Producing superconductors for quantum circuit elements at high temperatures

A project led by the University of Melbourne’s Dr Manjith Bose and Professor Jeff McCallum, who are also members of the ARC Centre of Excellence for Quantum Computation and Communication Technology, has identified a promising class of superconductors that may potentially avoid the need for high levels of cryogenic cooling. These advanced materials can be manufactured, be integrable and compatible using standard silicon and superconducting electronics approaches. 

To optimise the growth of these silicide superconductors, Dr Bose and Prof McCallum are making extensive use of high-temperature neutron reflectometry on the Spatz reflectometer at ANSTO’s Australian Centre for Neutron Scattering. 

Neutrons are an ideal tool for exploring extreme sample environments, such as the high pressure, temperatures or fields that are present when manufacturing circuit elements. This is because neutrons can penetrate through most common metals, allowing one to see reflective thin films deep inside furnaces, magnets and cryo-chambers. 

"We were able to observe the growth rate on the nanometre-per-minute time scales at high temperatures of 800 °C," Dr Bose explained. Subsequently we were able to deploy cryogenic magnetometry measurements at ANSTO down to 3 K to detecting superconducting properties."

Some of the initial work was recently published in Applied Surface Science.  

The work was made possible by collaboration with ANSTO scientists Dr Anton Le Brun and Dr David Cortie, the team who previously achieved, as far as we know, the record for the highest temperature neutron reflectometry in 2024. Read more.  

Dr Le Brun commissioned and designed the Spatz reflectometer which transferred to ANSTO from Helmholtz Zentrum Berlin (HZB). Dr Cortie established a high temperature furnace capability on Spatz, working with the sample environment team at the Centre. He also performed the low temperature cryogenic measurements, which involved working at both extremes of the temperature scale. 

"Whilst ANSTO has dilution refrigerators that go to about 20 mK to enable work on quantum material, the great thing is we didn't even need them for this study," explained Dr Corti. "The material developed at Melbourne University operates about to about 16 K, so I was able to use a standard commercial cryo to measure the susceptibility which was much easier". 

The team also involved long-term neutron expert Emeritus Professor Trevor Finlayson, the recipient of the lifetime award of ANBUG Career Award in 2021. Read more. 

"Trevor kindly provided a wealth of advice, and he had worked on similar compounds in the 1960-1970s, albeit as bulk crystals rather than films. He provided original silicide samples from his PhD thesis in 1960, which were used as some of the calibration reference standards for our superconducting measurements," explained Dr David Cortie. 

"I think speaks highly of the resilience of this family of the silicide compounds. Using samples that were a half-century old also shows that true scientists never throw things away, even if our partners and family accusing us of being hoarders, because you just never know! " 

The joint Melbourne-ANSTO project to perfect the growth of the superconducting layers, is ongoing. The ANSTO group is also making the high temperature thin film capability, available to other university and industry groups facing similar challenges optimising thin films and surfaces. 

Quantum computers promise to revolutionise aspects of society by 2050. These tools are expected to influence every aspect in society, from how drugs are designed, your personal data security, through to how macroscale business logistics is implemented.   With 2025 being the UNESCO International Year of Quantum Science and Technology, there is a widespread recognition of untapped potential of quantum technology and computing to be unlocked in the coming century.

Amongst the different pathways, superconducting quantum computers have, so far, led to the largest available quantum processing units (QPUs) with 50-1000 qubits. Whilst encouraging, the drawbacks of these circuits is their noise, need for error-correction and a large amount of cooling power to operate at the necessary temperatures, typically below 1 Kelvin.

Thanks to Dr David Cortie and Dr Anton Le Brun for their assistance in preparing this content,