量子存储研究进展

量子技术,比如量子通信、量子计算,具有经典技术所不具有的优势.但是,作为量子技术基本元素的量子态往往极为脆弱,很容易受到外界环境的影响而丢失,而且量子态的制造和量子操作往往是概率性的.这种概率性使得远距离量子通信和大规模的量子计算很难实现,除非有量子存储器将这些随机产生的量子态缓存并同步起来.在过去的十几年中,量子存储在各种各样的存储方案中得到了研究,而且已经从最初的原理性演示逐步发展到了如今的近乎可实用化.现如今,量子存储领域追求的是可实用化,而判断一个存储器是否可以实用化的基本标准是:高存储效率、低噪音、长寿命(或者大的时间带宽积)和室温条件下运行.通过介绍多个具有代表性的存储方案,本文给出了量子存储领域的研究现状和发展趋势.其中基于室温原子系综的宽带量子存储因其装置简单、实用性更强而广受关注.但是由于噪音问题,直到最近才在实验室中实现可工作在室温环境中的宽带FORD (far off-resonance Duan-Lukin-Cirac-Zoller)量子存储和梯形量子存储.本文对多种存储方案的工作原理、优缺点进行了介绍,对FORD方案之所以能够成功进行了分析,还对量子存储的降噪方法进行了总结.

Research progress of quantum memory

Quantum technologies, for example, quantum communication and quantum computation, promise spectacular quantum enhanced advantages beyond what can be done classically. However, quantum states, as the element of quantum technologies, are very fragile and easily get lost to the environment, and meanwhile, their generation and quantum operations are mostly probabilistic. These problems make it exponentially hard to build long-distance quantum channels for quantum communication and large quantum systems for quantum computing. Quantum memory allows quantum states to be stored and retrieved in a programmable fashion, therefore providing an elegant solution to the probabilistic nature and associated limitation by coordinating asynchronous events. In the past decades, enormous advances in quantum memory have been made by developing various storage protocols and their physical implementations, and the quantum memory has gradually evolved from the initial conceptual demonstration to a nearly practical one. Aiming at being practicable for efficient synchronisation and physical scalability, an ideal quantum memory should meet several key features known as high efficiency, low noise level, large time bandwidth product (lifetime divided by pulse duration) and operating at room temperature. Here, we present the research status and development trends of this field by introducing some typical storage protocols. Among these protocols, a room-temperature broadband quantum memory is the most attractive due to its simplicity and practicability. However, at room temperature, noise becomes dominant and is a bottleneck problem that has impeded the realization of a real room-temperature broadband quantum memory in the last decades. Recently, the noise problem has been solved in two memory protocols, i.e. FORD (far off-resonance Duan-Lukin-Cirac-Zoller) protocol and ORCA (off-resonant cascaded absorption) protocol. In this paper, the working principles, the merits and demerits of various quantum memory protocols are illustrated. Furthermore, the approaches to eliminating noise and the applications of quantum memory are summarized.