Millimetre-Wave Superconducting Quantum Amplifiers for Radio Astronomy

Amplification of weak signals with high sensitivity is almost exclusively achieved using high electron mobility transistor (HEMT) amplifiers. They are an integral part of the most highly-sensitive instruments for astronomy, quantum computing, Earth observation and low-temperature physics. HEMT amplifiers however have fundamental drawbacks. The sensitivity is still beyond what can be achieved, to approach the quantum limited level. They are power hungry, requiring substantial heat dissipation, and both the noise temperature and bandwidth deteriorate rapidly at higher frequencies. There is therefore an intense interest for developing a new amplifier technology with quantum-limited noise performance, high gain over wide bandwidths, ultra-low power dissipation and capable to operate in the millimetre (mm) and sub-mm wavelength regime.

The emerging technology of superconducting parametric amplifiers (SPAs) has the potential to achieve all these requirements. Amplification is achieved by varying the device reactance via a strong 'pump' wave that would allow power transfer from the strong pump to the weak signal. Because the process relies purely on superconducting nonlinear reactive response, dissipation is exceedingly small, therefore allowing the quantum limit to be achieved. They are also small in size, robust and very versatile with high fabrication yield.

Most published work in this area described SPAs that could operate only at microwave frequencies. This PhD project aims to develop a wideband SPA that would operate at millimetre wave regime as pre-amplifier for the quantum mixers developed for radio, mm and sub-mm astronomical receivers. The development of such a device will have a huge impact in mm & sub-mm astronomy & B-mode Cosmic Microwave Background (CMB) experiments, as a quantum-noise limited SPA with high gain before the mixer or the first stage detector will improve the receiver sensitivity by more than an order of magnitude.

In this project, the student will be studying the theoretical background and simulation technique to model the SPA, along with learning to use commercial electromagnetism software to design the amplifiers. The student will have the chance to get involve in the fabrication of the devices using state-of-the-art clean room facilities, either here in Oxford, or with our other collaborators. The student will also learn how to use sub-Kelvin cryogenics system and other experimental techniques, for measuring the performance of the amplifiers. In particular, the student will investigate the operation of the SPA at mm-wave frequencies, and their performance dependence on the physical temperature and the superconducting materials used to form the SPAs. Finally, the student will integrate the amplifier into an existing mm-wave astronomical receiver and assess the impact on the receiver performance.

This project falls within the astronomical instrumentation research area.