Superconducting quantum detectors

Abstract:

We report the development of an on-chip, compact dual-polarisation Superconductor-Insulator-Superconductor (SIS) receiver covering the millimetre frequency band from 190 GHz to 290 GHz. All the required components for the receiver are integrated on-chip using planar circuit technology, except the feedhorn. We use a 4-probe orthomode transducer (OMT) to couple the radio frequency (RF) and local oscillator (LO) and to split the incoming signal into two RF polarisation states before they are routed to the twin junction Nb/A10x/Nb mixers via a planar crossover, branch-line hybrids and bandpass filters. The entire receiver chip, only 4.0 mm by 4.1mm in size, is mounted in a split block where the feedhorn and the magnetic biasing are located on the front side, and the intermediate frequency (IF) and DC biasing connectors are on the rear side, leaving the four adjacent sides of the block unobscured for a 2-dimensional extension into a multi-pixel array. In this paper, we present the receiver and mixer block design and preliminary experimental results obtained from testing the receiver.

Abstract:

Abstract We are standing at the crossroads of powerful new facilities emerging in the next decade on the ground and in space like ELT, SKA, JWST, and Athena. Turning the narrative of the star formation potential of galaxies into a quantitative theory will provide answers to many outstanding questions in astrophysics, from the formation of planets to the evolution of galaxies and the origin of heavy elements. To achieve this goal, there is an urgent need for a dedicated space-borne, far-infrared spectroscopic facility capable of delivering, for the first time, large scale, high spectral resolution (velocity resolved) multiwavelength studies of the chemistry and dynamics of the ISM of our own Milky Way and nearby galaxies. The Far Infrared Spectroscopic Surveyor (FIRSS) fulfills these requirements and by exploiting the legacy of recent photometric surveys it seizes the opportunity to shed light on the fundamental building processes of our Universe.

Abstract:

In this paper, we present a method to measure the effective physical temperature of the tunnel junction in a terahertz superconductor-insulator-superconductor (SIS) mixer when illuminated with a strong local oscillator (LO) power that results in local hot spot around the tunnel junction. We observed that the gap voltage of the pumped current-voltage (IV) curve is suppressed when the LO pumping level is increased, indicating that the junction physical temperature is increased beyond the mixer block temperature. We quantified this extra heating effect by recovering the effective junction temperature through comparing the gap voltage of the pumped IV curves measured at a fixed block temperature, with the unpumped IV curve measured at varying block temperatures. We found that the heat trapped in the tunnel junction can be as high as 1.7 K when the mixer stabilised at 3.3 K is pumped at only 21% of the gap current.

Abstract:

We present a new approach to develop a Josephson Junction Travelling Wave Parametric Amplifier (JTWPA) that could potentially minimise the gain-ripple effect. Our design consists of a 50 Ω superconducting niobium coplanar waveguide (CPW) periodically loaded with series of Josephson junctions (JJs) to provide the non-linearity required for wave mixing. The embedded JJs alter the characteristic impedance of the transmission line abruptly, therefore creating the stopbands in the transmission (S21) for the suppression of higher harmonics and provide the means for dispersion engineering required to achieve exponential gain. The simulated gain profile of the amplifier shows that we can obtain a minimum of 15 dB gain from 4–12 GHz, close to a 100% bandwidth performance. More importantly, the characteristic impedance of the main linear transmission line remains unaffected by the strong pump, therefore ensuring the TWPA remains impedance matched to the input and output ports. This can reduce the unwanted gain undulation that inflict the optimal performance of the TWPA.