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19 th International Symposium on Space Terahertz Technology Antenna-coupled Microwave Kinetic Inductance detectors (MKIDs) for mm and submm imaging arrays. 5-3 A. Vayonakis, J. Schlaerth, S. Kumar, J.-S. Gao, P. Day, B. Mazin, M. Ferry, O. Noroozian, J. Glenn, S. Golwala, H. LeDuc, J. Zmuidzinas We present results from completely lithographic antenna-coupled Microwave Kinetic Inductance detectors (MKIDs). MKIDs are superconducting resonators with resonant frequency and quality-factor which are highly sensitive to changes in the density of the quasiparticle population which occurs when photons above the superconducting gap energy are absorbed. The resonators are coupled to submm light through on-chip phasedarray slot antennas. Each planar antenna consists of an array of N long slots which are fed along their length at M points. The resulting N*M feed points are combined in-phase using a binary summing tree made of low-loss superconducting microstrip lines. Due to its large size, the resulting planar antenna produces a narrow beam pattern and can therefore be used without additional optical coupling elements such as feedhorns or substrate lenses. The output of the antenna is a single superconducting thin-film microstrip line which can be efficiently coupled to one (or more) kinetic inductance coplanar waveguide resonators to produce a single (or multi-color) pixel in an imaging focal plane array, using in-line lumped element lithographic band-pass filters. Such highly integrated architectures can be easily fabricated on a single substrate, and many detectors can be frequency multiplexed through coupling to a single feedline. Microwave readout provides a lot of bandwidth per detector, allowing a large number of pixels to be read using a single cryogenic microwave amplifier and warm readout electronics. We show results from a demonstration camera (DemoCam) using MKIDs. This camera features 16 planar antennas on its focal plane, each feeding two MKID resonators through in-line bandpass filters with bands centered at 240 GHz and 350 GHz. 48
19 th International Symposium on Space Terahertz Technology 5-4 Contribution of dielectrics to frequency and noise of NbTiN superconducting resonators R. Barends 1 , H. L Hortensius 1 , T. Zijlstra 1 , J. J. A. Baselmans 2 , S. J. C. Yates 2 , J. R. Gao 1,2 , and T. M. Klapwijk 1 1 Kavli Institute of NanoScience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands 2 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands The low temperature microwave properties of superconducting resonators for kinetic inductance photon detectors [1] and quantum computation [2] are attracting increased attention. At low temperatures both a significant excess frequency noise and deviations in the resonance frequency from Mattis-Bardeen theory have been found. It has been suggested that these anomalies are caused by dipole two-level systems residing in dielectric layers near surfaces, which interact with the high frequency electric fields in the resonator [3-4]. In order to identify to what extent two-level systems in dielectrics affect the microwave properties of superconducting films we study NbTiN resonators with a 10, 40 or 160 nm thick SiO2 covering layer. We find that the resonance frequency of bare NbTiN resonators, unlike Nb, Ta and Al resonators, closely follows Mattis-Bardeen theory down to 350 mK. We demonstrate that deviations in the resonance frequency can be generated by covering the resonators with a thin amorphous SiO2 layer, and that these deviations scale with the layer thickness. In addition, we find that the frequency noise is strongly increased as soon as a SiO2 layer is present, but is, counter-intuitively, independent of the layer thickness. These observations show that the physical mechanisms causing the excess frequency noise are different from those responsible for the deviations in the resonance frequency. [1] P. K. Day et al., Nature 425, 817 (2003). [2] A. Wallraff et al., Nature 431, 162 (2004). [3] J. Gao et al., Appl. Phys. Lett. 90, 102507 (2007). [4] J. Gao et al., arXiv:0802.4457. 49
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