potential

DR ELENA OSTROVSKAYA Dr Elena Ostrovskaya discusses her role in establishing Australia’s first research programme in theoretical and experimental polaritonics and the exciting new developments currently underway in the field

Can you discuss some of the most significant local support for both theory and important technological benefits to have experiment. The ANU also hosts a node of resulted from the field’s development, the Australian National Fabrication Facility, elaborating on the key objectives of your which enables customised post-processing of current project? experimental samples.

The development of polaritonics has so far How does your collaboration with Dr focused on proof-of-principle demonstrations Robert Dall help lead this work? of devices that explore the unique properties of polaritonics that stem from their hybrid Dr Robert Dall is a highly skilled and very light-matter nature. These devices explore experienced experimentalist in the field of ultrafast polariton velocities that are close ultracold atomic physics and a driving force to those of , high nonlinearities behind the experimental development of inherited from , and spin degrees the project. We work as a team, with Dall of freedom. running the experiments, me providing theory support and guidance, and both of us equally My project focuses on both fundamental contributing to the strategic planning of the and applied aspects of the -polariton research programme. What initially drew you to the field BEC inside semiconductor microcavities. of polaritonics? The theoretical and experimental goals Robert Dall’s previous experience is in are twofold: first and foremost, we plan building the most sophisticated apparatus My PhD research was in the field of theoretical to create tailored polariton BEC systems for Bose condensing metastable Helium and nonlinear optics and , and I that will enable us to probe into several experiments on Helium BECs. He became have extensive expertise in this area. After fundamental problems of modern physics, interested in polaritonics around two or three completing my PhD, I was drawn to the topic namely emergent properties of non- years ago and is enthusiastic about the new of Bose–Einstein condensation of ultracold equilibrium systems, dissipative superfluidity possibilities offered by this physical system. atoms due to the interesting and, at the time, and quantum turbulence. Second, we seek little explored parallels between the nonlinear to identify and characterise novel properties You are aiming to create the first state-of- physics of coherent light and matter . of polariton BECs that can be potentially the-art experimental facility in Australia Bose–Einstein condensates (BECs) offer a harnessed in semiconductor microcavity dedicated to research in polaritonics. How possibility to create, probe and manipulate a devices for emission and control of coherent far along are you in realising this vision? quantum mechanical state on a macroscopic light, and bring new functionality to the next scale, and I found this window into the generation of optoelectronic devices for use Within the past year, with help from our quantum world fascinating. in optical integrated circuits, classical and collaborators (Dr M Fraser, Professor S quantum logic elements, optical switches and HÖfling and Dr C Schneider), this vision has In recent years I became aware of the progress spin-memory elements. become a reality. The experimental facility in polaritonics, which transfers the physics is currently up and running and we are now of Bose–Einstein condensation from the What makes the Australian National able to focus on physics rather than on highly demanding environment of ultracold University (ANU) particularly well placed building an apparatus. There will be essential temperatures and ultrahigh vacuum to a much for research on polaritonics? modifications and improvements that will less formidable setting of well-developed take place with every new experiment, but semiconductor technology and cryogenic The ANU is an ideal place to host the the core of the facility is in place. Our next or even room temperatures. Apart from the polaritonics project because of the combined goal is to expand the polaritonics research possibility to explore the fundamental physics cross-disciplinary expertise of the people in Australia, involving more people across of condensates in a much more accessible involved. In particular, our team has a lot institutions. In particular, we have initiated physical system, polaritonics offers a new of experience in nonlinear and singular discussions with Professor Matthew Davis of platform for novel optoelectronic devices for optics and physics of quantum degenerate Queensland University in the hope to expand emitting and controlling light, and my interest gases. The other important factors are the the research programme on non-equilibrium lies in its potential technological applications. already existing infrastructure and the properties of polariton condensates.

