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

点击翻译按钮获取中文摘要

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.