Polariton lasing and Bose-Einstein condensation in an electrically pumped system

Lead Research Organisation: University of Sheffield
Department Name: Physics and Astronomy


We propose to demonstrate the first electrically injected polariton laser. The physics underlying the operation of the laser, and the factors which lead to its optimum performance will be determined. The polariton laser is a new device concept which holds the promise of very low threshold coherent light emission, at the same time as corresponding to non-equilibrium Bose-Einstein condensation (BEC) in a solid state system. The strong coupling between excitons and photons in semiconductor microcavities leads to the formation of novel quasi-particles, exciton-polaritons. Such polaritons exhibit characteristic bosonic properties such as macroscopic occupation of individual quantum states and BEC in a system with long temporal and spatial coherence. Due to the photonic component of the polaritons, the macroscopically occupied polariton state emits coherent light, and forms the basis of a new type of light source, the polariton laser, in which coherent light is emitted without the need for population inversion. Until very recently nearly all work in this field has been carried out under conditions of optical excitation. From the device perspective, new impetus has been given by our recent observation of light emission from polariton states under electrical injection, followed very soon after by two other groups. This proposal aims to capitalise on our recent achievements and overall expertise in the field, to realise an important world first, the first electrically injected polariton laser, as required for real world applications of these novel devices.

Planned Impact

Our proposal has major potential for short, medium and long term impact. In the timescale of the programme the outcomes are likely to be of particular significance to researchers in the field, as summarised in the section on Academic Beneficiaries. The effectiveness of the dissemination to these beneficiaries will benefit strongly from our highly effective publication record in major journals, frequent invited and contributed talks at conferences, and past, present and future membership of several European collaborations in the polariton field. Further details are given in the Academic Beneficiaries section. In the longer term, the research is likely to be of very considerable significance in two applications directions. Firstly once its feasibility in GaAs-based structures is established in our programme, the basic ideas will be ready to be transferred to the more challenging GaN-materials system which has the material properties required for operation at room temperature. Such devices will operate in the blue and ultraviolet spectral regions. Main application areas are likely to be as low threshold light sources for data storage and printing applications where potential markets are huge in the $B range for e.g. next generation blu-ray etc. Based on past technological records, it is likely to take 5-15 years from first demonstration to real world exploitation. It is important that the feasibility of polariton laser action that we aim to demonstrate will play a critical role in providing the basis for transfer of the technology to wide band gap materials. Much of the basic technology for GaN vertical cavity emitters was put in place during the Framework 6 EU programme Stimscat which we coordinated. This programme included several of the major European laboratories engaged in GaN materials technology, including notably Sharp Laboratories of Europe. This programme established close links with workers at Sharp; these interactions will continue throughout the duration of the present project, as indicated in the letter from Sharp. We will keep Sharp well informed of progress we make, by holding annual meetings with them to update them on progress, and forwarding copies of publications to them. The associated industrial partners of the FP7 Training Network Clermont4, who include Sharp and also HORIBA, Hitachi Cambridge Laboratory, Finmecchanica, LUXTALTEK will provide further dissemination routes to industry through the annual meetings of all partners. The achievement of the world's first polariton laser has potential to generate significant publicity, and hence to be brought to the attention of a wide spectrum of industries. Following publication, the results will be advertised through trade magazines in the field, and the university of Sheffield press office, as well as dissemination routes through publication in high quality journals. The second area of application is in the area quantum information technology where the electrically injected polariton condensates have potential to be exploited as micron-scale alternatives to atomic condensates for quantum computation schemes. These topics are likely to be of main interest to academic groups for the foreseeable future. More details are thus given in the Academic Beneficiaries section.


