Clément Dumesnil : Direct detection of surface plasmon polaritons by a kinetic inductance detector

Surface plasmon polaritons (SPPs) are promising candidates to bridge nanoscale electronics and optics, owing to their subwavelength confinement and their ability to be guided on-chip. Potential applications include compact high-speed optoelectronic components and, more prospectively, interfaces for integrated quantum technologies. Their detection, however, has long relied on far-field optics, either through radiative leakage into a glass substrate, as in surface plasmon resonance experiments, or through scattering by the roughness of the plasmonic metal. Over the past two decades, progress has been made towards the electrical detection of SPPs, which allows them to be detected directly on-chip without resorting to far-field collection. In this work, we present a new on-chip SPP detector based on kinetic inductance detectors (KIDs), superconducting microwave resonators already used for photon detection in astronomy. Our device relies on hybrid NbTiN/Al quarter wave coplanar waveguide resonators, in which aluminum acts both as the plasmonic material and as the absorber : SPPs launched by a grating coupler illuminated with a 1550 nm laser propagate along the aluminum and are detected by the resonator through Cooper pair breaking and the resulting change in its surface impedance. Taking advantage of the frequency multiplexing offered by microwave resonators, several KIDs placed at different distances from the grating are probed simultaneously on a single readout line, which allows us to measure an SPP propagation length of about 100 µm. In addition, scanning a pulsed laser along the resonators provides a position-resolved injection of quasiparticles in the aluminum. The time-resolved response then gives access to the quasiparticle dynamics, namely recombination and diffusion, and to the spatial sensitivity of the detector, which follows the current distribution of the resonant mode. This work opens up new experimental possibilities for plasmonic circuitry, such as the simultaneous characterization of many plasmonic elements through frequencymultiplexed detection, and paves the way towards the integration o