Superconducting quantum detectors

Abstract:

Travelling wave parametric amplifiers (TWPAs) made from highly nonlinear reactive superconducting thin films have been demonstrated to be a potentially viable quantum-noiselimited amplifier technology for various fundamental physics platforms, including microwave/millimetre (mm)/sub-mm astronomy, dark matter search experiments, absolute neutrino mass determinations, and qubit readout platforms. To date, only a limited number of successful kinetic inductance (KI-)TWPA devices have been reported, with the majority of them fabricated from niobium titanium nitride (NbTiN) thin films; although in principle, any highly nonlinear low loss superconducting film can be used to construct a KITWPA. In this proceeding, we explore the suitability of using a different type of superconducting film, titanium nitride (TiN) for such application. We report on the detailed analysis of the nonlinear behaviour of TiN films to ascertain the film’s suitability for application as KITWPA. We experimentally characterised TiN transmission lines at cryogenic temperatures to compare the results predicted with electromagnetic simulations. This characterisation and analysis allows us to understand the fundamental physics governing the behaviour of the TiN films, their merits and limitations, and whether they are well suited for applications as KITWPAs.

Abstract:

Superconducting On-chip Fourier Transform Spectrometers (SOFTS) are broadband, ultra-compact and electronic interferometers. SOFTS will enable kilo-pixel spectro-imaging focal planes, enhancing sub-millimeter astrophysics and cosmology. Particular applications include cluster astrophysics, cosmic microwave background (CMB) science, and line intensity mapping. This article details the development, design and bench-marking of radio frequency (RF) on-chip architecture of SOFTS for Ka and W-bands.

Abstract:

We present and compare the design and performance of two 850 GHz radial probe fed superconductor-insulator-superconductor mixers, where the antenna is aligned perpendicular to the E-Plane of the input full-height rectangular waveguide connected to a multiple flare-angles smooth-walled horn. Both designs are comprised of 0.5 µm2 hybrid niobium/aluminium-nitride/niobium-nitride tunnel junction, fabricated on top of a niobium titanium nitride ground plane with an Al wiring layer. The entire superconducting circuit is supported with a 40 µm thick quartz substrate. The major difference between the two designs is the method used to cancel out the parasitic junction capacitance for broadband performance. The first design utilises two identical junctions connected in parallel with a short transmission line to convert the capacitance of one junction into the equivalent inductance of the other junction, commonly known as the twin-junction tuning scheme; whilst the second design employs an end-loaded scheme with only one tunnel junction. We found that both methods offer similar radio frequency performances, with close to 2× the double sideband quantum noise temperature, but the twin-junction design is more resilient to fabrication tolerances. However, the end-loaded design offers a much better intermediate frequency (IF) bandwidth performance, made possible by the sub-micron and high current density tunnel junction technology. The improved IF performance is important for many millimetre (mm) and sub-mm observatories, such as future upgrades of Atacama Large Millimetre/sub-mm Array receivers, as well as forthcoming space-borne far-infrared missions. Therefore, we conclude that the single-junction mixer design is the preferred option for THz applications, as long as the fabrication error can be minimised within a certain limit

Abstract:

Travelling wave parametric amplifiers (TWPAs) made from highly non-linear reactive superconducting thin films have been demonstrated to be a potentially viable quantum-noise-limited amplifier technology for various fundamental physics platforms, including microwave/mm/sub-mm astronomy, dark matter search experiments, neutrino mass experiments, and qubit readout. We present a kinetic inductance TWPA consisting of a patterned titanium nitride film on a sapphire substrate, which comprises a coplanar waveguide (CPW) with a continuous, smoothed periodic loading (PL) structure that modulates the characteristic impedance of the CPW in a double sinusoidal fashion. This double sinusoidal modulation creates much stronger dispersion features than a conventional PL design, which allows for phase matching and pump harmonic suppression over a much shorter transmission length, potentially leading to reduced losses. In this paper, we shall discuss in detail the design of our TWPA and present the predicted gain-bandwidth characteristics from electromagnetic simulations.