Quantum Measurements with Photons

光子的量子测量

• 批准号: EP/F008023/1
• 负责人: Jeremy O'Brien
• 金额: $ 47.24万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FF008023%2F1
• 关键词: Quantum; Measurements; Photons

Measuring the length of an Olympic swimming pool doesn't affect how much water it has in it! We normally don't expect measuring things to change them. In the quantum world, things are very different.Quantum mechanics tells us how the world works at its most fundamental level. It predicts very strange behaviour that can typically only be observed when things are very cold and very small. It has an inbuilt element of chance, allows superpositions of two different states, and includes super-strong correlations between objects that would be nonsensical in our everyday world - entanglement . Despite this strange behaviour, quantum mechanics is the most successful theory that we have ever had - it predicts what will happen almost perfectly! However, it is not completely understood, and some of its implications are still being discovered.One of the great mysteries of quantum mechanics - The Measurement Problem - seeks to answer the question Why don't we see superpositions in the everyday world? ( alive and dead for example). Measurements play a special role in quantum mechanics and have been the subject of intense debate since the theory's development early last century. Recently quantum measurements have emerged to become an important practical issue. This is the result of the advent of quantum information science , which seeks to answer the question What advantage can be gained by specifically harnessing quantum mechanical effects in the storing, transmitting and processing of information? Anticipated future technologies include quantum computers with tremendous computational power, quantum metrology which promises the most precise measurements possible, and quantum cryptography which is already being used in commercial communication systems, and offers perfect security.Unlike measuring the length of a pool, measuring a quantum system necessarily disturbs the system. For example a standard measurement of a system in a superposition of two states finds the system in one of those states with some probability. After the measurement, the system is no longer in a superposition, but is in the state it was measured to be in with certainty. The original superposition state can never be recovered, and that information is lost.More general quantum measurements involve a payoff between the information gained and the disturbance of the system. Quantum mechanics also allows entangling measurements on two or more systems, that leave them in an entangle state. Finally, we can intentionally manipulate the system being measured depending on what the measurement tells us - feedback.These general quantum measurements could play an important role in future quantum technologies: the security of quantum cryptography relies on detecting an eavesdropper by the disturbance their measurements must cause; quantum metrology requires entangled measurements; and some schemes for quantum computation proceed via measurements alone.Single particles of light - photons - are excellent system for developing new quantum measurements, because they suffer from almost no noise. They also have great potential for application in future quantum technologies: schemes for all optical quantum computers are leading contenders, and photons are the obvious choice for both quantum communication and for quantum metrology schemes for measuring optical path lengths. This project will realise new quantum measurements which are entangled, tuneable in the amount of disturbance, and include feedback. It will use an optical crystal to produce up to six photons, optical circuits to realise controlled interactions between them (with feedback), and standard avalanche photodiodes to detect them. A particular focus will be on developing practical schemes for efficiently extracting information from quantum measurements. Finally, the project will design and implement techniques for distinguishing between quantum processes on up to 4 photons.

测量奥林匹克游泳池的长度并不会影响里面的水量！我们通常不期望测量能够改变它们。在量子世界中，情况非常不同。量子力学告诉我们世界在最基本的层面上是如何运作的。它预测了非常奇怪的行为，通常只有在物体非常冷且非常小的时候才能观察到。它具有内在的偶然性元素，允许两种不同状态的叠加，并包括物体之间超强的相关性，而这在我们的日常世界中是无意义的——纠缠。尽管有这种奇怪的行为，量子力学仍然是我们所拥有的最成功的理论——它几乎完美地预测了将会发生的事情！然而，它还没有被完全理解，并且它的一些含义仍在被发现。量子力学的最大谜团之一——测量问题——试图回答为什么我们在日常生活中看不到叠加的问题？ （例如生和死）。测量在量子力学中发挥着特殊作用，自上世纪初该理论发展以来一直是激烈争论的主题。最近，量子测量已成为一个重要的实际问题。这是量子信息科学出现的结果，它试图回答这样一个问题：通过专门利用量子力学效应在信息的存储、传输和处理中可以获得什么优势？预期的未来技术包括具有巨大计算能力的量子计算机、承诺最精确测量的量子计量学以及已经在商业通信系统中使用并提供完美安全性的量子密码学。与测量水池的长度不同，测量量子系统必然会干扰系统。例如，对处于两种状态叠加的系统的标准测量发现系统以一定概率处于这些状态之一。测量后，系统不再处于叠加状态，而是确定地处于测量时的状态。原始的叠加态永远无法恢复，并且该信息会丢失。更一般的量子测量涉及获得的信息和系统扰动之间的回报。量子力学还允许对两个或多个系统进行纠缠测量，使它们处于纠缠状态。最后，我们可以根据测量告诉我们的信息（反馈）有意地操纵被测量的系统。这些通用的量子测量可能在未来的量子技术中发挥重要作用：量子密码学的安全性依赖于通过测量所引起的干扰来检测窃听者；量子计量需要纠缠测量；一些量子计算方案仅通过测量进行。单个光粒子（光子）是开发新量子测量的优秀系统，因为它们几乎没有噪声。它们在未来量子技术中也具有巨大的应用潜力：所有光学量子计算机的方案都是领先的竞争者，而光子是量子通信和测量光路长度的量子计量方案的明显选择。该项目将实现新的量子测量，这些测量是纠缠的、扰动量可调的，并且包括反馈。它将使用光学晶体产生多达六个光子，使用光学电路来实现它们之间的受控相互作用（带反馈），并使用标准雪崩光电二极管来检测它们。特别关注的是开发实用方案，以有效地从量子测量中提取信息。最后，该项目将设计和实现区分最多 4 个光子的量子过程的技术。

项目成果

Integrated quantum photonics

• DOI: 10.1364/qim.2012.qm3b.1
• 发表时间: 2012-03
• 期刊: 2012 12th IEEE International Conference on Nanotechnology (IEEE-NANO)
• 作者: K. Aungskunsiri;D. Bonneau;J. Carolan;E. Engin;D. Fry;J. Hadden;P. Kalasuwan;J. Kennard;S. Knauer;T. Lawson;L. Marseglia;E. Martin-Lopez;J. Meinecke;G. Mendoza;A. Peruzzo;K. Poulios;N. Russell;A. Santamato;P. Shadbolt;J. Silverstone;A. C. Stanley-Clark;M. Halder;J. Harrison;D. Ho;P. Jiang;A. Laing;M. Lobino;J. Matthews;B. Patton;A. Politi;M. R. Verde;Pei Zhang;X. Zhou;M. Cryan;J. Rarity;M. G. Thompson;Siyuan Yu;J. O'Brien

Fibre implementation of a controlled-NOT gate

受控非门的光纤实现

• DOI: 10.1109/qels.2008.4553037
• 发表时间: 2008
• 期刊: Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series
• 作者: Fulconis J.

Fibre Source of Intrinsically Time Bandwidth Limited Photon Pairs

本质时间带宽有限光子对的光纤源

• DOI: 10.1364/iqec.2009.itue3
• 发表时间: 2009
• 作者: Fulconis J

Quantum information processing with optical fibres

光纤量子信息处理

• 发表时间: 2008
• 期刊: Optics InfoBase Conference Papers
• 作者: Fulconis J

Publisher's Note: Entanglement-enhanced quantum key distribution [Phys. Rev. A 78 , 032314 (2008)]

出版商注释：纠缠增强量子密钥分配 [Phys.

• DOI: 10.1103/physreva.78.039904
• 发表时间: 2008
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: Ahonen O