In this experiment, pairs of identical photons at 806 nm through a single-photon down conversion in a nonlinear crystal that are sent onto a plasmonic platform were generated. The plasmonic platform consists in several elements that are etched on a 300 nm-thick gold film on top of a silica substrate, on a total 40x40μm footprint. The input channels of the plasmonic platform are made of two unidirectional launchers. Those asymmetric 11-grooves gratings have been designed to efficiently couple a normally incident Gaussian mode into directional SPPs. The SPPs generated by each launcher then freely propagate and recombine on the surface plasmon beamsplitter (SPBS). It is made of two identical grooves in the metallic surface, oriented at 45° with respect to the propagation direction of waves. The succession of metal and air allows a scattering process that generates both a transmitted and a reflected SPP. The SPPs then propagate towards two large outcoupling strip slits. They are decoupled into photons propagating in the glass substrate on the rear of the platform.
In this experiment, pairs of identical photons at 806 nm through a single-photon down conversion in a nonlinear crystal that are sent onto a plasmonic platform were generated. The plasmonic platform consists in several elements that are etched on a 300 nm-thick gold film on top of a silica substrate, on a total 40x40μm footprint. The input channels of the plasmonic platform are made of two unidirectional launchers. Those asymmetric 11-grooves gratings have been designed to efficiently couple a normally incident Gaussian mode into directional SPPs. The SPPs generated by each launcher then freely propagate and recombine on the surface plasmon beamsplitter (SPBS). It is made of two identical grooves in the metallic surface, oriented at 45° with respect to the propagation direction of waves. The succession of metal and air allows a scattering process that generates both a transmitted and a reflected SPP. The SPPs then propagate towards two large outcoupling strip slits. They are decoupled into photons propagating in the glass substrate on the rear of the platform.
Surface plasmon polaritons (SPPs) result from collective oscillations of free electrons coupled to an electromagnetic field at a plane interface between a metal and a dielectric medium. As photons, SPPs can be considered either as waves or as bosonic particles [1] and they can experience striking quantum interferences such as Hong-Ou-Mandel (HOM) effect [2]. We use in this paper a plasmonic platform (Fig.1) that can convert photons into plasmons, and separate or recombine them on a plasmonic beamsplitter [3]. Single SPPs are excited using single photons created by parametric down conversion into a periodically-poled KTP crystal. The platform is placed in a Mach-Zehnder interferometer in order to vary the path difference between SPPs before impinging on the beamsplitter. The setup allows us to revisit quantum optics experiments using SPP as carriers of the quantum of energy. Using the same device, we can test the wave-particle duality, two-particle (HOM) interference and non-local control of single plasmon interference using the entanglement between a photon and a SPP [4]. In the case of the HOM experiment, we demonstrate that the losses can be used as a new degree of freedom [5]. Playing with the dephasing between transmission and reflection coefficient of the beamsplitter, we can observe a peak instead of the usually expected dip in the HOM interference (Fig.2), i.e. an anti-coalescence effect of SPP. In this talk, we will introduce the plasmonic device main features as well as the different quantum plasmonics experiments that have been performed thanks to the SPP beamsplitter. These results are essential to understand the SPP quantum behavior or to develop hybrid plasmon-photon systems for potential future applications in quantum communication mediated by SPP. [1] JM Elson and R.H. Ritchie, Phys. Rev. B 4, 4129 (1971) [2] J.S. Fakonas et al., Nat. Phot. 8, 317 (2014) [3] M.C. Dheur et al. , Sc. Advances 2, e151574 (2016) [4] M.C. Dheur et al. ArXiv 1610.07493, B. Vest et al. ArXiv 1610.07479 [5] S. Barnett et al., Phys. Rev. A 57, 2134 (1998) Fig.1: Plasmonic platform used for the quantum optics experiment (B). It consists in two SPP launchers (A), a plasmonic beamsplitter, and two slits to convert SPP to photons in the glass substrate. The plasmonic interference can thus be probed using single photon counting modules. Fig2: HOM experiment on a lossy plasmonic beamsplitter, whose complex amplitude reflection and transmission factors are denoted r and t respectively. The usual HOM dip is observed when r = it (left), a peak in the coincidence rate is shown when r = t.
In this presentation, we report direct evidence of the bosonic nature of SPPs in a scattering-based beamsplitter, in one of the most simple experiments of quantum optics - done using SPPs instead of photons propagating in air. 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 semi-transparent Bragg mirror. In this plasmonic analog of the Hong-Ou-Mandel experiment, we measure a coincidence dip with a visibility of 72%, the signature that SPPs are bosons and that quantum interference is clearly involved.
