Towards Real Applications in Broadband Quantum Memories

想象一张无法伪造的钞票，因为每当有人试图读取它时，序列号都会被扰乱。但如果你是银行家，你可以读这本书。听起来像哈利波特吗？想象一下，一台计算机通过一次模拟所有可能的化学反应来预测药物的行为！这不是菲利普·普尔曼关于平行宇宙的幻想中的想法。像这样的真正技术就在眼前。这是量子物理学中令人着迷的、反直觉的世界。在过去的几十年里，通信和计算技术的巨大进步使这个时代进入了信息时代，并比工业革命更彻底地改变了人们的生活和互动方式。这些进步得益于半导体晶体管和激光等设备的发展，如果没有量子物理的奇怪特性，这些设备是不可能实现的。但是，尽管现代计算机已经远远超过了穿孔卡和真空管阀门等早期技术，但在根本的概念层面上，它们仍然使用完全相同的信息类型--0和1的字符串称为位。量子物理学将让我们远远超越这一点，进入量子信息的奇怪世界，在那里，“量子比特”可以同时为0和1！能够处理这类信息的计算机在执行困难的模拟或破解代码方面会以指数级的速度增长。使用量子信息进行通信可以做到“防窃听”--完全安全。在过去的十年里，一项巨大的研究努力将这些非凡的技术从抽象的想法带入了小规模的实验。建造量子计算机最有希望的方法之一是基于被称为光子的单个光粒子，这种粒子可以通过光纤远距离传输，并通过普通的透镜和镜子进行操纵。但与普通计算机一样，量子计算机需要内存来同步计算的不同部分，方法是存储量子信息，直到需要它为止。因此，要建造一台光子量子计算机，我们还需要有一个可以存储单光子的量子存储器。困难的是，这些特殊的存储器需要能够存储脆弱的量子信息，而不破坏它，甚至不破坏它(测量它)。在这个项目中，我们将开发一种用于光子的量子存储器，它可以高效率和非常低的噪声长时间存储短脉冲。为此，我们将使用“拉曼存储器”，这是我们团队首创的一种方法，它使用强大的激光脉冲使光子被通常透明的原子样本吸收。因为吸收是由强激光(不被吸收)产生的，所以激发的原子不会产生噪音，原子也不需要通过冷却或捕获它们来特殊准备。我们设计的简单将使我们能够建立第一个实际可行的存储器，它甚至可能能够在孤立的、恶劣的环境中工作，比如在海底。这也将允许我们进行新的光子学实验，这些实验太复杂了，如果没有存储器就无法操作。我们还将开发一种微型存储器，可以批量生产，并与现有的电信光纤集成。这样的设备对量子光子学的作用就像晶体管对传统电子的作用一样。量子存储器将开启量子设备的新纪元，拥有超快的计算机、完美的安全通信和超精确的测量。我们的研究是将这些真正神奇的技术带到生活中的关键。

Imagine a banknote that cannot be forged, because the serial number is scrambled every time someone tries to read it. But if you are the banker, you can read it. Sounds like Harry Potter? Imagine a computer that predicts how drugs will behave by simulating all possible chemical reactions at once! This is not an idea from Phillip Pullman's fantasy of parallel universes. Real technologies like this are just around the corner.This is the fascinating, counter-intuitive world of quantum physics. Huge advances in communications and computing technology over the last several decades have made this the information age and changed the way people live and interact even more drastically than did the industrial revolution. These advances have piggy-backed on the development of devices such as semiconductor transistors and lasers, devices which wouldn't be possible without the weird properties of quantum physics.But although modern computers have far-outstripped the early technology of punch cards and vacuum tube valves, at an underlying conceptual level, they still use exactly the same type of information - strings of 0s and 1s called bits. Quantum physics will allow us go far beyond this into the strange world of quantum information, where the "quantum bits" can be both 0 and 1 simultaneously! Computers that could work with this sort of information would be exponentially faster at performing difficult simulations or cracking codes. And communicating using quantum information can be made "eavesdropper proof" - perfectly secure.Over the past ten years, an enormous research effort has brought these extraordinary technologies from abstract ideas to small-scale experiments. One of the most promising ways to build a quantum computer is based on single particles of light, called photons, which can be sent over long distances in optical fibres and manipulated with ordinary lenses and mirrors. But like normal computers, quantum computers need memories to be able to synchronise different parts of a computation by storing the quantum information until it is needed. So to build a photonic quantum computer, we also need to have a quantum memory that can store single photons. What makes this difficult is that these special memories need to be able to store the fragile quantum information without destroying or even "looking" at it (measuring it).In this project, we will develop a quantum memory for photons which can store short pulses for long times with high efficiency and very low noise. To do this, we will use a "Raman memory", an approach pioneered in our group which uses a strong laser pulse to cause the photon to be absorbed by a sample of atoms which is normally transparent. Because the absorption is created by the strong laser (which is not absorbed), there is no noise from excited atoms, and the atoms don't need to be specially prepared by cooling them or trapping them.The simplicity of our design will allow us to build the first practically feasible memory, which would even potentially be capable of operating in isolated, harsh environments, such as on the ocean floor. This will also allow us to perform novel photonics experiments which are too complex to operate without the memory. We will also develop a miniaturized memory that could be mass-produced and integrated with existing telecoms fibres. Such a device will do for quantum photonics what the transistor did for conventional electronics.Quantum memories will open the way to a new era of quantum enabled devices, with super-fast computers, perfectly secure communications and ultra-precise measurements. Our research is the key to bringing these truly magical technologies to life.