Josephson Junctions and Cosmic Microwave Background

Thomas F. Finnegan, S. Wahlstent

K. Hattori, M. Hazumi, H. Ishino +11 more

We present our recent development of superconducting detectors for measurements of cosmic microwave background. We have fabricated antenna-coupled superconducting tunnel junctions (STJs). Two different types of STJs have been fabricated: the parallel-connected twin junction and the microstrip. Both types of STJs made of Nb and Al have successfully detected 80 GHz millimeter wave radiation with photon-assisted tunneling. We have also developed microwave kinetic inductance detectors (MKIDs). The MKIDs offer us high multiplexing factors with a single readout line using the frequency-domain readout. We have developed abosrption-type and transmission-type MKIDs whose resonators are formed with either coplanar waveguides (CPW) or microstrips. The quality factor of the CPW MKID made of Nb is measured to be about 105. The microstrip MKID is being developed for the multichroic measurements.

Alex Stephane Piedjou Komnang, Claudio Guarcello, C. Barone +2 more

This work deals with the numerical analysis of the zero-voltage state lifetimes distribution of an underdamped Josephson junction used for the detection of single microwave photons in the presence of thermal noise. The analysis considers the switching probabilities of a JJ subjected to a train of current pulses, which simulates a weak photon field. To characterize the detection, we take advantage of a statistic tool, the Kumar-Carroll (KC) index, which is a good proxy of the signal-to-noise-ratio. It can be, therefore, exploited to identify the proper device fabrication parameters and the optimal operation point of the junction.

Kazuhiro Yoshida, K. Hamasaki, Fumi Irie +1 more

Junji Inatani

Matías Rolf Hampel, L.P. Ferreyro, Oliver Kieler +17 more

Microwave SQUID multiplexers (μMUX) have become a key technology for the readout of large arrays of low-temperature detectors, particularly in cosmic microwave background experiments. A critical element of this technique is the flux-ramp modulation signal, whose noise, especially at low frequencies, directly limits the readout performance. This work proposes and experimentally demonstrates the use of a Josephson Arbitrary Waveform Synthesizer (JAWS) as a low-noise, high precision source for generating the sawtooth-shaped flux-ramp signal required in μMUX readout systems. The JAWS, based on the AC Josephson effect, provides intrinsically quantized and spectrally pure waveforms with excellent signal-to-noise ratio. The operation of a 9000-junction JAWS array is characterized and integrated with a cryogenic μMUX device and a custom SDR-based readout system. With this setup, the noise floor level around the harmonic typically used for phase demodulation of the SQUID signal to recover the detector signal was −104dBc/Hz, and the signal-to-noise ratio of this harmonic was 73dB. These results demonstrate the feasibility of using JAWS-based waveform synthesis for μMUX flux-ramp generation.