Characterizing and controlling optical and vibrational dynamics of single-photon emitting defects in hexagonal boron nitride

超声波敏感的量子传感器和牢不可破的量子密码技术使用单个光子(光粒子)或成对的光子来检测、编码、传输和检索量子信息。因此，可以按需产生和操纵单光子的材料对于部署用户友好的量子技术至关重要。本项目致力于寻找、表征和操纵六方氮化硼(HBN)中的单光子发射体。已知在hBN中存在单光子发射体系综，它们在室温下非常明亮和稳定。在这个项目中，将操纵晶体振动来提高单光子发射器的颜色纯度。这利用了这样一个事实：在室温下，hBN的晶体振动耦合到光子发射器，就像光和声音通过亚历山大·格雷厄姆·贝尔发现的光声效应耦合一样。该项目的成功将对量子设备技术产生革命性的影响，因为hBN发射器可以封装在与微电子和光纤通信兼容的芯片格式中。该项目将通过连接光学、材料和计算科学的多学科方法培训学生量子信息科学。范德比尔特科学推广中心和教学中心建立的外联计划将使项目团队做好准备，访问纳什维尔市学校和邻近未得到充分服务的县的初中和高中班级，以激励和鼓励未来在量子科学和技术方面的研究和工作。一个多元化、包容性的研究团队将与已有数十年历史的博士桥项目合作，将历史悠久的黑菲斯克大学的学生与范德比尔特大学的研究小组联系起来。技术说明。基于光的可扩展量子技术需要具有良好特性、可控制的固态单光子发射器，可以根据需要进行操纵和纠缠。六方氮化硼(HBN)中的晶体缺陷集具有一系列有用的性质：超高亮度、窄线宽和室温下的光稳定性，以及在中红外具有异常大的光子态密度的双曲声子极化电子。然而，量子发射器频率(可见光和近红外)和双曲极化和声子频率(中红外)之间的光谱失配很大，使得同时开发所有这些理想的特性变得困难。该项目将利用hBN中的高声子态密度来控制单光子发射，并通过声子边带的反斯托克斯泵浦来提高光谱纯度。利用光谱和时间分辨近场光谱和显微镜，通过光致发光、纳米傅里叶变换红外光谱和光子关联研究，识别和表征单层和几层hBN薄片中的单个单光子发射体；利用中红外波段的纳米光学扫描探针显微镜，确定发射态的电子性质和与其耦合的振动相互作用；通过泵浦反斯托克斯光子模，演示通过局部改变发射体的介电环境来主动控制发射体的寿命和频率；以及探索声子-发射体耦合和局部应变对同一BN片上两个发射体之间的光谱纯度和光子纠缠的影响。通过表征hBN中的单个量子发射体并展示可控纠缠，该项目开辟了一条通往平面室温器件的变革性途径，用于量子加密、计算和传感，其外形系数本质上可以适应芯片上的几何结构和光纤耦合。这些实验将解决长期存在的关于hBN中基于缺陷的单光子发射体物理性质的不确定性，使人们能够更深入地了解发射和纠缠背后的物理机制。通过反斯托克斯机制和在hBN单片中控制应变梯度来控制光子纯度，也可以通过将应变机制和电子-声子耦合与单量子发射的电子过程分开来增强光子纠缠的稳定性。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Description.Ultrasensitive quantum sensors and unbreakable quantum cryptography technologies use single photons (particles of light) or pairs of photons to detect, encode, transmit and retrieve quantum information. Hence materials in which single photons can be generated and manipulated on demand are essential to deploying user-friendly quantum technologies. This project focuses on finding, characterizing and manipulating single-photon emitters in hexagonal boron nitride (hBN). Ensembles of single-photon emitters are known to exist in hBN, and they are extremely bright and stable at room temperature. Crystal vibrations will be manipulated in this project to improve the color purity of the single-photon emitters. This take advantage of the fact that crystal vibrations of hBN couple to the photon emitters at room temperature just as light and sound are coupled through the photoacoustic effect discovered by Alexander Graham Bell. Success in this project will have a transformative impact on quantum-device technologies because hBN emitters can be packaged in an on-chip format that is compatible with microelectronics and fiber-optic communications. The project will train students in quantum information sciences through a multi-disciplinary approach that connects optics, materials and computational science. Established outreach programs at Vanderbilt’s Center for Science Outreach and Center for Teaching will prepare the project team to visit middle- and high-school classes in Nashville city schools and underserved neighboring counties, to inspire and encourage future study and work in quantum science and technology. A diverse, inclusive research team will be built in partnership with the decades-old Bridge-to-Ph.D. program connecting students from Historically Black Fisk University to Vanderbilt research groups.Technical Description.Scalable quantum technologies based on light require well-characterized, controllable solid-state, single-photon emitters that can be manipulated and entangled on demand. Ensembles of crystal defects in hexagonal boron nitride (hBN) host single-photon emitters with a constellation of useful properties: ultra-high brightness, narrow linewidth, and photostability at room temperature, and hyperbolic phonon polaritons with an exceptionally large photon density of states in the mid-infrared are also supported in hBN. However, the large spectral mismatch between quantum-emitter frequencies (visible vs near-infrared) and hyperbolic-polariton and phonon frequencies (mid-infrared) makes it difficult to exploit all of these desirable properties simultaneously. This project will capitalize on the high phonon density of states in hBN to control single-photon emission and increase spectral purity by anti-Stokes pumping of phonon sidebands. Spectrally and temporally resolved near-field spectroscopy and microscopy will be deployed to identify and characterize individual single-photon emitters in mono- and few-layer hBN flakes by photoluminescence, nano Fourier-transform infrared spectrometry and photon-correlation studies; determine electronic properties of emitting states and the vibrational interactions that couple to them using nano-optical scanning probe microscopy in the mid-infrared; demonstrate active control of emitter lifetime and frequency by locally varying the dielectric environment of the emitter by pumping anti-Stokes photon modes; and explore the effects of phonon-emitter coupling and local strain on spectral purity and photon entanglement between two emitters on the same hBN flake. By characterizing individual single-quantum emitters in hBN and demonstrating controlled entanglement, the project opens a transformative path to planar, room-temperature devices for quantum cryptography, computation and sensing in a form factor intrinsically adaptable to on-chip geometries and optical-fiber coupling. These experiments will resolve long-standing uncertainties about the physical properties of the defect-based single-photon emitters in hBN, enabling a deeper understanding of the physical mechanisms underlying emission and entanglement. Controlling photon purity through the anti-Stokes mechanism and controlled strain gradients in single flakes of hBN may also enhance the stability of photon entanglement by separating the strain mechanism and electron-phonon coupling from the electronic process of single-quantum emission.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.