Cavity QED of electron spins in diamond

在量子通信网络中，信息由包含单个光子的光脉冲携带，并由单个量子系统或量子比特（如单个原子或单个电子自旋）进行处理。这种新的信息处理范式可以实现安全或牢不可破的通信，并可以解决传统计算机无法解决的计算问题。发展这种新范式的一个关键要求是在单光子和单量子比特的水平上控制光与量子系统之间的相互作用。这个实验项目使用薄金刚石膜中的单个电子自旋作为量子比特。通过将光子限制在小于50微米的光学微谐振腔中，实现了单光子与单自旋之间的强相互作用。主要目标是利用单个电子自旋来控制单个光子的量子态，从而实现可以在单光子水平上工作的光开关。这些交换机可以作为量子网络的重要组成部分。该研究项目还为研究生和本科生在纳米光子学和纳米制造以及量子科学与技术等领域提供了良好的培训机会。这种培训为学生在学术界、工业界或政府的职业生涯做准备。本项目开发了一种独特的复合腔QED系统，在该系统中，金刚石薄膜中的电子自旋通过共振拉曼跃迁与二氧化硅微谐振器中的光学低语廊模式的倏逝场耦合。在固体环境中探索了单电子自旋和单光子水平上的基本光学相互作用。研究活动主要集中在端-金比方案的实验演示上，该方案以原子的量子态为条件，实现了单光子的pi相移。这种腔QED过程发生在协同性（表征原子-光子或自旋-光子耦合强度的无量纲参数）超过1的极限下，但不需要单光子水平上的强耦合。近期目标是实现单自旋诱导的光学透明，并实现一种光子开关，可以通过与单个电子自旋的相互作用来控制单个光子的量子态。这些开关可以在量子网络中产生和分配量子纠缠，可能在量子信息技术的发展中发挥重要作用。

Non-Technical AbstractIn a quantum communication network, information is carried by light pulses containing single photons and is processed by individual quantum systems or quantum bits, such as single atoms or single electron spins. This new information processing paradigm can enable secure or unbreakable communication and can tackle computational problems that would otherwise be impossible with conventional computers. A key requirement for developing this new paradigm is the control of interactions between light and quantum systems at the level of single photons and single quantum bits. This experimental project uses individual electron spins in a thin diamond membrane as quantum bits. Strong interactions between single photons and single spins are enabled by confining the photons in an optical micro-resonator with a dimension less than 50 micrometers. The primary goal is to use a single electron spin to control the quantum state of a single photon, thus realizing an optical switch that can operate at the level of single photons. These switches can serve as an important component in a quantum network. This research project also provides excellent training opportunities for graduate and undergraduate students in areas including nanophotonics and nanofabrication as well as quantum science and technology. This training prepares the students for careers in academia, industry, or government.Technical AbstractThis project develops a unique composite cavity QED system, in which an electron spin in a thin diamond membrane couples to the evanescent field of an optical whispering gallery mode in a silica microresonator via a resonant Raman transition. Fundamental optical interactions at the level of single electron spins and single photons are explored in a solid state environment. The research activity focuses on the experimental demonstration of the Duan-Kimbe scheme, which realizes a pi-phase shift for a single photon, conditioned on the quantum state of an atom. This cavity QED process takes place in the limit that cooperativity, a dimensionless parameter characterizing the strength of atom-photon or spin-photon coupling, exceeds 1, but does not require strong coupling at the single-photon level. The near term objective is to achieve single-spin-induced optical transparency and to realize a photonic switch that can control the quantum state of a single photon through its interaction with a single electron spin. These switches can enable the generation and distribution of quantum entanglement in a quantum network, potentially playing a significant role in the development of quantum information technologies.