二維材料系統(tǒng)可實現(xiàn)單光子發(fā)射器和自旋量子比特，為新型量子現(xiàn)象和技術(shù)應(yīng)用開辟了一個嶄新的舞臺。例如，二維六方氮化硼結(jié)構(gòu)可容納穩(wěn)定的單光子發(fā)射器和自旋三重態(tài)缺陷結(jié)構(gòu)，因而引起了人民的廣泛關(guān)注。

然而，這些量子缺陷的不可控性及化學(xué)性質(zhì)的不確定性阻礙了其進一步發(fā)展。通過引入能精確調(diào)控的外部缺陷，可以彌補量子缺陷化學(xué)性質(zhì)的不確定性問題。

來自美國加州大學(xué)戴維斯分校物理系的Ping Yuan教授，提出了一套完整的理論框架來識別寬帶隙二維材料系統(tǒng)中的量子缺陷，可用于單光子發(fā)射體和自旋比特的設(shè)計。他們通過用第一性原理方法計算了h-BN材料系統(tǒng)的缺陷能量，確定了具有三重態(tài)的缺陷結(jié)構(gòu)，通過分析次級量子自旋的零場分裂，對相關(guān)能級進行了控制。

此外，根據(jù)缺陷躍遷和輻射壽命，他們篩選出了h-BN中潛在的單光子發(fā)射器缺陷結(jié)構(gòu)。該理論框架考慮了缺陷-激子耦合等多體相互作用，并計算了每個缺陷的電子結(jié)構(gòu)和光譜。通過考慮Huang-Rhys近似之外的聲子波函數(shù)重疊，作者開發(fā)了一種計算非輻射系統(tǒng)間交叉速率的方法。這項工作為二維材料中缺陷設(shè)計提供了一套完整的第一性原理理論框架，并為二維材料在量子信息科學(xué)中的應(yīng)用提供了參考。

該文近期發(fā)表于npj Computational Materials 7： 59 （2021），英文標題與摘要如下。

Despite the recognition of two-dimensional （2D） systems as emerging and scalable host materials of single-photon emitters or spin qubits， the uncontrolled， and undetermined chemical nature of these quantum defects has been a roadblock to further development. Leveraging the design of extrinsic defects can circumvent these persistent issues and provide an ultimate solution.

Here， we established a complete theoretical framework to accurately and systematically design quantum defects in wide-bandgap 2D systems. With this approach， essential static and dynamical properties are equally considered for spin qubit discovery.

In particular， many-body interactions such as defect–exciton couplings are vital for describing excited state properties of defects in ultrathin 2D systems. Meanwhile， nonradiative processes such as phonon-assisted decay and intersystem crossing rates require careful evaluation， which competes together with radiative processes.

From a thorough screening of defects based on first-principles calculations， we identify promising single-photon emitters such as SiVV and spin qubits such as TiVV and MoVV in hexagonal boron nitride. This work provided a complete first-principles theoretical framework for defect design in 2D materials.

編輯：jq