Mark Tame

Experimental realization of Dicke states of up to six-qubits for multiparty quantum networking

We report the first experimental generation and characterization of a six-photon Dicke state. The produced state shows a fidelity of F=0.56+/-0.02 with respect to an ideal Dicke state and violates a witness detecting genuine six-qubit entanglement by 4 standard deviations. We confirm characteristic Dicke properties of our resource and demonstrate its versatility by projecting out four- and five-photon Dicke states, as well as four-photon Greenberger-Horne-Zeilinger and W states. We also show that Dicke states have interesting applications in multiparty quantum networking protocols such as open-destination teleportation, telecloning, and quantum secret sharing.

Experimental Realization of Deutsch's Algorithm in a One-way Quantum Computer

We report the first experimental demonstration of an all-optical one-way implementation of Deutschs quantum algorithm on a four-qubit cluster state. All the possible configurations of a balanced or constant function acting on a two-qubit register are realized within the measurement-based model for quantum computation. The experimental results are in excellent agreement with the theoretical model, therefore demonstrating the successful performance of the algorithm.

Quantum statistics of surface plasmon polaritons in metallic stripe waveguides.

Heralded single surface plasmon polaritons are excited using photons generated via spontaneous parametric down conversion. The mean excitation rates, intensity correlations, and Fock state populations are studied. The observed dependence of the second-order coherence in our experiment is consistent with a linear uncorrelated Markovian environment in the quantum regime. Our results provide important information about the effect of loss for assessing the potential of plasmonic waveguides for future nanophotonic circuitry in the quantum regime.

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

Optical signals are increasingly used to transfer and process information, because of their high speed, bandwidth, and propagation distances in transparent optical networks. However, the miniaturization of photonic devices faces a hard block: the diffraction limit. One proposed means to go beyond this limit is to use surface plasmons polaritons (SPPs), charge density waves at the interface between a metal and a dielectric, which can be excited with light, as the carrier of the information [1]. It has been demonstrated that SPPs can be confined in sub-wavelength volumes. So far, the study of plasmons has been confined to the classical regime, but recently more attention is given to the quantum regime. Indeed, several interesting devices taking advantage of the large field confinement provided by SPPs have been proposed, such as single photon switches or transistors [2]. However, at this stage, little is known about the behaviour of SPPs in the quantum regime, i.e. when they are excited one at a time for instance. 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 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 [3].

Fusing multipleWstates simultaneously with a Fredkin gate

We propose an optical scheme to prepare large-scale entangled networks of W states. The scheme works by simultaneously fusing three polarization-encoded W states of arbitrary size via accessing only one qubit of each W state. It is composed of a Fredkin gate (controlled-swap gate), two fusion gates [as proposed in New J. Phys. 13, 103003 (2011)] and an H-polarized ancilla photon. Starting with three

Single-Photon Excitation of Surface Plasmon Polaritons

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Robust-to-loss entanglement generation using a quantum plasmonic nanoparticle array

-qubit W states, the scheme prepares a new W state with

Experimental demonstration of graph-state quantum secret sharing

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Experimental Demonstration of Decoherence-Free One-Way Information Transfer

-qubits after postselection if both fusion gates operate successfully, i.e. a four-fold coincidence at the detectors. The proposed scheme reduces the cost of creating arbitrarily large W states considerably when compared to previously reported schemes.

Quantum entanglement distillation with metamaterials.

We provide the quantum-mechanical description of the excitation of surface plasmon polaritons on metal surfaces by single photons. An attenuated-reflection setup is described for the quantum excitation process in which we find remarkably efficient photon-to-surface plasmon wave-packet transfer. Using a fully quantized treatment of the fields, we introduce the Hamiltonian for their interaction and study the quantum statistics during transfer with and without losses in the metal.