鑽石發光中心量子自旋弛豫之研究

本文專注於探討螢光奈米鑽石氮空缺顏色中心的基態電子三重態的內自旋弛豫物理。我們測量受近共振微波場作用下，自旋由完全偏極化在ms = 0次能階態的起始條件，弛豫至完全非偏極化，即平均分布於ms = 0, ±1的時間長度，並探討自旋弛豫與外加微波場之間的關係。在實驗數據分析中，我們先以直觀的指數衰減擬合數據，得出自旋弛豫時間與微波頻率及微波強度的關係、並將擬合得出的弛豫時間對微波頻率做圖，得出光檢弛豫譜。而本領域常用的光檢磁共振法則是用於測量至的躍遷頻率，是為~2.87 GHz。在外加微波場達到共振條件下，螢光奈米鑽石的亮度只低了近10%。但在微波達到共振條件下，自旋弛豫時間則可以遠小於內秉的縱向弛豫時間或T1，取決於微波功率。我們發現光檢弛豫譜與光檢磁共振譜高度相似，但弛豫譜的高低值對比度遠大於磁共振譜。接著，我們將數據以更精緻的三能階理論數值模擬擬合，從無外加微波場的弛豫數據擬合得出螢光奈米鑽石的內秉縱向弛豫時間，T1 ~1290 μs。我們也以擬合得出不同微波功率的拉比頻率，並得出在本實驗條件下，微波功率0.2 – 6 mW產生的拉比頻率為0.05 – 0.14 MHz。將來我們或許可以利用測量奈米鑽石內自旋弛豫時間的原理，發展出奈米尺度的微波頻率及微波功率感測元件。

關鍵字

螢光奈米鑽石；氮空缺色心；自旋弛豫；三能階原子；光檢磁共振；光檢弛豫譜；奈米微波感測器

並列摘要

In this thesis, we study spin relaxation of ground electronic triplet states in nitrogen-vacancy color center in fluorescent nanodiamond (FND). We measured the relaxation time from the ms = 0 state to equal distribution in the ms = 0, ±1 states, under the influence of a near-resonant microwave field. In data analyses, we first fitted the experimental data to single-exponential decay, from which we determined the relaxation time vs. the frequency and power of the applied microwaves. By plotting the relaxation time vs. microwave frequency, we constructed a relaxation spectrum, with a spectral shape close to that of the spin resonance spectrum. The spin resonance for and transition is ~2.87 GHz, which is commonly determined by optically detected magnetic resonance (ODMR) method, we thus coin our new method the optically detected relaxation spectroscopy (ODRS). In the resonance condition, the brightness of an FND is reduced by 10%, while the spin relaxation time can be much shorter than the intrinsic longitudinal relaxation time, T1, depending on the microwave power. Thus the ODRS gives a spectrum with a much higher contrast than that of an ODMR spectrum. Finally, we fitted our data to a 3-level atom model, from which we determined T1 ~1290 μs. We further fitted the data to determine the Rabi frequencies which are 0.05 - 0.14 MHz for microwave powers 0.2 – 6 mW. In the future, we may can develop a nano-sensor for determining the frequency and power of a microwave utilizing spin relaxation in FND.