金刚石纳柱腔NV色心密集量子点群的超荧光量子相干光源研究

There is a pressing need of the quantum optical source with high intensity, long coherence time, and high fidelity or degree of coherence for the application of Quantum information. Superfluorescence (SF) is the cooperative coherent emission from a dense quantum system in population inversion after an initial coherent ensemble formed under the interactions of electro-magnetic fields. The quantum system of diamond nitrogen-vacancy centers contains series of quantum optical merits including long decoherence time, excellent homogeneity, and ground states spin manipulations, and so on, which satisfies the prerequisites of the excitation of superfluorescence. By preparation of high density and homogeneity of NV centers in the diamond nano-rod cavities with transverse quantum confinement effects, this project aim to research on the characteristics of the initiation of macroscopic polarization, population inversion, carrier transitions, and dipole interactions that lead to the decoherences of the quantum optical system, under the conditions of liquid helium temperature, and coherent manipulations on the quantum system by pico-second pulse lasers and Stark pulse electric fields through non-resonant, quasi-resonant, and resonant excitations. Finally to develop a prototype device which combines the quantum optical properties of the diamond NV system together with the characteristics of superfluorescence excitation, which is expected to have major applications in the fields of quantum information, remote sensing, and imaging in the future. Providing a new technical approach for the extension of the solid state quantum optical system, and lay a scientific foundation for the realization of the basic quantum information functions including high pulse intensity, and longtime quantum coherent optical emission and transmission, and so on.

量子信息技术亟需高强度、长退相干、高相干度或保真度的量子光源。超荧光是密集量子体系在电磁场作用下形成宏观极化和布居数反转产生的合作相干发光。金刚石氮原子-空穴（NV）量子体系具有长退相干时间、优良均匀性、基态自旋操作等量子光学特性，满足超荧光激发的必要条件。本项目通过在具有横向量子限制效应的金刚石纳柱腔内制备高密度、高均匀度的NV色心量子点群，研究液氦低温、皮秒脉冲激光与Stark脉冲电场调控下量子系统在非共振、准共振和共振激发下的宏观极化形成、布居数反转、能级跃迁、和偶极相互作用导致的退相干等特征，获得产生超荧光激发的量子点材料与量子相干调控边界条件。研制出融合了该量子体系量子光学特性和超荧光激发特征的原型器件，未来在量子信息、遥感和成像等领域可望获得重大应用。为固态量子体系的扩展性提供新的技术途径，为实现高脉冲强度、长退相干时间的量子相干光发射和传输等基本量子信息功能奠定科学基础。

量子信息技术亟需高强度、长退相干、高相干度或保真度的量子光源，基于这样的研究背景，我们提出了在金刚石纳柱腔结构上制备超荧光量子光源的研究方案。工作分别从量子调控理论、纳柱腔设计与制备、纳柱腔中NV色心荧光测试三个方面展开。首先研究了金刚石NV色心单个量子点的绝热捷径量子调控理论，并基于FDTD方法分析了金刚石纳柱腔结构的腔模式、量子限制效应等对腔内量子点荧光光场的横向限制效应。基于计算结果，形成了对金刚石纳柱腔结构和尺寸的设计方案。选择了曲面锥形柱腔结构（底径：顶径=5:2，顶端曲面）。从多体哈密顿函数中推导出非线性两原子主方程描述量子点和辐射场。将时间演化算符应用于Schwinger–Keldysh 图，采用马尔科夫近似，推算出NV色心量子体系的自发衰减率和泵浦率、能级布居数反转速率和超荧光的加速率和衰减率。进一步地研究了自发辐射对量子绝热捷径调控的影响。结果表明，在强耗散区域，自发辐射反而能有效增强量子效率，从而揭示了在NV色心密集量子点群荧光场作用下，能够实现量子效率的增强，实现多量子点的合作激发。基于表面电场调控的NV色心量子点荧光研究证实了这个推论。我们实验制备出各方面参数都非常接近设计方案的金刚石纳柱腔，NV色心密度可达到平均约1/1000nm^3。分别在室温和低温条件下测试了纳柱腔中密集NV色心点群在皮秒激光器激发下的自发辐射效果。本研究有望解决现有量子光源面临的主要问题，实现量子光源的单片阵列化、集成化等。未来有望应用于量子信息技术的多个领域。我们在本项目中的研究工作为开发高强度、长退相干、稳定的量子光源提供了理论和实验依据。