Hybrid Polaritonics

Hybrid polaritonics combines the properties of different light emitting materials - organic polymers and semiconductors - in order to produce quasiparticles that combine the possibilities of both systems. "Polaritons" are quasi-particles that arise from strong coupling between light and matter. This means that they have hybrid properties, combining the mobility and flexibility of light, with the possibilities of interactions due to the matter component. At high enough densities, or low enough temperatures, polaritons can form a macroscopic coherent quantum state, a polariton condensate, or a polariton laser. Such a coherent state shows much of the same physics as Bose Einstein Condensation, as has been seen for cold atoms, but without requiring the ultra-low tempeatures required for atoms.

Hybid polaritonics focuses on how, by combining different "matter" parts of the polariton, one can push these temperatures even higher, up to room temperature, and how one can engineer completely tunable system. The matter part of a polariton can come from any material which will absorb and emit light at a specific wavelength. Much existing work on polaritons is based on the material being inorganic semiconductors. These can be grown controllably, and one can drive such devices by passing an electrical current through them to make a polariton laser. However, the coupling between matter and light in semiconductors is not strong enough for these devices to work at room temperature. In contrast, organic molecules and polymers can show huge coupling strengths, but are generally poor electrical conductors. Our programme is to combine the benefits of both systems to provide a whole set of devices, operating at room temperature, based on the formation of polaritons. These devices will range from polariton lasers (providing a route to easily tunable lasers with very low threshold currents), to Terrahertz light sources (with applications in non-invasive medical imaging and explosives detection), to ultra-efficient light emitting diodes.
To reach these ambitious objectives, we need to combine expertise from a wide number of fields. Our team contains world experts in light emitting polymers, semiconductor growth, characterisation and spectroscopy of polaritons, and in theoretical modelling. Members of our team have previously achieved the first realisations of polariton lasing, of strong coupling with organic materials, and of building hybrid polariton lasers. The possibility to combine this expertise draws on the unique strengths that the UK currently has in this area, and enables the combination of this expertise to be focussed on providing room temperature devices based on hybrid polaritonics, and to revolutionise this field.

The economic impact of investment in fundamental science based around photonic /
optoelectronic technologies is significant. The European Commission Photonics 21
industry group has stated "Photonics technologies underpin at least 10% of the
European economy, and that reliance will increase as those technologies are further
developed in the next decade." The growing importance of photonics is also recognized
by the EU Photonics Unit, who predict that photonic technologies will have a growth
rate > 8% and will reach a global market of Eur 600 Bn by 2020. Indeed, there are
around 500 companies in Europe that currently develop photonic technologies and
employ 300,000 people (mostly in SMEs). Major growth is expected in the coming years,
however it is clear that developments over time scales of 15+ years will only come
through continued state-sponsored basic research in projects such as that proposed
here.
Our Programme Grant is designed to address the development of new physics that will
feed into advanced optoelectronic devices. Polaritonic technologies - devices based on
polariton physics - are set to bring the exotic world of quantum coherent phenomena
into everyday life. The physics that we will develop will directly underpin the
development of technologies that rely on the quantum-mechanical properties of excitonpolaritons.
Such technologies are anticipated to have significant social and commercial
value, as they will directly address a number of areas including medicine, environmental
protection, security, data-communication, and computing.
The polariton devices that will be designed and studied will include polariton logic gates
and optical integrated circuits, polariton sources of non-classical light and entangled
photon pairs and polariton-based quantum annealing processors. The realisation of
these devices would be a giant step forward in development of quantum technologies, in
particular, quantum simulators. This project thus directly addresses one of the Grand
Challenges in Physical Sciences formulated by the EPSRC: Quantum Physics for New
Quantum Technologies. The direct beneficiaries of our work include the banking sector,
security and communication industries.
Further applications of our research are anticipated in low-cost, portable and coherent
terahertz radiation sources. Such technologies are anticipated to have a range of
applications from the non-invasive detection of cancers in the human body to the
detection of the chemical signatures of explosives. We will also explore speculative ideas
to use polariton physics to improve the emission efficiency of organic light-emitting
diodes. Here, our goal is to bypass the (normally non-emissive) triplet states formed in
an OLED device and rapidly transfer them to emissive polariton states. If successful, this
concept could present a significant opportunity to OLED display manufacturers, as this
would allow triplet states to be harvested without the necessity to use expensive
platinum or iridium metal complexes in display technology. Progress in this area could
produce valuable intellectual property that could be exploited in the highly lucrative
OLED display market that is expected to reach $25.9bn by 2018 (Transparency Market
Research).
This project will also have direct impact through the training given to a number of
PDRAs and postgraduate students (from relevant CDTs or DTGs) who will be closely
involved with the research. This training - in both experimental and theoretical
methods - will help provide a cohort of highly skilled researchers who are prepared for
careers in both academic and industrially based research in the areas of photonics and
optoelectronics.