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We experimentally study surface plasmon lasing in a series of metal hole arrays on a gold-semiconductor interface. The sub-wavelength holes are arranged in square arrays of which we systematically vary the lattice constant and hole size. The semiconductor medium is optically pumped and operates at telecom wavelengths (λ ~ 1.5 μm). For all 9 studied arrays, we observe surface plasmon (SP) lasing close to normal incidence, where different lasers operate in different plasmonic bands and at different wavelengths. Angle- and frequency-resolved measurements of the spontaneous emission visualizes these bands over the relevant (ω, k||) range. The observed bands are accurately described by a simple coupled-wave model, which enables us to quantify the backwards and right-angle scattering of SPs at the holes in the metal film.

We perform quantum state reconstruction of coherent and thermal states with a detector which has an enhanced multiphoton response. The detector is based on superconducting nanowires, where the bias current sets the dependence of the click probability on the photon number; this bias current is used as tuning parameter in the state reconstruction. The nonlinear response makes our nanowire-based detector superior to the linear detectors that are conventionally used for quantum state reconstruction., Comment: revision of intro compared to V1

Using detector tomography, we investigate the detection mechanism in NbN-based superconducting single photon detectors (SSPDs). We demonstrate that the detection probability uniquely depends on a particular linear combination of bias current and energy, for a large variation of bias currents, input energies and detection probabilities, producing a universal detection curve. We obtain this result by studying multiphoton excitations in a nanodetector with a sparsity-based tomographic method that allows factoring out of the optical absorption. We discuss the implication of our model system for the understanding of meander-type SSPDs., Comment: Revised version

We present an experimental method to characterize multi-photon detectors with a small overall detection efficiency. We do this by separating the nonlinear action of the multiphoton detection event from linear losses in the detector. Such a characterization is a necessary step for quantum information protocols with single and multiphoton detectors and can provide quantitative information to understand the underlying physics of a given detector. This characterization is applied to a superconducting multiphoton nanodetector, consisting of an NbN nanowire with a bowtie-shaped subwavelength constriction. Depending on the bias current, this detector has regimes with single and multiphoton sensitivity. We present the first full experimental characterization of such a detector.

We report an experimental test of the photodetection mechanism in a nanowire superconducting single photon detector. Detector tomography allows us to explore the 0.8-8 eV energy range via multiphoton excitations. High accuracy results enable a detailed comparison of the experimental data with theories for the mechanism of photon detection. We show that the temperature dependence of the efficiency of the superconducting single photon detector is determined not by the critical current but by the current associated with vortex unbinding. We find that both quasiparticle diffusion and vortices play a role in the detection event.