Joel Cox receives prestigious “Sapere Aude” grant

As a theoretical physicist Joel Cox has specialized in the fields of nanophotonics, nonlinear and quantum optics, and condensed matter physics during his research at The Institute of Photonic Sciences (ICFO) in Barcelona, the Max Planck Institute for Quantum Optics in Munich, and now the Centre for Nano Optics at the University of Southern Denmark. Cox is regarded as one of the leading theoretical researchers in the field of nonlinear graphene nano-optics.

Nanophotonics or nano-optics is the study of the behaviour of light on the nanometer scale. As Cox explains it, his research is basically about finding new ways to control light on the nanoscale:

Light is an electromagnetic wave, and the size of the wave is hundreds of nanometers, which limits how small we can focus it with conventional optics. If we would like to use light in miniaturized devices, say, the way we now use electrons in integrated computer chips, we need to find different ways to manipulate it on much smaller length scales.
- Joel Cox

Using graphene to trap light

Joel Cox’s research focuses on how light interacts with two-dimensional, atomically-thin materials, in particular the new material graphene.

Back in 2004 the Russian physicists Andre Geim and Konstantin Novoselov isolated and characterized graphene – an achievement that they received the Nobel Prize in Physics for only six years later.

Graphene is a two-dimensional material consisting of a single layer of carbon atoms arranged in a honeycomb lattice. It is a relatively strong material, and its electrons move in special ways that make it a very good conductor of electricity. Due to its unique electronic properties, and because it is atomically thin, it is also very useful in nanophotonics, where physicists can use special light-matter excitations in graphene called “plasmon polaritons” to trap light and compress it.


A new paradigm for computing?

It’s incredible how fast modern technology has developed. Just try to recall how your mobile phone looked like 10 years ago. Now, try to imagine what it will look like in 10 years.

Right now, electronic components like those in our mobile phones contain transistors that work with binary 0-1 switches. These switches are being fabricated on sizes of tens of nanometers, so that we can fit millions of them on a single chip, but it is challenging to go any further because they generate enormous heat, and we even might have to worry about quantum mechanical effects. Therefore, scientists are looking for fundamentally new ways to build fast and stable devices that use less energy — photonic devices, that operate with light instead of electricity, might be one solution.

I’m really honoured to have been awarded this prestigious grant—this is a huge boost to my research efforts, and I am looking forward to building a strong research team dedicated to the project I am passionate about.
- Joel Cox

In the new research project “Towards single-photon nonlinear optics in atomically-thin materials”, Joel Cox will seek to engineer the extreme light confinement associated with two-dimensional polaritons in atomically-thin materials like graphene to actuate nonlinear optical phenomena at ultra-low powers. Nonlinear optical effects are needed to control light with light itself and could allow us to build the photonic analogues of our existing electronic devices. The problem is that light doesn’t easily interact with itself, so nonlinear optical processes are inherently weak and thus inefficient.

The discovery of graphene and other atomically-thin materials might turn out to be a new paradigm for nonlinear optics. As Cox explains it, polaritons, formed when light hybridizes with polarizable excitations in matter, can focus optical fields on the nanoscale to boost light-matter interactions, and this way reduce the light intensity threshold required to trigger nonlinear optical effects.

In atomically-thin materials, these polaritons are extremely-confined, so this effect becomes stronger than ever. In other words, if we can use polaritons in atomically-thin materials to compress light so strongly that it starts interacting with itself, we can create a non-linear interaction where light signals control what other light signals do. Then, with “ultrafast” pulses of light that are extremely short in time, we might be able to replace our electronic switches with optical ones, and this way build faster devices that don’t require as much energy.

If the light concentration becomes strong enough, there is a possibility to achieve nonlinear optical interactions with individual photons, the quantum particles of light; this represents the ultimate limit of nonlinear optics, and, besides maximizing the performance of existing classical nonlinear optical technologies, single-photon optical nonlinearity holds tremendous prospects for nanoscience and quantum information technology.


Being a DIAS Fellow

At the Centre for Nano Optics Joel Cox collaborates with DIAS Chair, Professor N. Asger Mortensen and DIAS Chair, Professor Sergey I. Bozhevolnyi. It was Mortensen who initially introduced Cox to the idea of becoming a DIAS Fellow. One of the things that attracted Cox is the emphasis on curiosity-driven research at DIAS.

Cox has now been a DIAS Fellow for two years. As he says, the first year was amazing with inspiring lectures and an international environment with fellows from around the world. To him, it felt very much like an academic startup. This year we lost some momentum due to the COVID-19 restrictions, but Cox is convinced that DIAS still has a lot of potentials that we haven’t tapped into yet.  

For more information about Joel Cox, please refer to the SDU Research Portal.