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Description In GaAs-based semiconductor microcavities strong coupling between the photonic mode and the exciton states in quantum wells results in formation of hybrid light-matter particles described in terms of microcavity polaritons. The important property of the polariton system is a strong optical nonlinearity arising from exchange particle-particle interactions. Such a strong interaction can be used for development of novel optoelectronic devices performing all-optical processing at high speed given by short polariton dynamics. Furthermore, the small effective mass of polaritons allows Bose-Einstein condensation (BEC) at relatively high temperature and weak optical pumping to be achieved. Significant advances in understanding of polariton spin dynamics and in development of high quality microcavity structures, which are necessary for the realisation of electrically pumped polariton BEC, were made here. Firstly, polariton condensates (macroscopically occupied states) in magnetic field were investigated. A finite Zeeman energy splitting of the spin-polarised condensed states was observed at high magnetic field, a test for strong exciton-photon coupling in stimulated polariton emission. Interesting phenomena on interaction and coherent phase synchronisation between spin-polarised condensates were reported. A key property of equilibrium exciton-polariton condensates in semiconductor microcavities is the suppression of the Zeeman splitting under weak magnetic field. By studying magneto-photoluminescence spectra of polariton condensate emission from a GaAs microcavity, we show experimentally that a similar effect occurs in a non-equilibrium polariton condensate arising from polariton parametric scattering. In this case, the quenching of Zeeman splitting is related to a phase synchronization of spin-up and spin-down polarized polariton condensates caused by a nonlinear coupling via the coherent pump state. Secondly, we employed high quality microcavity samples to study spatial nonlinear optical effects (solitons) in these structures. Solitons are stable non-diffracting non-spreading localised wavepackets supported by intrinsic nonlinearity of the media they exist in. Solitons can be observed in many areas of physics- pure optical solitons in fibers, semiconductor lasers and gas vapours were reported as well as solitons in cold atom gases were observed. The polariton solitons are shown to be micron-scale localised non-diffracting wavepackets with a corresponding broad spectrum in momentum space. Unlike solitons known in Bose condensed atomic gases, they are non-equilibrium and rely on a balance between losses and external pumping. Microcavity polariton solitons are excited on picosecond timescales, and thus have further benefits for the information processing over the light only solitons in semiconductor cavity lasers, which have nanosecond response time. In particular, it is possible to explore polariton solitons in construction of high frequency (THz) all optical logic miniature gates. Finally, we grew high quality microcavity structure with doped bottom and top DBRs. Microcavity pillars defining the size of the laser were fabricated using optical lithography and chemical etching. These devices show polariton laser-like emission. Strong coupling has been confirmed by observing Zeeman splitting of stimulated emission at high magnetic field. The final steps in the fabrication of the electrically pumped polariton laser (fabrication of electrical contacts and electroluminescence) will be carried out in the near future. In addition, the high quality etched microcavity structures, such as pillars and micro-wires will be used to investigate quantum effect such as polariton blockade leading to single photon emission and development of an array of undistinguishable single photon sources. Such emitters are important for optical quantum computational schemes and quantum telecommunications.
Exploitation Route The outcomes of our research provide the proof of concept, which can be further used for development of novel light sources with low threshold currents, novel single photon sources as well as all-optical digital devices performing signal processing on a fast picoseconds timescale. The potential beneficiaries are commercial companies working in optoelectronic industry and information and communication technology. The way to put our research outcomes in use is to ensure an efficient dissemination of our results through publications in high impact journals (Phys.Rev.Letters, Nature family journals etc) , presentations at national/international conferences (ICPS, OECS, CLEO/QELS) and presentations and seminars in academic and industrial institutions. Our membership of the EU ITN Clermont4 with 14 partners, spread around 6 countries in Europe also provided ways of further effective dissemination and contacts with several industrial companies via research meetings.
Sectors Digital/Communication/Information Technologies (including Software),Education,Electronics

URL https://ldsd.group.shef.ac.uk/group-members/dr-dmitry-krizhanovskii/
Description The main beneficiaries of the research are among academic communities working on the development of novel coherent light sources. Although the main aim of the current proposal- realisation of low threshold electrically pumped polariton laser has not been achieved yet, significant advances in understanding of polariton spin dynamics and in development of high quality microcavity structures were made, which are important for future development of miniature ultra-low-power threshold devices employed in all-optical signal processing. Polariton laser arises from Bose-Einstein condensation of hybrid light-matter particles- polaritons. Its main advantage over semiconducotor lasers is a strong reduction of threshold. Room temperature polariton states can be achieved in GaN microcavities in UV range. In a longer term low threshold GaN microcavity polariton laser as well as polariton logic gates and switches can be realised, which will have a high impact on optoelectronic industry developing coherent blue and UV light source as well as all-optical circuits. The final steps in fabricating of electrically pumped polariton laser will be attempted. In addition, the high quality microcavity structures, such as pillars and microwires will be used to investigate quantum effect such as polariton blockade leading to single photon emission and development of an array of undistinguishable single photon sources. Such emitters are important for optical quantum computational schemes and quantum telecommunications. In the longer term companies such as IBM, Oclaro, Nanoplus, Sharp etc potentially will benefit from the research conducted within this grant programme. Close interaction with some of these firms has been already established.
Sector Digital/Communication/Information Technologies (including Software),Education,Electronics
Impact Types Cultural

Description Conferences 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The results were presented at several international conferences such as PLMCN, ICPS, MSS, CLEO, ICSCE, EP2DS, ICPS etc.

