In this study, we present our experimental results on the optical, magnetic, as well as magneto-optic properties of hexagonal arrays of subwavelength holes in optically thin cobalt films. Different meshes were used with hole diameters ranging between 220 and 330 nm while the interhole distance has been kept constant at 470 nm. The hole pattern modifies completely the magnetic behavior of the cobalt films; it gives rise to an increase of the coercive field of the in-plane magnetization with increasing hole diameter and to the appearance of out-of-plane magnetization components. Magneto-optic measurements show a spectacular magneto-optic response at wavelengths where surface plasmon-polaritons are supported by the structure as deduced in optical measurements. The experiments demonstrate the ability to artificially control the magnetic and thus the magneto-optic properties in hole array structures.

We investigate two-photon quantum interference in an opaque scattering medium that intrinsically supports 10 6 transmission channels. By adaptive spatial phase-modulation of the incident wavefronts, the photons are directed at targeted speckle spots or output channels. From 10 3 experimentally available coupled channels, we select two channels and enhance their transmission, to realize the equivalent of a fully programmable 2 × 2 beam splitter. By sending pairs of single photons from a parametric down-conversion source through the opaque scattering medium, we observe two-photon quantum interference. The programmed beam splitter need not fulfill energy conservation over the two selected output channels and hence could be non-unitary. Consequently, we have the freedom to tune the quantum interference from bunching (Hong-Ou-Mandel-like) to antibunching. Our results establish opaque scattering media as a platform for high-dimensional quantum interference that is notably relevant for boson sampling and physical-key-based authentication.PACS numbers: 42.50. Dv, 42.25.Dd, 42.50.Ex Light waves propagating through an opaque scattering medium exhibit a random walk inside the medium, which is caused by multiple scattering from spatial inhomogeneities [1]. An alternative description describes this by a transmission matrix [2,3]. The transmission matrix describes how a large amount of input channels is coupled to a similarly large amount of output channels, see Fig. 1. The number of these channels can be controlled, and easily made to exceed millions, by increasing the illuminated area on the medium. Recent advances in control of light propagation through complex wavefront shaping allow for complete control over these channels in multiple-scattering media [3][4][5]. Because of their large number of controllable channels, we explore the use of multiple-scattering media to study quantum interference between multiple photons. Employed as a platform for highdimensional quantum interference, over a large number of channels, multiple-scattering media are of relevance to boson sampling [6][7][8][9][10][11][12][13][14], quantum information processing [15][16][17][18], and physical-key-based authentication [19].It has previously been observed that quantum states are robust against multiple scattering. Correlations in two-photon speckle patterns in single-scattering media have been studied [20,21]. Further, propagation of quantum noise [22][23][24] and propagation of single-photon Fock states through multiplescattering media [25,26] have also been explored. So far it has remained an open question if quantum interference of multiple photons could be demonstrated inside a multiplescattering medium. A hurdle one might expect in an experimental implementation is the low transmission of almost all channels in the multiple-scattering medium. Remarklably, the transmission per channel is not necessarily low since complex wavefront shaping allows funneling of light into selected output modes [3,5].Here we report on an experiment in which we...

We have studied the light transmission through hexagonal arrays of subwavelength holes in thin gold and aluminum films, varying the film thickness between 20 and 120 nm while the hole diameter as well as the interhole distance have been kept constant at approximately 300 and approximately 500 nm, respectively. The films were characterized by means of UV-vis spectroscopy and scanning near-field optical microscopy (SNOM).

We have studied a GaAs-AlAs planar microcavity with a resonance near 1300 nm in the telecom range by ultrafast pump-probe reflectivity. By the judicious choice of pump frequency, we observe a ultimate fast and reversible decrease of the resonance frequency by more than half a linewidth due to the instantaneous electronic Kerr effect. The switch-on and switch-off of the cavity is only limited by the cavity storage time of τ cav = 0.3ps and not by intrinsic material parameters. Our results pave the way to supra-THz switching rates for on-chip data modulation and real-time cavity quantum electrodynamics.Switches are widely applied and necessary ingredients in modulation and computing schemes 1 . The recent progress on photonic integrated circuits 2,3 promises to overtake boundaries set by conventional switching technology. To do so, ultrafast switching of photonic cavities is crucial as it allows the capture or release on demand of photons 4-6 , which is relevant to on-chip communication with light as information carrier 7 , and to high-speed miniature lasers 8 . Ultrafast switching would also permit the quantum electrodynamical manipulation of coupled cavity-emitter systems 9 in real-time. Switching the optical properties of photonic nanostructures is achieved by changing the refractive index of the constituent materials. To date, however, the switching speed has been limited by material properties 11-14 , but not by optical considerations. To achieve ultimate fast switching of a cavity two challenges arise. Firstly, both the switch-on and switch-off times τ on and τ of f must be shorter than all other relevant time scales for the system, i.e., the cavity storage time in photon capture/release experiments τ cav , or the vacuum Rabi period τ Rabi for a strongly coupled emitter-cavity system 10 . Secondly, the refractive index change must be large enough to switch the cavity resonance by at least half a linewidth.Here, we demonstrate the ultimate fast switching of the resonance of a planar cavity in the well-known GaAs/AlAs system in the telecom wavelength range. We exploit the instantaneously fast electronic Kerr effect by the judicious tuning of the pump and probe frequencies relative to the semiconductor bandgap. We observe that the speed of the switching is then only limited by the dynamics of the light in our cavity (τ cav = 0.3 ps), but not by the intrinsic material parameters.Instantaneous on-and off-switching with vanishing τ on and τ of f is feasible with the well-known nonlinear rea) Electronic mail: g.ctistis@utwente.nl b) Electronic mail: W.L.Vos@tnw.utwente.nl fractive index from nonlinear optics 15 . Physically the electronic Kerr effect is the fastest Kerr phenomenon on account of the small electron mass. In many practical situations, however, non-degenerate two-photon absorption overwhelms any instantaneous effect and therefore also the dispersive electronic Kerr effect 13,15 . In order to avoid two-photon absorption and to access the electronic Kerr switching regime, we designed our experiment to op...