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Article:Stevenson, R.M., Astratov, V.N., Skolnick, M.S. et al. (6 more authors) (2000) Continuous wave observation of massive polariton redistribution by stimulated scattering in semiconductor microcavities. Physical Review Letters, 85 (17 ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. A massive redistribution of the polariton occupancy to two specific wave vectors, zero and ϳ3.9 3 10 4 cm 21 , is observed under conditions of continuous wave excitation of a semiconductor microcavity. The "condensation" of the polaritons to the two specific states arises from stimulated scattering at final state occupancies of order unity. The stimulation phenomena, arising due to the bosonic character of the polariton quasiparticles, occur for conditions of resonant excitation of the lower polariton branch. High energy nonresonant excitation, as in most previous work, instead leads to conventional lasing in the vertical cavity structure.

Semiconductor microcavities can support quasiparticles which are half-light and half-matter with interactions possessed by neither component alone. We show that their distorted dispersion relation forms the basis of a quasiparticle ''trap'' and elicits extreme enhancements of their nonlinear optical properties. When driven by a continuous wave laser at a critical angle, the quasiparticles are sucked into the trap, condensing into a macroscopic quantum state which efficiently emits light. This device is thus an optical parametric oscillator based on quasiparticle engineering. In contrast to a laser, macroscopic coherence is established in the electronic excitations as well as the light field. This paves the way to new techniques analogous to those established in atomic and superconducting condensates, such as ultrasensitive solid-state interferometers.Parametric oscillators are nonlinear resonators in which a coherent pump wave is converted into coherent ''signal'' and ''idler'' waves of different frequency, thus forming the basis for broadband tunable sources and mixers.1 They have found widespread application in both microwave and optical frequency regions, as well as providing a ''quantum testbed'' for some of the most profound demonstrations of nonclassical photon states.2 The major stumbling block for optical parametric oscillators ͑OPO's͒ has been their inefficient optical nonlinearities, only recently improved with the introduction of periodically patterned media which modify the photon modes. In a similar fashion, the ability to control the wave functions of electrons by tightly confining them inside semiconductor heterostructures has revolutionized the science and technology of light emitters, modulators, and lasers. By combining these approaches a new generation of lightmatter interactions can be built which yield novel science and useful applications. This is most apparent in the vertical cavity surface emitting laser ͑VCSEL͒ which uses monolithic integration of a semiconductor quantum well ͑QW͒ emitter surrounded by highly reflecting semiconductor Bragg mirror stacks.3 By manipulating both the optical and electronic degrees of freedom, low-threshold highly efficient lasing is possible. This planar microcavity design has also shown bistability and amplification.4 However, such devices operate in a regime with a large density of excited electronhole pairs whose effect is to broaden the transitions and reduce their coupling to light. In the opposite limit, when highquality microcavities contain sufficient oscillator strength they can enter a new regime due to the strong coupling of light and matter, producing mixed ''exciton-polariton'' modes split in energy. 5,6 Much controversy in recent years has centered on whether strongly excited polaritons can show a new type of laser action known as a ''boser. '' 7-10 This confusion exists because the mixed exciton-photon states appear to possess properties inaccessible to their component particles.Here we report an optical parametric oscillation of a microc...

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