One-dimensional quantum emitters and photons for quantum technologies: 1D QED

量子技术利用了光子和电子等粒子的内在量子性质。人们已经知道，控制这些粒子的确切状态并精确控制它们如何相互作用的能力，将在各种技术应用方面带来前所未有的突破。量子技术的直接目标之一是利用这样一个事实，即量子粒子在保留其所有信息的同时永远不能被复制。由于粒子不能被克隆，人们可以用这种方式对密钥进行编码，因为窃听者可以通过在测量过程中改变光子状态来揭示它们的存在。然而，由于需要确保每个比特只传输一个光子，因此实用的密码学“量子密钥分配”具有有限的信息传输速率。为了确保只产生一个光子，需要一个来自量子发射器(如原子)的“单光子源”，或者在我们的例子中，需要一个“人造原子”，即一个量子点。我们将制造单光子源，将光子以非常高的效率输出到有用的电信波长(1300 Nm)的光纤中。量子技术的长期目标是创造一台“通用量子计算机”。这将使用量子粒子作为“量子比特”，显示出“叠加”(一次使一个粒子处于两种状态的能力)和“纠缠”(共享几个粒子之间的叠加)的性质。操纵量子比特的相互作用导致了一种执行计算的方法，其复杂性随着量子比特的数量呈指数级增长。然而，为一台可以执行任何计算的量子计算机(一台“通用”计算机)准备状态是非常具有挑战性的。然而，如果一个人有一个特别复杂的问题要解决，他可能会转向量子模拟。在这种情况下，可以预先编程计算。众所周知，通过使用光子电路(本质上是由反射镜和分束器的等价物组成的光子电路)，人们可以执行量子模拟。建立了多个通道的网络，并将单个光子输入到选定的通道中。然而，一个重要的要求是，同样，受控的单光子必须是可用的。这些要求比量子通信更严格。第二个要求是每个光子在带宽、波长和偏振方面必须完全相同--这就是众所周知的“不可区分”。输入到分束器上的不可分辨的光子会经历起逻辑门作用的量子干涉。难以分辨的单个光子极难产生。然而，在利用光学腔中的单原子精确控制单光子方面，已经取得了很大的进展。然而，原子发射光子的速度很慢，收集所有光子是困难的。目前，单光子的产生速率仍然太低，实验装置非常大，除了实验室外，不适合在任何地方使用。然而，量子点具有与原子非常相似的性质。它们发出的光比原子快得多(以每秒10亿个光子的速度)，也可能被合并到半导体“腔”中。在这项提议中，我将展示人们可以使用与电信网络中使用的光纤技术类似的光纤技术来非常高效地收集光。通过这样做，我将为量子通信网络和量子模拟设备提供单光子源。这将导致绝对安全的通信，以及计算新材料或复杂分子的性质以帮助设计新药物的能力，并将密码学中使用的大素数因式分解。

Quantum technologies exploit the intrinsic quantum nature of particles such as photons and electrons. It has been known for some time that the ability to control the exact state of these particles, and to precisely control how they interact, will lead to unprecedented breakthroughs in a variety of technological applications. One of the immediate goals of quantum technologies is to exploit the fact that quantum particles can never be copied whilst retaining all of their information. Because the particle cannot be cloned, one may encode a cryptographic key in this way, as an eavesdropper would reveal their presence by changing the photon state as it is measured. Practical cryptographic "quantum key distribution", however, has limited information transfer rate by the fact that one needs to ensure that only one photon is transmitted per bit. To make sure that exactly one photon is generated, a "single photon source" from a quantum emitter such as an atom is required, or in our case, an "artificial atom", a quantum dot. We will fabricate single photon sources that output photons with very high efficiency into a fibre at a useful telecommunications wavelength (1300nm).The long-term goal of quantum technologies is to create a "universal quantum computer". This would use quantum particles as "quantum bits" that show the property of "superposition" (the ability to prepare a particle two states at once) and "entanglement" (sharing the superposition between several particles). Manipulating quantum bit interactions leads to a way of performing calculations with a complexity that speeds up exponentially with number of quantum bits. Preparing states for a quantum computer that will perform any calculation (a "universal" computer), however, is very challenging.Nevertheless, if one has a particular complex problem to solve, one may turn to quantum simulation instead. In this case, a calculation may be pre-programmed. It is known that by using photonic circuits (essentially a photon circuit consisting of the equivalent of mirrors and beamsplitters) one may perform a quantum simulation. A network of many channels is set up, and single photons input into chosen channels. However, an important requirement is that, again, controlled single photons must be available. The requirements are more stringent than for quantum communication. A second requirement is that each photon must be absolutely identical in bandwidth, wavelength and polarization - this is known as "indistinguishability". Indistinguishable photons input onto a beamsplitter undergo quantum interference that acts as a logic gate.Truly indistinguishable single photons are extremely difficult to create. Nevertheless, a great deal of progress has been made in precisely controlling single photons using single atoms trapped in an optical cavity. However, atoms emit photons slowly, and collecting all photons is difficult. The rate at which single photons can be generated is presently still too low and the experimental setup involved very large, and unsuitable for anywhere except a laboratory.However, quantum dots have very similar properties to atoms. These emit light far faster than atoms (at a rate of 1 billion photons per second) and may also be incorporated into semiconductor "cavities". In this proposal, I will show that one may collect the light extremely efficiently using similar optical fibre technology to that used in telecommunication networks. By doing this, I will provide single photon sources to quantum communication networks and quantum simulation devices. This will lead to absolutely secure communications, and the ability to calculate properties of novel materials or complex molecules to help design new drugs, and factorize large prime numbers used in cryptography.