APPLICATION
SRS射頻信號(hào)發(fā)生器在金剛石氮空位色心的研究介紹
量子計(jì)算和量子傳感近年來(lái)受到了廣泛的關(guān)注.金剛石氮空位色心以其簡(jiǎn)單穩(wěn)定的自旋能級(jí)結(jié)構(gòu)、高效便捷的光學(xué)躍遷規(guī)則以及室溫下超長(zhǎng)的自旋量子態(tài)相干時(shí)間而成為量子信息科學(xué)中引人矚目的新星,近十年來(lái),金剛石氮空位色心的研究呈爆炸式增長(zhǎng)(見(jiàn)圖1)
圖1:每年提及“氮空位”和“金剛石”的出版物總數(shù)(Google Scholar)。
顧名思義,氮空位色心(NV-Nitrogen-Vacancy center)(圖2)是由一個(gè)氮原子取代金剛石中的一個(gè)碳原子,然后捕獲周?chē)囊粋€(gè)空穴形成的。在NV位上懸浮鍵的電子通過(guò)雜化產(chǎn)生自旋-1系統(tǒng),具有明確的能量狀態(tài)和較長(zhǎng)的自旋壽命,即使在室溫下也是如此。這樣就可以通過(guò)磁共振的自旋操控技術(shù)在精確定時(shí)的微波磁場(chǎng)下來(lái)控制NV點(diǎn)的自旋狀態(tài)。由于它的能級(jí)對(duì)外部磁場(chǎng)和電場(chǎng)都很敏感,使得這種自旋狀態(tài)可以作為外部環(huán)境的傳感器。
圖2:金剛石中NV色心由碳原子(灰色)、氮原子(橙色)和相鄰空位組成,并有懸空鍵(紫色)[1]。
在NV實(shí)驗(yàn)中監(jiān)測(cè)到的能量狀態(tài)如圖3所示:
眾所周知,金剛石中的缺陷會(huì)使原本透明的晶體產(chǎn)生顏色(例如,氮取代缺陷使金剛石呈現(xiàn)黃色,而硼取代則產(chǎn)生藍(lán)色)。在532nm激光激發(fā)下,NV在637 nm處產(chǎn)生熒光衰減。重要的是?s=±1自旋態(tài)是無(wú)輻射衰減,從而提供了一種利用監(jiān)測(cè)光致發(fā)光變化來(lái)檢測(cè)自旋狀態(tài)的方法。也就說(shuō),當(dāng)自旋態(tài)被激發(fā)到不穩(wěn)定態(tài)?s =±1級(jí)(使用2.87 GHz微波),有缺陷的紅光輸出會(huì)略有減少(圖4 (a))。此外,?s =±1的能級(jí)狀態(tài)可以被外部磁場(chǎng)調(diào)節(jié)。通過(guò)測(cè)量吸收峰之間的頻率分裂(如圖4(b)所示),可以測(cè)量出該外部磁場(chǎng)。
圖4。(a)在2.87GHz躍遷共振微波作用下的光致發(fā)光衰減(??= 0和1狀態(tài)之間)。
(b)非零磁場(chǎng)下的??= +1和-1狀態(tài)之間的分裂[3]。
能量狀態(tài)的改變也可能是由外部電場(chǎng)[4],溫度[5] [6]或金剛石晶格的應(yīng)變[7]引起,這使得NV光學(xué)探測(cè)磁共振(ODMR)對(duì)于感測(cè)這些量中的任何一個(gè)都有作用。因?yàn)镹V軸可以匹配金剛石晶格中4個(gè)晶軸中的任何一個(gè),因此可以執(zhí)行3D矢量場(chǎng)感測(cè)[8]。例如,結(jié)合共聚焦顯微鏡技術(shù)可以解決NV共振位移的空間分辨圖,趨磁細(xì)菌產(chǎn)生的磁場(chǎng)矢量圖譜詳見(jiàn)(圖5)[g]。
圖5。(a)趨磁細(xì)菌的光學(xué)圖像。(e)同一細(xì)菌的SEM圖像,其中磁性納米粒子(黑色)清晰可見(jiàn)。(b,c,d)磁場(chǎng)x, y, z分量由NV金剛石光學(xué)探測(cè)磁共振測(cè)量確定。(f,g,h)實(shí)測(cè)場(chǎng)分布的數(shù)值擬合(來(lái)自[g])。
和大多數(shù)磁共振測(cè)量一樣,第一次NV實(shí)驗(yàn)涉及大量的缺陷。然而,令人驚訝的是,在低缺陷密度的樣品中,單個(gè)NV色心可以被隔離和監(jiān)測(cè)。由于NV是原子大小的,這意味著單自旋NV傳感器的空間分辨率僅受限于與其感興趣樣品的距離。例如,通過(guò)在原子力顯微鏡探針的尖端定位單個(gè)NV色心,已經(jīng)證明了具有25nm分辨率和56nT/Hz-1/2的磁疇成像[10]。
