Quantum properties of polariton condensates in microcavity devices

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

Abstract

Semiconductor microcavities (MC) are Fabry-Perot resonators which consist of high reflectivity mirrors and which contain embedded quantum wells in the active region. They enable both exciton and photon confinement in one direction. Strong exciton-photon coupling in these structures results in the formation of a new class of bosonic quasiparticles, described in terms of two-dimensional polaritons or mixed exciton photon states. Microcavity polaritons have favourable characteristics for the study of condensation phenomena and novel many body effects such as superfluidity in a solid-state system, which can be achieved at much higher temperature than that required for excitons and atoms due to their very small effective mass. An additional advantage of MC structures is that precise manipulation of the polariton states can be performed on a micrometer scale by an external laser field. In addition, strong polariton-polariton interactions enable the generation of non-classical states of photons. Also the internal structure of polariton states can be easily modified by the appropriate design of MC structures with resultant zero- or one- dimensional confinement. The key aim of my proposal will be accurately prepared macroscopically occupied high density polariton states with precise phase information and control of their polarisation and statistical properties. In order to prove the analogy with atomic condensates, but in a solid state system, one of the important parts of my proposal is dedicated to the study of spatial and temporal coherence of two interacting polariton condensates. Specially designed zero-dimensional photonic structures will also permit control of quantum fluctuations, which affect the coherence. Efficient generation of non-classical states of photons, squeezed light with polarisation selective control will be achieved using resonant excitation of the polariton ground states. Polaritonic states will be controlled by external applied uniaxial strain and applied magnetic field to achieve desired spin properties of polaritons and hence the polarisation of the polariton condensate. The proposed research will also focus on the study of interactions between the high density polariton phase and acoustic phonons, which will be important to understand new phenomena arising from condensation in the periodic potential induced by surface acoustic waves. Finally, the effects of squeezing and coherence properties of the polariton condensate will be investigated in wide band microcavities. The research is expected to lay a strong foundation for the future use of microcavity structures in quantum information technology and for the development of novel light sources, mixers and tunable optical filters.

Publications

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Amo A (2009) Collective fluid dynamics of a polariton condensate in a semiconductor microcavity. in Nature

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Cerda-Méndez EA (2010) Polariton condensation in dynamic acoustic lattices. in Physical review letters

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Khalifa A (2008) Electroluminescence emission from polariton states in GaAs-based semiconductor microcavities in Applied Physics Letters

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Krizhanovskii D (2009) Coexisting nonequilibrium condensates with long-range spatial coherence in semiconductor microcavities in Physical Review B

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Krizhanovskii D (2008) Self-organization of multiple polariton-polariton scattering in semiconductor microcavities in Physical Review B

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Krizhanovskii DN (2010) Effect of interactions on vortices in a nonequilibrium polariton condensate. in Physical review letters

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Love AP (2008) Intrinsic decoherence mechanisms in the microcavity polariton condensate. in Physical review letters

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Sarkar D (2010) Polarization bistability and resultant spin rings in semiconductor microcavities. in Physical review letters

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Sich M (2011) Observation of bright polariton solitons in a semiconductor microcavity in Nature Photonics

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Walker P (2011) Suppression of Zeeman splitting of the energy levels of exciton-polariton condensates in semiconductor microcavities in an external magnetic field. in Physical review letters