10 INTERNATIONAL INNOVATION DR ELENA OSTROVSKAYA Harnessing half-light half-matter

A collaborative team at the Australian National University has developed the country’s fi rst experimental facility dedicated to polaritonics, putting Australia on the map of this rapidly expanding fi eld

IT IS DIFFICULT to overestimate the fundamental aspects of the polariton BEC. In understanding role optoelectronics plays in an increasing range how to control, structure and manipulate their of modern technologies. As two-way optical- collective state in a semiconductor microcavity, electrical transducers, optoelectronic devices Ostrovskaya and Dall hope to continue unlocking can source, detect and control light within the the highly promising potential of polaritonics in all the way from driving forward next-generation optoelectronics. visible infrared and ultraviolet light to invisible gamma rays. Over time these properties have From the confl uence of semiconductor physics, enabled the development of diverse technologies optoelectronics, photonics and the fi eld of such as light-emitting diodes (LEDs), solar cells BECs, the physical systems brought to life in and semiconductor lasers. Firmly entrenched polaritonics are born. It is natural, therefore, that in the cutting-edge and the everyday, one has Ostrovskaya’s work is a wide collaborative effort only to look as far as any wireless or fi bre optic tapping into many different areas of expertise, communication network to fi nd optoelectronic even more so given the very close interaction devices keeping the world ticking along. between the theoretical and experimental sides. Contributors from Germany, Japan, Singapore Recently, developments within the emerging fi eld and the UK are involved in designing and running of polaritonics have heralded the beginning of joint experiments at the ANU, the fabrication of a new era of optoelectronic devices. Stemming microcavities, and theoretical collaborations. from the physics of ultracold bosonic atoms, the arrival of polariton Bose–Einstein condensates THE BEST OF BOTH WORLDS (BECs) has the potential to help create extremely sophisticated devices that outstrip their forebears The operation of polariton-based devices is in a variety of ways. A relatively new fi eld, reliant on the quantum mechanical effects of polaritonics is moving with such rapidity that it is light-matter interactions in semiconductor not yet fully represented across the international microcavities. Comprising millions of particles science community. Within just a few years, all forced into the same quantum state, BECs are however, Australia’s shortage of polaritonics one of the most controllable quantum systems expertise has improved dramatically with a we have access to and, due to their relatively dedicated exciton-polariton experimental facility large size for a quantum system, among the combined with a theory programme bringing the easiest to examine. In order to form a BEC from country to the fore. neutral atoms one needs access to an advanced apparatus able to achieve temperatures within a millionth of a degree of absolute zero. Polariton PROMISING POTENTIAL BECs, however, are not made from atoms. An Australian Research Council (ARC) Future Fellow at the Australian National University’s With semiconductor microcavities, collective (ANU) Nonlinear Physics Centre (NLPC), Dr Elena quantum effects can be produced at the interface Ostrovskaya is working closely with her colleague between light and matter. A trapped Dr Robert Dall, a Research Fellow at the NLPC and in such a microcavity bounces to and fro and ANU’s Atomic & Molecular Physics Laboratories, interacts with excitons to produce a new hybrid to study both the fundamental and applied particle that is part light and part matter. This

Left: schematics of a chiral polaritonic lens showing the distribution of light intensity in a structured optical pump. Right: experimental image of a polariton vortex created by the lens.

