Stoichiometric rare-earth crystals for novel integrated quantum memories

用于新型集成量子存储器的化学计量稀土晶体

• 批准号: EP/V002902/1
• 负责人: Margherita Mazzera
• 金额: $ 48.32万
• 依托单位: Heriot-Watt University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FV002902%2F1
• 关键词: Stoichiometric; rare; earth; crystals; novel

Quantum information science is the field of research that studies the information present in a quantum system. A number of new technological applications can be envisaged thanks to exquisitely quantum phenomena. While classical information encoding relies on bits, which can be either 0s and 1s, the quantum bits (or qubits) are associated to the state of quantum objects, e.g. single atoms, single spins, or single photons. Because of the quantum superposition principle, the qubits can then be 0s, 1s, or coherent superposition of both, thus giving access to an exceptionally richer alphabet. Quantum information science also exploits quantum entanglement, i.e. strong correlation between quantum objects, as a resource for fast and secure quantum communication protocols.In view of realising networks for quantum communication, quantum memories are fundamental devices as they act as interfaces between the photons, used as information carriers, and atoms, exploited for information storage and processing. To be useful in quantum networks, the quantum memories must fulfil specific requirements, as on-demand read-out, high efficiency and fidelity, long storage time, and multimodality. While atomic gases enabled the first remarkable quantum storage experiments, solid-state systems also offer interesting perspectives.Among these, the rare-earth doped crystals recently emerged as attractive candidates because they are ensembles of optically active ions naturally trapped in inert media, which do not require external trapping fields and ultra-high vacuum chambers. They have already featured performances equalising or overcoming those of trapped atoms or cold atomic ensembles in terms of efficiency and storage times. These crystals exhibit transitions both in the optical and in the radio- and micro-wave range, thus they could serve as photonic or microwave memories, but also as interfaces between optical and microwave frequencies, thus opening the way to hybrid systems employing superconducting devices.Despite their very promising performances and the milestone experiments realised in the last decade, a unique rare-earth doped crystal that fulfils all the requirements of an ideal photonic quantum memory does not yet exist.This project exactly tackles this problem and aims at developing a novel platform for telecom-compatible integrated quantum devices, containing solid-state quantum memories with unprecedented functionalities. The central idea is to employ not rare-earth doped crystals but stoichiometric crystals, i.e. where the rare-earth ions fully substitute one element of the crystal matrix, with the two-fold aim of increasing the absorption of light and narrowing the inhomogeneous linewidth of the electronic transitions, thanks to a lower local mechanical stress.The challenges addressed are:- the optimisation of the coherence properties of bulk crystals that will enable the implementation of quantum storage protocols, never demonstrated in these kind of materials; - the exploration of confined environment, i.e. laser written waveguides, for the realisation of integrated quantum memories.We expect the waveguide fabrication to facilitate the realisation of fibre-coupled devices and the efficient manipulation of the atomic transitions by means of electric fields, and to boost the interaction strength between the light and the rare-earth ions. This might give access to the storage of telecom light exploiting optical transitions that in diluted bulk samples would be too weak. Therefore, the proposed platform might permit the simultaneous demonstration of efficient, long-lived and multiplexed storage devices, which are also compatible with existing telecom fibre network. Such quantum memories would outperform the existing quantum storage devices, and their demonstration would open new avenues for the use of solid-state technologies for real quantum information applications.

量子信息科学是研究量子系统中存在的信息的研究领域。由于精致的量子现象，可以设想许多新技术应用。虽然经典信息编码依赖于位（可以是 0 和 1），但量子位（或量子位）与量子对象的状态相关联，例如单个原子、单个自旋或单个光子。由于量子叠加原理，量子位可以是 0、1 或两者的相干叠加，从而获得异常丰富的字母表。量子信息科学还利用量子纠缠，即量子物体之间的强相关性，作为快速、安全的量子通信协议的资源。考虑到实现量子通信网络，量子存储器是基本设备，因为它们充当光子之间的接口，用于作为信息载体和原子，用于信息存储和处理。为了在量子网络中发挥作用，量子存储器必须满足特定的要求，如按需读出、高效率和保真度、长存储时间和多模态。虽然原子气体实现了第一个引人注目的量子存储实验，但固态系统也提供了有趣的前景。其中，稀土掺杂晶体最近成为有吸引力的候选者，因为它们是自然捕获在惰性介质中的光学活性离子的集合，这使得不需要外部捕获场和超高真空室。它们在效率和存储时间方面的性能已经达到或超过了捕获原子或冷原子系综的性能。这些晶体在光学、无线电和微波范围内表现出跃迁，因此它们可以用作光子或微波存储器，也可以用作光学和微波频率之间的接口，从而为采用超导器件的混合系统开辟了道路。尽管它们的性能非常有前途，并且在过去十年中实现了里程碑式的实验，但满足理想光子量子存储器所有要求的独特稀土掺杂晶体尚不存在。该项目正是解决了这个问题，旨在开发一种新颖的稀土掺杂晶体。平台电信兼容的集成量子设备，包含具有前所未有的功能的固态量子存储器。中心思想是不采用稀土掺杂晶体，而是采用化学计量晶体，即稀土离子完全取代晶体基质的一种元素，具有增加光吸收和缩小不均匀线宽的双重目的。由于局部机械应力较低，电子跃迁得以实现。所面临的挑战是： - 优化块状晶体的相干特性，这将能够实现量子存储协议，而这在此类材料中从未得到证实； - 探索受限环境，即激光写入波导，以实现集成量子存储器。我们期望波导制造能够促进光纤耦合器件的实现以及通过电场有效操纵原子跃迁，并增强光与稀土离子之间的相互作用强度。这可能允许利用光跃迁来存储电信光，而在稀释的散装样品中这种光跃迁太弱了。因此，所提出的平台可能允许同时演示高效、长寿命和多路复用的存储设备，这些设备也与现有的电信光纤网络兼容。这种量子存储器的性能将优于现有的量子存储设备，它们的演示将为将固态技术用于真正的量子信息应用开辟新的途径。