Queen's University

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Stephen Hughes

Small but Mighty

[Stephen Hughes]
Photo by Bernard Clark

“Sorry,” I ask incredulously, “What do you mean, you can stop light?”

Professor Stephen Hughes (Physics, Engineering Physics and Astronomy) looks at me with a smile and continues: “Well, slow it down to a near standstill. I know, it's crazy. Our team has even made a t-shirt that says: ‘We're faster than the speed of slow light.’ And it isn’t a pipe dream. This is a fabricated structure.”

Hughes is attempting to explain to me some of the seemingly impossible things done in nanophotonics and the strange behaviour of photons at the nano-scale. His research is on the cutting edge of new information technologies that work by manipulating light particles (photons) in ways analogous to how integrated circuits manipulate electrons. And just as integrated circuits and electronic computers had world-changing effects in the last century, Hughes, and many others, believe that photonics (and nanophotonics in particular) is poised to bring about a similar technological revolution in this century.

There are many advantages to communicating and computing with photons rather than electrons. For one thing, unlike electrons, photons can be sent over very long distances with virtually no loss of signal. A photonic integrated circuit could also do more while producing less heat and using up less energy. And the behaviour of photons, particularly at the quantum level, will allow for types of computation and control that are not practical or not possible with traditional electronic computers.

Yet, the challenges are very real. At the scale of everyday life, individual photons are particularly difficult to control. Not only do individual photons interact with the physical materials around us, but they also “see” an electromagnetic vacuum through which they travel – a vacuum swarming with virtual particles of all sorts. And that is why physicists like Hughes are delving into the realm of the nano-scale – a domain that is 100 times smaller than the thickness of a human hair, where a tiny material can be fabricated to help control and manipulate light-matter interactions. For example, the science and techniques of Cavity Quantum Electrodynamics (or Cavity QED) involve the use of very small materials (photonic cavities) in which photons can be tamed to behave in a quantum mechanical way where quantum coherence overcomes the unavoidable effects of dissipation.

That’s what’s coming. It is a new emerging field of quantum optical physics that largely has not been explored.

At the classical level of a few photons (for example, from an attenuated laser), where the photons are distinguishable, usually one can operate in a realm of “so many, every so often,” but by carefully manipulating the photonic environment in which a quantum emitter finds itself, you can start to emit precise numbers of indistinguishable single photons within discrete times, alter their direction, slow them down, and even entangle them over large distances (“spooky action at a distance”). And just as in silicon semiconductor technology, these tiny photonic widgets can be grown and replicated to produce combinations of behaviours to accomplish new and exciting things, including quantum cryptography. Some of this technology is already in use: in specialized detectors, solar collectors and telecommunication devices, and secure communications. Yet there is still much work to be done to turn it into a mainstream technology.

[Stephen Hughes and his team]
Dr. Stephen Hughes with Dr. Nishan Mann and MSc student Chelsea Carlson.

“On one hand,” Hughes explains, “as you go down to this scale, there are a lot of interesting things that will happen even at the classical level. But the quantum stuff has largely been untouched for these types of structures. And I think the regime of ‘quantum nanophotonics’ is perhaps the next big thing.”

While much of his work is developing the theoretical framework and models for new nanophotonic technologies, a significant portion of his efforts are spent in collaborating with researchers and experimental groups around the world, and helping them to interpret their experimental results and design next-generation devices. The science of nanophotonics is still so young that analyzing the real-world behaviours of optical and nano-mechanic materials is a work in progress, often requiring new theoretical tools and models to make sense of the new data. Much of what needs to be worked out is at the quantum level, which presents many big challenges and exciting prospects for new science.

Hughes leans forward to describe the big picture: “That’s what’s coming. It is a new emerging field of quantum optical physics that largely has not been explored.”

Towards this vision, Hughes has begun to put together a multidisciplinary research team of computational scientists, physicists, theorists, experimentalists, chemists, and engineering physicists to develop the theory, modelling tools, and the technologies needed to underpin this emerging field of quantum optical technologies.

I leave our discussion with a heightened sense of what this technological future has in store.

Lowell Cochrane
(e)AFFECT Issue 11 Spring/Summer 2017

Learn more about: Dr. Hughes' research