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Broadband Quantum-Limited Parametric Amplifier for Astronomy and Quantum Information Technology

Periodic Reporting for period 2 - SPA4AstroQIT (Broadband Quantum-Limited Parametric Amplifier for Astronomy and Quantum Information Technology)

Reporting period: 2020-08-01 to 2022-01-31

Amplifiers are generic components used in almost all electronic devices. They can be found in every type of radio, microwave, millimetre (mm), and sub-millimetre (sub-mm) wave instruments. However, even state-of-the-art High Electron Mobility Transistor (HEMT) amplifiers struggle to reach the quantum-limit noise level, and their substantial heat dissipation has limited their usage in many applications. Their performance deteriorates rapidly above 100GHz. A superconducting parametric amplifier (SPA), on the other hand, can achieve quantum-limited sensitivity over broad bandwidth. They are compact, easy to fabricate, dissipates negligible heat, and they can operate from radio up to THz frequencies. This project aims to develop the SPA technology to achieve ultra-broadband quantum limited amplifiers from microwave to mm/sub-mm wavelength.

SPA could play an important role in escalating the sensitivity of numerous astronomical instruments, and open up new research territories that have never been explored before. Their quantum-limited noise performance, low power requirement and negligible heat dissipation could improve system sensitivity significantly, and enable the construction of large astronomical array. This is important for satellite communication systems that have limited power and cooling capability. Their large bandwidth, high power handling and quantum-noise performance could have profound effect on quantum computing architecture as well, improve the fidelity to process hundreds of quantum bits (qubit) simultaneously. They can operate at THz frequencies, and in the era where electronic revolution is approaching mm-wave regime, development of mm-wave amplifier will have great potential for commercial applications too, such as beyond 6G systems to achieve several TB/s with link operating at 100-200 GHz, providing better quality and higher speed internet to end users. In the future, quantum computers will operate at higher frequencies to minimise the platform and increase computation power, which would certainly change the way end users engage with the new virtual platform. It is beneficial for biochemistry and pharmaceutical research too, where the wealth of chemistry lines in this region will allow probing of complex biology and chemistry behaviour in many systems, potentially finding new drugs and solution for medical issues such as cancer treatment.
The first half of the project focuses on preparing the ground works required to achieve the final scientific aims. Despite the difficulties arisen and progress being substantially delayed due to the global pandemic, we have managed to achieve several important milestones. We have commissioned a large and complicated cryogenic system that can achieve ultra-low physical temperature at 10mK. Along with this, we have also designed and constructed two other cryogenic systems, a 300mK and a 4K system, both designed and constructed in house. The experimental setup of both the 10mK and 300mK is partially completed for taking measurements, and upgrades will be underway throughout the project.

For this project, we aim to develop two different types of quantum amplifier: a kinetic inductance based (KI-) amplifier and a Josephson junction based (JJ-) amplifier. We have developed a unique theoretical framework that allow us to model the amplifiers with better accuracy, including losses and capability to optimise these designs. Using this framework, we have successfully designed and fabricated the first batch of the KI-amplifiers. This involves venturing into new techniques required and exploring new methodology before we finally successfully fabricated these novel devices. Once fabricated, we fabricated the dedicated sample holders to secure these devices. Intense characterisations are currently underway using the above-described cryogenic systems. We have since found several technical discrepancies, as well as the potential solutions to improve the performance. These findings have been reported in an academic paper, and presented in an international conference. Following this, we have prepared two new sets of KI-amplifiers, first to correct for these short-comings from the first batch including an optimised design, and second a novel KI-amplifier design that can achieve better performance with more compact design.

On the development of JJ-amplifiers, we have successfully improved the design performance of the conventional JJ-amplifier, achieving twice the bandwidth and 4 times less junctions required. This work has been reported in an academic journal and presented in an international conference as well. Along with this design, we have also come up with a novel solution to achieve JJ-amplifier with much high-power handling capability. Both designs are currently underway fabrication and test will commence soon.
The next stage of the project aims to continue characterise and improve the performance of the above-described microwave quantum amplifiers. This includes improving the design and perfecting the fabrication process, as well as tailored-made packaging to avoid unwanted interferences. We hope to conclude this work package by integrating the amplifier within an astronomical receiver and/or a qubit platform to test their feasibility of reading out these systems in comparison to conventional semiconductor amplifier.

As SPAs are fabricated using planar-circuit technology, they can be scaled easily from microwave to mm-wave frequencies, which is very difficult to achieve with the HEMT technology. Therefore, SPAs could be used as a first stage pre-amplifier of a mm-wave system to reduce the added noise of the overall system. This is because any loss introduced by the first component stage would be cascaded and compounded down the system chain, and increases the noise contributions of all the components along the chain. To the best of our knowledge, there is yet any demonstration of SPA operating beyond 40GHz, hence this work package, if successful, would be the first mm-wave SPA. We expect to develop a mm-SPA near 200GHz to demonstrate their feasibility as high frequency SPA, and compare their performance with conventional mixer-based operation.

SPA can also be configured to operate as a frequency converter. Within this context, we aim to develop a new type of mixer based on the SPA technology. Excitingly, unlike conventional frequency converters, SPAs not only down-convert the signal, it amplifies the converted signals as well. To the best of our knowledge, there is no evidence in the literature of attempts to operate the SPA in such mode yet. This is because of the limitation in retaining the broadband performance in the down-conversion process. We have since found several innovative solutions to the problem. As this work-package is challenging and is a new research area that has never been explored before, we expect to develop a microwave prototype operating near 20-40GHz to demonstrate the feasibility of operating a parametric mixer using the SPA technology, before venturing into the millimetre regime. The successful demonstration of developing a parametric mixer with high gain would have a significant effect on many fields, especially for large pixel count mm and sub-mm heterodyne receiver.
The 10mK dilution refrigerator commissioned.
Sample of a KITWPA from the first fabrication batch mounted in a dedicated sample holder.
The 300mK cryogenic system designed and built in-house.