此外,NV色心的極端敏感性和生物相容性(金剛石只是碳,因此沒(méi)有表現(xiàn)出毒性),顯示了納米核磁共振測(cè)量的特殊前景,其中NV中心被耦合到與之感興趣的有機(jī)和生物分子的核自旋的雜散場(chǎng)上[11]。因此,NV被定位為革命性的納米磁共振成像技術(shù),并提供了一種在環(huán)境條件下獲得單分子3D圖像的途徑[12]。事實(shí)上,NV色心的單質(zhì)子自旋探測(cè)已經(jīng)被證實(shí)[13]。
NV場(chǎng)感測(cè)和納米成像不限于靜態(tài)場(chǎng)?,F(xiàn)在,一些研究小組已經(jīng)證明了基于NV探測(cè)和時(shí)變磁場(chǎng)的磁場(chǎng)掃描是由鐵磁鐵中的自旋波產(chǎn)生[14][15]或電流波動(dòng)[16][17]。
為了進(jìn)一步增加NV應(yīng)用的長(zhǎng)列表、長(zhǎng)壽命的自旋狀態(tài)、與外部場(chǎng)的可操作性以及與環(huán)境的可調(diào)諧相互作用(通過(guò)晶格工程)也使它們成為量子計(jì)算中信息單元“qubit”的領(lǐng)跑者[18]
量子計(jì)算和傳統(tǒng)計(jì)算一樣,可能需要將長(zhǎng)壽命存儲(chǔ)位與快速處理位分離。將長(zhǎng)壽命的“內(nèi)存”量子位(基于附近的氮原子或13c原子核自旋)與NV自旋的耦合[19][20][21]可以精確地提供這種內(nèi)存和處理架構(gòu)。超導(dǎo)磁通量子位(另一個(gè)強(qiáng)大的量子計(jì)算候選者)和NV色心之間的相干耦合也得到了證明[22],為量子處理和存儲(chǔ)所需要的光學(xué)與微波之間讀寫(xiě)的接口鋪平了道路。
SRS產(chǎn)品在NV研究中的應(yīng)用
在NV金剛石中進(jìn)行光學(xué)檢測(cè)磁共振實(shí)驗(yàn)的關(guān)鍵是掃描微波頻率的能力。為了測(cè)量自旋態(tài)壽命,執(zhí)行微波脈沖序列也很有用。SRS射頻信號(hào)發(fā)生器(SG384和SG386)和矢量信號(hào)發(fā)生器(SG394和SG396)非常適合在NV-ODMR研究中的所需要的頻率范圍內(nèi)產(chǎn)生微波。下面是使用SRS產(chǎn)品的NV相關(guān)參考的列表。
1. Optical magnetic imaging of living cells
https://www.nature.com/articles/nature12072
使用設(shè)備: SG384 (+ amplifier)
2. Miniature Cavity-Enhanced Diamond Magnetometer
https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.8.044019
使用設(shè)備: SG394 (+ 16W amplifier, circulator)
3. Microwave-free magnetometry with nitrogen-vacancy centers in diamond
https://aip.scitation.org/doi/full/10.1063/1.4960171
使用設(shè)備: SR865, SIM960
4. Precision temperature sensing in the presence of magnetic field noise and vice-versa using
nitrogen-vacancy centers in diamond
https://arxiv.org/abs/1802.07224
使用設(shè)備: SG394(2x) (+power combiner, switch, and amplifier), SR850
5. Quantum Control of Nuclear Spins Coupled to Nitrogen-Vacancy Centers in Diamond
(dissertation, S. Sangtawesin)
使用設(shè)備: SG394 (+ amplifier)
References
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