A number of invited presentations were given at the following conferences

List of invited talks:

International School for Young Scientists "Laser Physics and Photonics"
7.11.2014 - 17.11.2014, Suzdal/Vladimir, Russia. "Lecture on nonlinear polaritons"

UK-Russia scientific workshop in Saint Petersburg on polaritonics 24-26 March 2014
"Polariton solitons in microcavities and waveguides with giant optical nonlineairy"

Advanced Workshop on Non-Equilibrium Bosons: from Driven Condensates to Non-Linear Optics 19 - 23 August 2013 "Nonlinear polaritonics in semiconductor microcavities and waveguides in the strong coupling regime"

International Workshop on Polaritonics in Tarbert, Scotland, UK 16-20 February, 2013 "Collective properties of polaritons in semiconductor microcavities"

11th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, Stuttgart, Germany, 23-27 Sept 2012 "Bright polariton solitons in semiconductor microcavities"

Photon 12, Durham , UK, 3-6 Sept 2012 "Bright polariton solitons, soliton trains and soliton spin properties in strongly coupled semiconductor microcavities"

POLATOM Network Conference:Cold Atoms, Excitons, Polaritons, Bose-Einstein condensates 9-14 Sept 2012, Cambridge , UK "Bright polariton solitons in semiconductor microcavities"

International Conference On Spontaneous Coherence in Excitonic Systems 6, Stanford, USA, 27-31 August 2012 "Bright polariton solitons, soliton trains and soliton spin properties in strongly coupled semiconductor microcavities"

the Vth International School on Nanophotonics and Photovoltaics (ISNP-2012). Phuket, Thailand, 30th March - 6th April 2012. " Lecture on Polariton solitons"

the 1st International Workshop "Relativistic Phenomena in Solids, Le-Mont-Dore, France 11-15 March 2012 "Nonlinear localised polariton wavepackets"

International Workshop: Nonlinear Photonics, St Petersburg, Russia, August 24-26, 2011."Direct observation of bright polariton solitons in semiconductor microcavities"

The 40th International School and Conference on the Physics of Semiconductors "Jaszowiec" 2011, June 25th - July 1st, Krynica-Zdroj, Poland "Polariton condensation in dynamic acoustic lattices"

NANO 2011 symposium, Yekaterinburg, Lenevka, Russia, June 20-24, 2011 "Bright polariton solitons and polarisation bistability in semiconductor microcavities"

Winter Colloquium on the Physics of Quantum Electronics PQE-2011, Snowbird, Utah, USA Jan 2-6, 2011. "Effect of interactions on collective polariton states"

Physics of Light-Matter Coupling in Nanostructures, Cuernavaca, Mexico, April 2010
"Spatial coherence and vortices of polariton condensates"

UK-Japan Workshop-Novel Phenomena and Techniques in Semiconductor Nanostructures, Tokyo, Japan 22 Jan 2010 "Coherence and vortices in polariton condensates"

Nonlinear Photonics in Micro- and Nanostructures, IOP London, 10 Dec 2009
"Spatial coherence and vortices of polariton condensates"

NANO2009 symposium, Minsk, Belarus, June 22-26, 2009 "Nonequilibrium and equilibrium features of polariton condensates"

Physics of Light-Matter Coupling in Nanostructures, Leece, Italy, April 2009 "Polariton condensates in disorder and periodical transverse potential"

International Conference On Spontaneous Coherence in Excitonic Systems 4, Cambridge , 8-12 Sept 2008. "Intrinsic decoherence mechanisms and formation of coexisting polariton condensates in CdTe microcavities "
Year(s) Of Engagement Activity 2008,2009,2010,2011,2012,2013,2014