Abstract
Quantum plasmonics lies at the intersection between nanophotonics and quantum optics. Genuine quantum effects can be observed with non-classical states such as Fock states and with entangled states. A N00N state combines both aspects: it is a quantum superposition state of a Fock state with N excitations in two spatial modes. Here we report the first observation of two-plasmon (N = 2) N00N state interferences using a plasmonic beamsplitter etched on a planar interface between gold and air. We analyze in detail the role of losses at the beamsplitter and during the propagation along the metal/air interface. While the intrinsic losses of the beamsplitter are responsible for the emergence of quantum nonlinear absorption, we note that N00N states decay N times faster than classical states due to propagation losses.
Highlights
Plasmon–polaritonic waves are the result of strong coupling between light and collective oscillations of electrons that propagate along a metal–dielectric interface [1]
A sum of two sinusoids at λ = 806 nm and λ/2 with the corresponding amplitudes given by the fast Fourier transform (FFT) of the data and with the phase as a free parameter have been plotted in figure 2
The two oscillations can be understood as the expected N00N interference resulting in coincidences oscillating at twice the frequency of the incoming light which are modulated by a residual signal at the frequency of the photons. This residual perturbation of the coincidence fringes is related to a single-particle interference onto the surface plasmon beamsplitter (SPBS)
Summary
Plasmon–polaritonic waves are the result of strong coupling between light and collective oscillations of electrons that propagate along a metal–dielectric interface [1] One of their most interesting feature is the possibility to design plasmonic structures which are able to confine light in sub-diffraction limit volumes. A remarkable feature of confined fields is the fact that even with few photons, a large electric field can be generated so that the light–matter interaction is enhanced and nonlinear effects can be observed In this limit of few photons confined to subwavelength scales, one enters the quantum nanophotonics domain. Recent experimental investigations [2] have shown that many quantum optics experiments can be reproduced using single plasmons They demonstrate that, at some extent, solutions exist to merge the features of field confinement offered by plasmons and the quantum nature of light to perform quantum experiments. Several groups reported methods to generate single plasmons, for example by using a grating to couple single photons to surface plasmons on a metal–dielectric interface [5], or by coupling a single photon emitter to a metallic nanowire [6]
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