High Efficiency Multimode Quantum Memory Using Atomic Frequency Combs in an Optical Cavity

忠实地存储和检索量子态的量子存储器是远程量子通信中量子中继器的基本组成部分。在现有的实现量子存储器的方法中，稀土系综中的原子频率梳（AFC）被认为具有突出的潜力，包括高达100%的存储效率、高保真度、长达数秒的存储时间、高达千兆比特/秒的高比特率的大时间带宽产品、多模式容量、大范围的工作波长，以及使用现成组件相对简单的设置是固态的。实现高效率是充分发挥其潜力的基石。目前，阻碍最佳效率的两个主要障碍是AFC的低吸收长度和不良形成的光谱和空间结构。在这个NSF支持的项目中，结合了两种新颖的方案来解决这些问题：使用低精细度的光腔来增加吸收长度，以及使用各种时间、光谱和空间配置来优化AFC结构。主要的工作将集中在理解物理和开发关键的使能技术，以制备稀土集成和存储/检索过程中的AFC。我们计划使用铥离子掺杂晶体作为原型材料来开发和测试这些方案。所得到的方法和技术有望应用于类似的稀土系综。支持的项目将对推进量子信息科学与技术产生广泛影响。该项目旨在将量子存储器向实际设备的巨大进步，这将在远程量子通信和分布式量子计算中找到应用。这项研究还将有助于更好地理解量子理论，如退相干、纠缠和量子不可克隆定理。教育是这个项目的重要组成部分。这些努力的重点是培养量子信息相关领域的新一代科学家和工程师，并为科学劳动力的多样性做出贡献。在线量子力学课程将为高中科学教师开发，以便我们的K-12学校系统将更好地准备向年轻的学生介绍量子概念。通过将量子信息前沿的新发展引入现有的量子力学课程，并为学生提供项目研究机会，将本科生和研究生招募到该领域。

Quantum memory that faithfully stores and retrieve quantum states is a basic building block for quantum repeaters in long-distance quantum communication. Among the existing approaches to implementing quantum memories, the atomic frequency comb (AFC) in rare-earth ensemble is identified for its outstanding potential, which includes memory efficiency up to 100%, high fidelity, long storage times up to seconds, a large time-bandwidth product for a high bit rate up to gigabit/s, multi-mode capacity, a large range of operational wavelengths, and being solid-state with a relatively simple setup using off-the-shelf components. Achieving high efficiency is the corner stone to fully realize theis potential. Currently, the two major obstacles preventing optimal efficiency are the low absorption length and poorly-formed spectral and spatial structures in the AFC. In this NSF supported project, two novel schemes are combined to solve the problems: employing a low finesse optical cavity to boost the absorption length, and using various temporal, spectral and spatial configurations to optimize the AFC structure. The main efforts will focus on understanding the physics and developing critical enabling techniques in preparing the AFC in rare-earth ensembles and in the storage/retrieving process. We plan to use thulium ions doped crystals as prototype materials to develop and test the schemes. The resulting methods and techniques are expected to be applicable to similar rare-earth ensembles.The supported project will have broad impact in advancing quantum information science and technology. The project aims at great advances in quantum memories towards practical devices, which will find applications in both long-distance quantum communication and distributed quantum computation. The investigation will also lead to better understanding of quantum theory, such as decoherence, entanglement, and quantum no-cloning theorem. Education is an important component in this project. The efforts focus on cultivating a new generation of scientists and engineers in quantum information-related fields and contributing to the diversity of the scientific workforce. An on-line quantum mechanics course will be developed for high school science teachers so that our K-12 school system will be better prepared to introduce quantum concepts to students at young age. Undergraduate and graduate students will be recruited to the field by introducing new developments in the quantum information frontier into existing quantum mechanics courses, and by providing students research opportunities in the project.