arXiv subjects

T. Sweetnam

Publications and source records attributed to T. Sweetnam.

6 recordsLinked to original sources

arXiv2026

A cm-wave quantum noise limited resonant superconducting parametric amplifier

Superconducting Parametric Amplifiers (SPAs) have seen great interest in recent years due to their high gain and quantum limited noise performance. Among these amplifiers, resonant SPAs have been widely developed for experiments where ultra low-noise narrow-band amplification is of interest, such as the search for Axion dark matter in particle physics and the detection of spectroscopic lines in astrophysics, while also finding applications in quantum computing. This work presents an amplifier based on a Complementary Split Ring Resonator (CSRR), patterned on a NbTi coated sapphire substrate embedded within a waveguide, designed to work at a set of four narrow frequency bands throughout K band (18-27 GHz) using the kinetic inductance of the superconducting film. The S-parameters measured at 400 mK, using a sorption cooler, show the four resonances between 23.3 and 26.3 GHz at 1 GHz spacing, with a maximum transmission on resonance of -1 dB. Four-wave mixing has been observed with each resonance, and a maximum signal gain of 30 dB has been measured, corresponding to 29 dB of insertion gain. The noise performance of the amplifier has been measured, showing an added noise of 1.2 half quanta at 400 mK. These results are relevant to high-frequency Axion dark matter experiments and help motivate the exploration of higher frequencies in quantum technologies.

physics.ins-det↗

arXiv2024

In-operando microwave scattering-parameter calibrated measurement of a Josephson travelling wave parametric amplifier

Superconducting travelling wave parametric amplifiers (TWPAs) are broadband near-quantum limited microwave amplifiers commonly used for qubit readout and a wide range of other applications in quantum technologies. The performance of these amplifiers depends on achieving impedance matching to minimise reflected signals. Here we apply a microwave calibration technique to extract the S-parameters of a Josephson junction based TWPA in-operando. This enables reflections occurring at the TWPA and its extended network of components to be quantified, and we find that the in-operation performance can be well described by the off-state measured S-parameters.

quant-ph↗

arXiv2022

Simulating the behaviour of travelling wave superconducting parametric amplifiers using a commercial circuit simulator

Kinetic inductance travelling wave parametric amplifiers (KI-TWPAs) have been simulated using Keysight's Advanced Design System (ADS). A lumped element representation of a superconducting transmission line has been developed using nonlinear inductor elements to represent the current dependency of the intrinsic kinetic inductance. This provides a fast, simple and easily modifiable method for analysing the parametric processes that occur in nonlinear kinetic inductance devices such as parametric oscillators or amplifiers, while also allowing the accompanying RF network to be optimised. This methodology is used to model the behaviour of a select number of KI-TWPA designs operating in the 3-wave mixing (3WM) and 4-wave mixing (4WM) regimes. S-parameters and dispersion properties are extracted from large signal S-parameter simulations and the gain curve of each amplifier design is generated from harmonic balance simulations. Results of these are compared to the gain expression from the analytic solutions of the coupled mode equations, while making reference to the gain curves of the equivalent KI-TWPAs from literature.

cond-mat.supr-con↗

arXiv2021

Australian Square Kilometre Array Pathfinder: I. System Description

In this paper we describe the system design and capabilities of the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope at the conclusion of its construction project and commencement of science operations. ASKAP is one of the first radio telescopes to deploy phased array feed (PAF) technology on a large scale, giving it an instantaneous field of view that covers 31 square degrees at 800 MHz. As a two-dimensional array of 36x12m antennas, with baselines ranging from 22m to 6km, ASKAP also has excellent snapshot imaging capability and 10 arcsecond resolution. This, combined with 288 MHz of instantaneous bandwidth and a unique third axis of rotation on each antenna, gives ASKAP the capability to create high dynamic range images of large sky areas very quickly. It is an excellent telescope for surveys between 700 MHz and 1800 MHz and is expected to facilitate great advances in our understanding of galaxy formation, cosmology and radio transients while opening new parameter space for discovery of the unknown.

astro-ph.IM↗

arXiv2015

Discovery of HI gas in a young radio galaxy at $z = 0.44$ using the Australian Square Kilometre Array Pathfinder

We report the discovery of a new 21-cm HI absorption system using commissioning data from the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP). Using the 711.5 - 1015.5 MHz band of ASKAP we were able to conduct a blind search for the 21-cm line in a continuous redshift range between $z = 0.4$ and 1.0, which has, until now, remained largely unexplored. The absorption line is detected at $z = 0.44$ towards the GHz-peaked spectrum radio source PKS B1740$-$517 and demonstrates ASKAP's excellent capability for performing a future wide-field survey for HI absorption at these redshifts. Optical spectroscopy and imaging using the Gemini-South telescope indicates that the HI gas is intrinsic to the host galaxy of the radio source. The narrow OIII emission lines show clear double-peaked structure, indicating either large-scale outflow or rotation of the ionized gas. Archival data from the \emph{XMM-Newton} satellite exhibit an absorbed X-ray spectrum that is consistent with a high column density obscuring medium around the active galactic nucleus. The HI absorption profile is complex, with four distinct components ranging in width from 5 to 300 km s$^{-1}$ and fractional depths from 0.2 to 20 per cent. In addition to systemic HI gas, in a circumnuclear disc or ring structure aligned with the radio jet, we find evidence for a possible broad outflow of neutral gas moving at a radial velocity of $v \sim 300$ km s$^{-1}$. We infer that the expanding young radio source ($t_{\rm age} \approx 2500$ yr) is cocooned within a dense medium and may be driving circumnuclear neutral gas in an outflow of $\sim$ 1 $\mathrm{M}_{\odot}$ yr$^{-1}$.

astro-ph.GA↗

arXiv2014

The Australian Square Kilometre Array Pathfinder: System Architecture and Specifications of the Boolardy Engineering Test Array

This paper describes the system architecture of a newly constructed radio telescope - the Boolardy Engineering Test Array, which is a prototype of the Australian Square Kilometre Array Pathfinder telescope. Phased array feed technology is used to form multiple simultaneous beams per antenna, providing astronomers with unprecedented survey speed. The test array described here is a 6-antenna interferometer, fitted with prototype signal processing hardware capable of forming at least 9 dual-polarisation beams simultaneously, allowing several square degrees to be imaged in a single pointed observation. The main purpose of the test array is to develop beamforming and wide-field calibration methods for use with the full telescope, but it will also be capable of limited early science demonstrations.

astro-ph.IM↗