Observation of Quantum Interference in the Plasmonic Hong-Ou-Mandel Effect

G. Di Martino, Y. Sonnefraud, M. S. Tame, S. Kéna-Cohen, F. Dieleman, Ş. K. Özdemir, M. S. Kim, and S. A. Maier

Phys. Rev. Applied 1, 034004 – Published 15 April 2014

Abstract

Surface plasmon polaritons (SPPs) are electromagnetic excitations coupled to electron-charge density waves at metal-dielectric interfaces. They have recently been found to enable a range of nanophotonic devices for controlling systems at the quantum level, including single-photon sources, transistors, and ultracompact quantum circuitry. An important quantum feature of SPPs yet to be fully explored is their bosonic nature. In this work, we report direct evidence of the bosonic nature of SPPs in a scattering-based beam splitter. A parametric down-conversion source is used to produce two indistinguishable photons, each of which is converted into a SPP on a metal-stripe waveguide and then made to interact through a semitransparent Bragg mirror. In this plasmonic analog of the Hong-Ou-Mandel experiment, we measure a coincidence dip with a visibility of 72%, a key signature that SPPs are bosons and that quantum interference is clearly involved. Our work opens up possibilities for the study of fundamental quantum effects in plasmonic systems and their related applications.

Received 30 January 2014

DOI:https://doi.org/10.1103/PhysRevApplied.1.034004

Authors & Affiliations

G. Di Martino¹, Y. Sonnefraud^1,2, M. S. Tame^1,3,*, S. Kéna-Cohen^1,4, F. Dieleman¹, Ş. K. Özdemir⁵, M. S. Kim⁶, and S. A. Maier^1,†

¹Experimental Solid State Group, Imperial College London, Blackett Laboratory, SW7 2AZ London, United Kingdom
²Institut Néel, CNRS UPR2940, 25 rue des Martyrs, 38042 Grenoble, France
³University of KwaZulu-Natal, School of Chemistry and Physics, 4001 Durban, South Africa
⁴Department of Engineering Physics, École Polytechnique de Montréal, C.P. 6079 succursale Centre-ville, Montréal, Québec H3C 3A7, Canada
⁵Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130, USA
⁶Quantum Optics and Laser Science Group, Imperial College London, Blackett Laboratory, SW7 2AZ London, United Kingdom

^*markstame@gmail.com
^†s.maier@imperial.ac.uk

High-Visibility On-Chip Quantum Interference of Single Surface Plasmons

Yong-Jing Cai, Ming Li, Xi-Feng Ren, Chang-Ling Zou, Xiao Xiong, Hua-Lin Lei, Bi-Heng Liu, Guo-Ping Guo, and Guang-Can Guo

Phys. Rev. Applied 2, 014004 (2014)

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Issue

Vol. 1, Iss. 3 — April 2014

Subject Areas

Plasmonics

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Images

Figure 1
Experimental setup. (a) Photon pair generation. Photon pairs are generated via spontaneous parametric down-conversion by using a pump laser focused onto a BBO crystal and filtered by using interference filters (IFs). Each photon is coupled into a single-mode fiber (SMF). (b) Microscopy. The photons from the SMFs are collimated and half-wave plates (HWPs) are used to optimize SPP excitation. A time delay is introduced on one path. (c) Plasmonic beam splitter. The photons are focused onto separate spots on the input gratings by using a microscope objective. The beams at the output gratings are collected and coupled into multimode fibers (MMFs). (d) Detection and analysis. The outputs of the MMFs are sent to avalanche photodiodes $B_{1}$ and $B_{2}$ , where coincident detection events are measured.
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Figure 2
Plasmonic beam splitter. (a) Optical image of the beam splitter. The in and out gratings consist of 11 ridges, each being repeated at an increment of $g = 620 nm$ from the waveguide end. The distance between gratings is $L = 12.5 μ m$ . The Bragg reflector is made out of three ridges with a center-to-center distance of $p = 500 nm$ . (b) Intensity outcoupled from a single waveguide as a function of length when excited by a laser at 808 nm by using the method in Ref. [26]. (c) Optical image of the splitter when the SPPs are excited by a laser at 808 nm focused on the top-left grating. Light is outcoupled at the top right and bottom right with almost identical intensity. The integration time is adjusted to give a reasonable contrast for the output, leading to a saturation at the input caused by the scattered field. (d) Transmission $T$ and reflection $R$ as a function of wavelength.
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Figure 3
Plasmonic Hong-Ou-Mandel dip. Black squares: Coincidence rate as a function of time delay $Δ t$ . The red curve is a theoretical fit, $N (Δ t)$ , based on the coincidence probability $P (Δ t)$ corrected for accidentals [38]. From the theory fit, we extract a coherence time for the SPPs of approximately 0.1 ps, which is consistent with the coherence time obtained from the measured photonic dip. This result confirms that during the photon-SPP conversion process the coherence properties of the single-photon wave packets and the single SPPs are similar and that the wave packet has not been significantly altered by the conversion process or propagation. The inset shows the singles rates (in counts/h) as a function of $Δ t$ : red disks for detector $B_{1}$ and black circles for $B_{2}$ . The visibility obtained from the plasmonic dip is $V_{SPP} = 0.72 \pm 0.13$ .
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