WWW.RESEARCHMEDIA.EU 11 INTELLIGENCE NONLINEAR POLARITONICS: HARNESSING COLLECTIVE BEHAVIOUR OF HALF-LIGHT HALF-MATTER OBJECTIVES • To create tailored polariton Bose–Einstein condensate (BEC) systems to study the emergent properties of non-equilibrium systems, dissipative superfl uidity, and quantum turbulence • To identify and characterise novel properties of polariton BECs that can be potentially harnessed in semiconductor microcavity devices for emission and control of coherent Left: a structured optical pump creating a double well potential for . Right: polariton condensate light, and bring new functionality to the next trapped in the potential. generation of optoelectronic devices for use in optical integrated circuits, classical and is the exciton-polariton. The unique properties demonstrate novel ways of manipulating and quantum logic elements, optical switches and derived from its hybrid nature mean polariton controlling polariton condensates. spin-memory elements based systems are often a more attractive option KEY COLLABORATORS than their light or matter counterparts for a variety As an example, the experiments at ANU have of applications. Take the conventional photon demonstrated a new concept in the control Dr Robert Dall; Dr Anton Desyatnikovl; Professor Yuri Kivshar, Research School of laser: large amounts of energy are consumed in of light and matter using polaritonic lenses – Physics and Engineering, Australian National a requisite process called population inversion. structured laser beams that focus and direct the University, Australia • Dr Michael Fraser, This employs optical pumping, the raising fl ow of polaritons. In particular, it was shown that Quantum Optics Research Group, RIKEN of electron energy levels to reach an excited using a chiral polaritonic lens – a structured laser Center for Emergent Matter Science, Japan • majority. A polariton laser, on the other hand, is beam with a chiral density distribution (an object Professor Sven Höfl ing, School of Physics and able to emit coherent and monochromatic light is said to be chiral when it cannot be superimposed Astronomy, St Andrews University, UK • Dr without population inversion so that its operation with its mirror image by a simple rotation) – it is Christian Schneider, Technische Physik and consumes a remarkably small amount of energy possible to produce polariton condensates hosting Wilhelm-Conrad-Röntgen Research Center in comparison. a vortex: “Using a spatial distribution of pump for Complex Material Systems, Universität Würzburg, Germany • Dr Timothy Liew; spots with broken chiral symmetry, we were able Professor Ivan Shelykh, Division of Physics Unlike its ultracold atom predecessors, a polariton to controllably create polariton condensates with and Applied Physics, Nanyang Technological BEC can be obtained at both cryogenic and a twisted phase – polariton vortices,” elaborates University, Singapore • Dr Oleg Egorov, room temperatures in a solid state. Polaritonics, Ostrovskaya. Creation of polariton vortices is an Institute of Condensed Matter Theory and therefore, has a dual benefi t; while making the important ingredient in fundamental studies of Solid State Optics, Abbe Center of Photonics, technologically promising physics of condensates polariton condensates and applications. Vortices Friedrich-Schiller-Universität Jena, Germany far more accessible, polaritonic devices could be are extremely robust states protected by their FUNDING easily incorporated into standard optoelectronic topology, and every ‘twist’ of the phase around a circuits due to their inherent semiconductor vortex core can be used, for instance, to encode Australian Research Council (ARC) Future interface. Potential technological applications of information. In microcavities, the phase of Fellowship FT110100064 (2012-15) polaritonic devices include low power coherent polaritons can not always be precisely enforced ARC Discovery Project DP130100855 (2013-15) light sources, sensors, memory storage and a and therefore, up to now, controlled excitation variety of information processing elements. of polariton vortices has been a diffi cult problem. CONTACT The collaborative experiments conducted at the Dr Elena Ostrovskaya ANU facility therefore have set the foundation for POLARITON PARADIGMS ARC Future Fellow future studies in the fi eld. Nonlinear Physics Centre Now with an experimental facility dedicated to exciton-polariton physics at ANU’s Research Research School of Physics and Engineering FACILITATING PROGRESS The Australian National University School of Physics and Engineering, Ostrovskaya Canberra, 0200 is hopeful that the team’s work will succeed in There are still many avenues yet to be explored Australia demonstrating effi cient ways of shaping and regarding the fundamental and applied aspects guiding the polariton fl ow, a fundamental aspect of exciton-polariton BECs inside semiconductor T +61 2 61253798 E [email protected] to be considered in the design of polaritonic microcavities. The project’s groundbreaking work devices. More specifi cally, Ostrovskaya and Dall on the control of polariton currents via the use of http://bit.ly/1BmxRoE hope to learn more about the strong nonlinear polaritonic lenses and structured potentials is set http://polaritonbec.wordpress.com interaction between polaritons, the inherent to continue. Among the closest goals is realising spin structure of exciton-polariton systems and topologically protected transport of exciton- ELENA OSTROVSKAYA graduated with an the essentially non-equilibrium nature of the polaritons and exploring fundamental non- MSc degree in Theoretical Physics from Moscow polariton BEC. Hermitian quantum mechanics with polariton State University, Russia, in 1994. In 1999, she systems. Back in 2006 when the Bose–Einstein obtained a PhD from the Research School At the University of Würzburg’s Technische Physik, condensation of polaritons was fi rst observed, the of Physics and Engineering, The Australian Dr Christian Schneider has been fabricating project currently underway at ANU would have National University, where she is currently a structured growth microcavities, created using been a highly speculative proposal, but today it is tenured academic. a novel etch and overgrowth technique, for the made possible by the considerable rate of progress project at the ANU: “With these samples, we can in the fi eld of polaritonics. Where there was explore behaviour of polariton condensates in once a lacuna of expertise in exciton-polariton periodic potential (photonic lattices) of complex physics in Australia, the ANU’s fi rst dedicated geometries,” explains Ostrovskaya. So far, using experimental facility is now contributing both structured optical pumps and structured generously to the international development of growth microcavities, they have been able to next generation optoelectronics.

12 INTERNATIONAL INNOVATION