Physicists develop record-breaking source for single photons

物理学家为单光子开发了创纪录的光源

by University of Basel

巴塞尔大学

The new single-photon source is based on excitation of a quantum dot (shown as a bulge on the bottom left), which then emits photons. A micro-cavity ensures that the photons are guided into an optical fiber and emerge at its end. Credit: University of Basel, Department of Physics

新的单光子源基于量子点的激发（在左下角显示为凸起），然后发射光子。微腔确保将光子导入光纤并在其末端出射。图片来源：巴塞尔大学物理系

Researchers at the University of Basel and Ruhr University Bochum have developed a source of single photons that can produce billions of these quantum particles per second. With its record- breaking efficiency, the photon source represents a new and powerful building-block for quantum technologies.

巴塞尔大学和波鸿鲁尔大学的研究人员已经开发出一种单光子源，每秒可以产生数十亿个这样的量子粒子。光子源凭借其破纪录的效率，代表了量子技术的一个强大的新组成部分。

Quantum cryptography promises absolutely secure communications. A key component here are strings of single photons. Information can be stored in the quantum states of these light particles and transmitted over long distances. In the future, remote quantum processors will communicate with each other via single photons. And perhaps the processor itself will use photons as quantum bits for computing.

量子密码术保证绝对安全的通信。这里的关键组件是单光子串。信息可以存储在这些光粒子的量子状态中，并可以长距离传输。将来，远程量子处理器将通过单个光子相互通信。也许处理器本身将使用光子作为计算的量子位。

A basic prerequisite for such applications, however, is an efficient source of single photons. A research team led by Professor Richard Warburton, Natasha Tomm and Dr. Alisa Javadi from the University of Basel, together with colleagues from Bochum, now reports in the journal Nature Nanotechnology on the development of a single-photon source that significantly surpasses previously known systems in terms of efficiency.

但是，此类应用的基本先决条件是有效的单光子源。由巴塞尔大学的Richard Warburton教授，Natasha Tomm和Alisa Javadi博士以及Bochum的同事领导的研究小组现在在《自然纳米技术》杂志上报道了单光子源的发展，该光子源的发展大大超越了先前已知的系统在效率方面。

"Funnel" guides light particles

“漏斗”引导轻粒子

Each photon is created by exciting a single "artificial atom" (a quantum dot) inside a semiconductor. Usually, these photons leave the quantum dot in all possible directions and thus a large fraction is lost. In the photon source now presented, the researchers have solved this problem by positioning the quantum dot inside a "funnel" to send all photons in a specific direction.

通过激发半导体内部的单个“人工原子”（量子点）来创建每个光子。通常，这些光子在所有可能的方向上离开量子点，因此损失了很大一部分。在现在提出的光子源中，研究人员通过将量子点放置在“漏斗”中以将所有光子按特定方向发送来解决了这个问题。

The funnel is a novel micro-cavity that represents the real innovation of the research team: The micro-cavity captures almost all of the photons and then directs them into an optical fiber. The photons, each about two centimeters long, emerge at the end of an optical fiber.

漏斗是一种新颖的微腔，代表了研究团队的真正创新：微腔捕获几乎所有的光子，然后将它们引导到光纤中。每个大约两厘米长的光子出现在光纤的末端。

The efficiency of the entire system—that is, the probability that excitation of the quantum dot actually results in a usable photon—is 57 percent, more than double that of previous single- photon sources. "This is a really special moment," explains lead author Richard Warburton. "We've known for a year or two what's possible in principle. Now we've succeeded in putting our ideas into practice."

整个系统的效率（即量子点的激发实际上产生可用光子的概率）为57％，是以前的单光子源的两倍以上。主要作者理查德·沃伯顿（Richard Warburton）解释说：“这是一个非常特殊的时刻。 “我们已经知道原则上可能的一两年了。现在我们已经成功地将我们的想法付诸实践。”

Enormous increase in computing power

极大地提高了计算能力

The increase in efficiency has significant consequences, Warburton adds: "increasing the efficiency of single photon creation by a factor of two adds up to an overall improvement of a factor of one million for a string of, say, 20 photons. In the future, we'd like to make our single- photon source even better: We'd like to simplify it and pursue some of its myriad applications in quantum cryptography, quantum computing and other technologies."

Warburton补充说，效率的提高将产生重大后果：“将单个光子的创建效率提高两倍，一串20个光子的总效率将提高一百万。在未来，我们希望使我们的单光子源更好：我们希望简化它，并在量子密码学，量子计算和其他技术中追求其无数的应用。”

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来源于：Phys