Quantum Optics Seminar by Reinier Heeres – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Reinier Heeres

Surface plasmon polaritons (plasmons) are a hybrid combination of light and a collective oscillation of the free electron plasma at a metal-dielectric interface [1]. This interaction allows to confine light to the nanoscale, below the diffraction limit that is present for dielectric structures. We use this fact to realize a plasmonic beam splitter based on sub-wavelength gold waveguides in a directional coupler geometry. Integrated superconducting single-photon detectors [2, 3] allow to study this beam splitter on the quantum level using photon pairs created by spontaneous parametric down-conversion. We show that plasmons excited by these photon pairs remain coherent by observing Hong-Ou-Mandel interference [4]. This hallmark quantum effect causes indistinguishable particles simultaneously arriving at a beam splitter to exit through the same port, i.e. bunch. With this experiment we prove the quantum nature of surface plasmons and pave the way for optical quantum logic gates at the nanoscale and for efficient photon extraction from single-photon sources. 

[1] Barnes, Dereux & Ebbesen, Nature 424 (2003) [2] Gol'tsman et al.,  APL 79 (2001) [3] Heeres et al., Nano Letters 10 (2010) [4] Hong, Ou & Mandel, PRL 59 (1987)