 
Description In GaAs-based semiconductor microcavities strong coupling between photonic mode and exciton state (bound electron-hole pair) in quantum wells results in formation of hybrid light-matter particles described as microcavity polaritons. The important property of the polariton system is a strong optical nonlinearity arising from strong exchange polariton-polariton interactions due to admixture of the excitonic component. Such interactions, which are orders of magnitude stronger than those in weakly coupled systems, can be used potentially for development of novel optoelectronic devices performing all-optical processing. Furthermore, the small effective mass of polaritons arising from the steep photonic dispersion (and hence small density of polariton states) enables nonequilibrium Bose-Einstein condensation to be achieved at relatively high temperatures (up to 50 K) and weak optical resonant or nonresonant excitation. Polariton condensates emit coherent light, which in combination with strong nonlinearity makes the polariton microcavity system attractive for building of new coherent light sources, frequency converters, switches and modulators. The main beneficiaries from the research outcome of my grant are among academic communities, working on the development of novel optoelectronic devices, classical and quantum integrated active optical components for computational and telecommunication purposes. There are several major outcomes, which have a potential to be used in future applications. Firstly, we have observed bright polariton solitons in semiconductor microcavities. Solitons are nondiffracting nondispersive localised wavepackets, which are stabilised by strong optical nonlinearities. Polariton solitons are hybrid light-matter solitons, which are reported for the first time here. They have well-defined shape, small size (2-5 micrometers) and amplitude determined by the internal microcavity properties and pump conditions. Importantly, they propagate with a high speed of ~1.5microns/ps and can be switched on and off on a ps timescale. Because of such unique properties polariton solitons can be used potentially as optical bits in all optical digital processing schemes operating at Tbit/s rate. Real applications of these hybrid light-matter solitons can be realised in strongly coupled semiconductor microcavities based on GaN material, where microcavity polaritons may exists at 300 K and above. Recently, nonequilibrium BEC of polaritons has been reported in GaN-based microresonators. Secondly, we were able to demonstrate the efficient creation of the coherent polariton states carrying Orbital Angular Momentum (OAM). OAM is represented by a phase vortex in polariton field, where the phase of a condensate winds around a point in space linearly with azimuthal angle. OAM can take integer positive or negative number and hence may represent a number of bits of information: vortices may thus have advantages over spins of photons for efficient use in quantum information technology. In our work we imprinted a phase vortex state on a polariton condensate using a steering optical beam carrying OAM. We also observed that pair polariton-polariton scattering from a pump state with no vortex to polariton condensate carrying the imprinted vortex results in a creation of an antivortex state in the idler condensate. Such vortices were shown to be metastable on a timescale of several hundreds picoseconds, which is much longer than polariton lifetime. Thirdly, we investigated polariton condensates subject to periodical potential created by surface acoustic wave, which modulates both the energies of the exciton states and photonic mode. We were able to observe transition from spatially extended coherent polariton condensate into an array of localised polariton 1D condensates with increase of the amplitude of surface acoustic wave. In future we expect to realise quantum regime of such transition, where each of the localised polariton states contains only a few of even a single polariton. Such an array of strongly localised states will represent an array of identical single photon sources. This has a strong potential to be applied in quantum optical circuits performing quantum processing. Finally, we investigated the first and the second order temporal coherence of polariton condensates in CdTe based microcavities. We observed that at high polariton densities polariton-polariton interactions tend to introduce some decoherence into the system. Nevertheless, such decoherence can be overcome at higher optical powers well above condensation threshold, when fluctuations of particle density occur on quite fast timescale. This research proves that polariton condensates can be used as coherent low threshold light sources despite strong interactions in the system.
Exploitation Route Our research revealed several interesting phenomena, which can be further used for development of arrays of identical single photon sources and novel light sources emitting coherent straight or twisted light (with vortices). Polariton solitons form a foundation for building compact, energy efficient digital circuits performing all-optical signal processing on a fast picoseconds timescale. The potential beneficiaries are commercial companies working in optoelectronic industry and information and communication technology. We have been disseminating our results via publications in high profile high impact journals such as Phys.Rev.Letters, Nature family magazines etc read by broad scientific community. Several presentations at national/international conferences (ICPS, OECS, CLEO/QELS, MSS, EP2DS, PLMCN etc) and presentations and seminars in academic and industrial institutions were given. 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. We highlight our research outcomes on the website of our group http://ldsd.group.shef.ac.uk/ucavity/.
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 from the research outcome of the grant are among academic communities, working on the development of novel optoelectronic devices, classical and quantum integrated active optical components for computational and telecommunication purposes. There are three major outcomes, which have a potential to be used in future applications. Firstly, we have observed bright polariton solitons in semiconductor microcavities. These solitons have well-defined shape and amplitude determined by the internal microcavity properties. They can be switched on and off on a ps timesclale and hence potentially can be used as optical bits for all optical digital processing schemes operating at Tbit/s rate. Real applications of these hybrid light-matter solitons can be realised in strongly coupled semiconductor microcavities based on GaN material, where microcavity polaritons may exists at 300 K and above. Secondly, we were able to demonstrate efficient creation of coherent polariton states carrying Orbital Angular Momentum (OAM). OAM can be any integer and may represent a number of bits of information: vortices may thus have advantages over spins of photon for efficient use in quantum information technology. Finally, we were able to observe transition from spatially extended coherent polariton condensate into an array of localised polariton condensates by controllable application of the surface acoustic wave. In future we expect to realise quantum regime of such transition, where each of the localised polariton states contains only a single polariton emitting a single photon. Such an array of single photon emitters can be potentially used in development of quantum optical circuits to build powerful quantum optical computers. 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 Semiconductor Integrated Quantum Optical Circuits
Amount £5,040,713 (GBP)
Funding ID EP/J007544/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2012 
End 01/2017
 
Title New optical method 
Description We developed new type of streak camera imaging technique, which allows to record movies with a typical resolution time of 1 picosecond. This appears to be essential to observe new state of matter, such as polariton condensation, superfluidity and solitons. We also develpoed a technique for creation of OAM of light, which can be imprinted onto polariton condensate 
Type Of Material Technology assay or reagent 
Year Produced 2009 
Provided To Others? Yes  
Impact As a result of providing a technique to imprint vortices onto polariton condensates to Madrid group under supervision of Prof. Luis Vina, it became possible to observe metastable condensate flows 
 
Description Polariton condensation in Surface Acoustic Lattices 
Organisation Paul Drude Institute for Solid State Electronics
Country Germany 
Sector Academic/University 
PI Contribution This work has been done in collaboration with the group of Prof. Paulo Santos from PDI, Berlin, Germany. Dr. Santos's group has a strong experience in fabrication high quality SAW devices. Optical measurements on polariton condensation is such devices were performed both in Sheffield and Berlin. Fundamental effects such as spatial and temporal coherence of modulated polariton system were adressed. This research looks very promising for applications such as optical modulators and switches due to the advantage of controlling polariton-phonon coupling within sub-nanosecond time scale.
Start Year 2008
 
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