High-contrast dispersive readout of a superconducting flux qubit using a nonlinear resonator

Applied Science

Asymmetry reversal and waveguide modes in photonic crystal slabs

The measured reflection spectra of two-dimensional photonic crystal slabs consist of an asymmetric peak on top of an oscillating background. For p-polarized light, the asymmetry of the peak flips for angles of incidence beyond Brewster’s angle. We explain the observed line shapes with a Fano model that includes loss and use a waveguide model to predict the resonance frequencies of the photonic crystal slab. Finite-difference time domain calculations support the model and show that the resonance due to a higher order mode disappears when the substrate refractive index is increased beyond ns = 2.04. This is readily explained by the cut-off condition of the modes given by the waveguide model.NanofacilityApplied Science

Low-frequency noise in Josephson junctions for superconducting qubits

The authors have studied low-frequency resistance fluctuations in shadow-evaporated Al/AlOx/Al tunnel junctions. Between 300 and 5?K the spectral density follows a 1/f law. Below 5?K, individual defects distort the 1/f shape of the spectrum. The spectral density decreases linearly with temperature between 150 and 1?K and saturates below 0.8?K. At 4.2?K, it is about two orders of magnitude lower than expected from a recent survey [D. J. Van Harlingen et al., Phys. Rev. B 70, 064510 (2004)]. Due to saturation below 0.8?K the estimated qubit dephasing times at 100?mK are only about two times longer than calculated by Van Harlingen et al.Kavli Institute of NanoscienceApplied Science

Fabrication and performance verification of a 961 pixel Kinetic Inductance Detector system for future space borne observatories 9914-138

Astronomical observations at infrared, sub-millimetre, and millimetre wavelengths are essential for addressing many of the key questions in astrophysics. Future ground- and space based observatories need large detector arrays with a sensitivity limited only by the noise of the radiation background. We demonstrate that antenna coupled Microwave Kinetic Inductance Detectors allow us to create kpixel large arrays with background limited sensitivity over the entire FIR/mmwavelength range. We discuss in detail the readout system and experimental results of a 961 pixel array, optimised for 850 GHz radiation that is read out with a single readout chain.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz SensingQN/Quantum NanoscienceQN/Mol. Electronics & Device

A kilo-pixel imaging system for future space based far-infrared observatories using microwave kinetic inductance detectors

Aims. Future astrophysics and cosmic microwave background space missions operating in the far-infrared to millimetre part of the spectrum will require very large arrays of ultra-sensitive detectors in combination with high multiplexing factors and efficient low-noise and low-power readout systems. We have developed a demonstrator system suitable for such applications. Methods. The system combines a 961 pixel imaging array based upon Microwave Kinetic Inductance Detectors (MKIDs) with a readout system capable of reading out all pixels simultaneously with only one readout cable pair and a single cryogenic amplifier. We evaluate, in a representative environment, the system performance in terms of sensitivity, dynamic range, optical efficiency, cosmic ray rejection, pixel-pixel crosstalk and overall yield at an observation centre frequency of 850 GHz and 20% fractional bandwidth. Results. The overall system has an excellent sensitivity, with an average detector sensitivity (NEPdet) =3 × 10-19 W/Hz measured using a thermal calibration source. At a loading power per pixel of 50 fW we demonstrate white, photon noise limited detector noise down to 300 mHz. The dynamic range would allow the detection of ~1 Jy bright sources within the field of view without tuning the readout of the detectors. The expected dead time due to cosmic ray interactions, when operated in an L2 or a similar far-Earth orbit, is found to be <4%. Additionally, the achieved pixel yield is 83% and the crosstalk between the pixels is <-30 dB. Conclusions. This demonstrates that MKID technology can provide multiplexing ratios on the order of a 1000 with state-of-the-art single pixel performance, and that the technology is now mature enough to be considered for future space based observatories and experiments.Tera-Hertz SensingQN/Quantum NanoscienceQN/Gao La