI{100}{\micro\second}$, sufficient for micromolar sensing. Nanomolar sensing is obstructed by a direct-process ceiling of \SI{79}{\micro\second} that vibronic decoupling alone cannot breach. We obtain quantitative design rules, identify photon yield as a co-equal bottleneck, and propose a frequency-resolved protocol for chemical specificity.
