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.
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.
This thesis investigates properties of quantum states of light while travelling as surface plasmon polaritons in plasmonic waveguides and structures. The bosonic nature of SPPs has been shown in previous work by performing a Hong-Ou-Mandel interference experiment with a plasmonic scattering-based beam splitter. Here, we show the same interference with a higher statistical power thanks to an improved set-up. A visibility of 59 ± 1 % is obtained in the two-photon interference, clearly breaking the classical limit of 50 %. The importance of the phase-relations between the different modes in the beam splitter is experimentally probed. The output state of the interference is then further analyzed by a quantum state tomography set-up. This makes it possible to quantify the entanglement generated in the interference. As the interference happens in the plasmonic beam splitter, this shows, to our knowledge for the first time, entanglement generated in a plasmonic structure. Together with the recent results in terms of entanglement and coherence preservation of SPPs, this clearly shows the potential of quantum plasmonic devices. To move into the realm of applications, we also investigate theoretically the enhancements in sensitivity quantum states of light can deliver for plasmonic sensing. It is shown that despite the losses, quantum metrology techniques can be useful in an interferometer with plasmonic waveguides. Considering the strengths and successes of plasmonic sensing techniques in a wide range of fields, we envision that entangled and squeezed states of light will become a new route to push the limits in sensitivity.
Abstract We report an experimental realisation of a quantum random number generator using a plasmonic beamsplitter. Free-space single photons are converted into propagating single surface plasmon polaritons on a gold stripe waveguide via a grating. The surface plasmons are then guided to a region where they are scattered into one of two possible outputs. The presence of a plasmonic excitation in a given output determines the value of a random bit generated from the quantum scattering process. Using a stream of single surface plasmons injected into the beamsplitter we achieve a quantum random number generation rate of 2.37 Mbits s −1 even in the presence of loss. We characterise the quality of the random number sequence generated, finding it to be comparable to sequences from other quantum photonic-based devices. The compact nature of our nanophotonic device makes it suitable for tight integration in on-chip applications, such as in quantum computing and communication schemes.
Light-matter interactions underlie many quantum technologies, yet whether quasiparticles formed from such interactions preserve the full quantum state of light remains unresolved. Surface plasmon polaritons (SPPs), a class of polaritons formed by interacting photons with free-electron oscillations at metal-dielectric interfaces, are prime candidates to explore this question. Here we demonstrate quantum interference between single photons and SPPs using an Au-SiNx integrated photonic-plasmonic device. Our results reveal that SPPs retain the indistinguishability of their excitation photons, establishing SPP as a viable quantum information carrier and opening a potential route toward photonic-plasmonic quantum circuitry.
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.
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.
Quantum walks (QWs) simulate particle behaviors in the quantum mechanical regime, which exhibit time evolutions completely different from the classical (probabilistic) random works [1]. QWs offer quantum physical simulations and the novel approach to build quantum computers. Currently on-chip photonic devices implementing QWs have been intensively developed. QW photonic chips were realized using photonic circuits based on silica (SiO2) waveguide platforms [1,2]. Here, we demonstrate a QW chip based on the other waveguide platform, namely the long-range surface plasmon polariton (LR-SPP) waveguide [3]. The LR-SPP waveguide allows a single-polarization mode, and has relatively low optical losses. Moreover, the LR-SPP waveguide platform will realize two-dimensional waveguide lattice structures with a high reliability. Thus, the LR-SPP waveguide is the potential platform to construct large-scale and high-dimension QW simulators.