Previous experiments have shown that surface plasmon polaritons (SPPs) preserve their entangled state and do not cause measurable decoherence. However, essentially all of them were done using SPPs whose dispersion was in the linear “photon-like” regime. We report in this presentation on experiments showing how transition to “true-plasmon” non-linear dispersion regime, which occurs near SPP resonance frequency, will affect quantum coherent properties of light. To generate a polarization-entangled state we utilize type-I parametric down-conversion, occurring in a pair of non-linear crystals (BiBO), glued together and rotated by 90 degrees with respect to each other. For state projection measurements, we use a pair of polarizers and single-photon avalanche diode coincidence count detectors. We interpose a plasmonic hole array in the path of down-converted light before the polarizer. Without the hole array, we measure visibility V=99-100% and Bell’s number S=2.81±0.03. To study geometrical effects we fabricated plasmonic hole arrays (gold on optically polished glass) with elliptical holes (axes are 190nm and 240nm) using focused ion beam. When we put this sample in our system we measured the reduction of visibility V=86±5% using entangled light. However, measurement using classical light gave exactly the same visibility; hence, this reduction is caused only by the difference in transmission coefficients of different polarizations. As samples with non-linear dispersion we fabricated two-layer (a-Si - Au) and three-layer (a-Si – Au – a-Si) structures on optically polished glass with different pitches and circular holes. The results of measurements with these samples will be discussed along with the theoretical investigations.
Previous experiments have shown that surface plasmon polaritons (SPPs) preserve their entangled state and do not cause measurable decoherence. However, essentially all of them were done using SPPs whose dispersion was in the linear “photon-like” regime. We report in this presentation on experiments showing how transition to “true-plasmon” non-linear dispersion regime, which occurs near SPP resonance frequency, will affect quantum coherent properties of light. To generate a polarization-entangled state we utilize type-I parametric down-conversion, occurring in a pair of non-linear crystals (BiBO), glued together and rotated by 90 degrees with respect to each other. For state projection measurements, we use a pair of polarizers and single-photon avalanche diode coincidence count detectors. We interpose a plasmonic hole array in the path of down-converted light before the polarizer. Without the hole array, we measure visibility V=99-100% and Bell’s number S=2.81±0.03. To study geometrical effects we fabricated plasmonic hole arrays (gold on optically polished glass) with elliptical holes (axes are 190nm and 240nm) using focused ion beam. When we put this sample in our system we measured the reduction of visibility V=86±5% using entangled light. However, measurement using classical light gave exactly the same visibility; hence, this reduction is caused only by the difference in transmission coefficients of different polarizations. As samples with non-linear dispersion we fabricated two-layer (a-Si - Au) and three-layer (a-Si – Au – a-Si) structures on optically polished glass with different pitches and circular holes. The results of measurements with these samples will be discussed along with the theoretical investigations.
Plasmonics offers sub-diffraction confinement of light, which affords enhanced coupling to emitter systems (e.g.quantum dots).This feature makes possible a range of on-chip quantum photonic components -most notably single-photon sources and switches.This potential use of plasmonics, along with the nonlinearity provided by emitter systems, opens up quantum plasmonics as a viable route to realising quantum information processing.In this setting, the excitation of single surface plasmon polaritons (SPPs) on waveguides via single photons and the confirmation of single-photon states upon output is an important goal.In the work reported here, plasmonic waveguides were experimentally probed with single photons.A measurement of the secondorder quantum coherence function yielded a value of g (2) (0) = 0.160 ± 0.002.A value less than 0.5 is indicative of single-excitation states.Furthermore, to confirm successful SPP excitation, the transverse-magnetic mode restriction and exponential decay of SPPs were verified.Having firmly established the ability to probe plasmonic waveguides in the classical and quantum regimes, quantum random number generation was implemented using a plasmonic beam splitter.The random bit sequences produced passed the NIST Statisitical Test Suite once post-processed to correct for a slightly asymmetric beamsplitter.
Surface plasmon polaritons (SPPs) are collective excitations of free electrons propagating along a metal-dielectric interface. Although some basic quantum properties of SPPs, such as the preservation of entanglement, the wave-particle duality of a single plasmon, the quantum interference of two plasmons, and the verification of entanglement generation, have been shown, more advanced quantum information protocols have yet to be demonstrated with SPPs. Here, we experimentally realize quantum state teleportation between single photons and SPPs. To achieve this, we use polarization-entangled photon pairs, coherent photon-plasmon-photon conversion on a metallic subwavelength hole array, complete Bell-state measurements and an active feed-forward technique. The results of both quantum state and quantum process tomography confirm the quantum nature of the SPP mediated teleportation. An average state fidelity of [Formula: see text] and a process fidelity of [Formula: see text], which are well above the classical limit, are achieved. Our work shows that SPPs may be useful for realizing complex quantum protocols in a photonic-plasmonic hybrid quantum network.