Scaling Quantum: how Cryo-CMOS blueprints bridge the gap to scalable quantum computers

Leaders from industries all over the world are discussing the transformative benefits that quantum computers could deliver. There are multiple candidates for scalable quantum computing platforms, based on different qubit (“quantum bit”) modalities. Solid state devices such as superconducting and spin qubits are attractive due to their overlap with well-understood and well-controlled semiconductor fabrication processes. 

However, in constructing a quantum computer using ultra-low temperature solid-state qubits, it is not only the qubits that need to operate in such incredibly low temperature environments, but control and interface components also need to work in this regime.

The electronic control that we use in classical computing today operates at room temperature, in stark comparison to the extremely cold cryogenic environment of a quantum processor. Most quantum computing controllers currently sit outside that cryogenic environment. The aim of many university and industry researchers is to bring this control closer to the processor to increase speed and reduce electronic noise.

Enter: Cryo-CMOS, or Cryogenic Complementary Metal-Oxide-Semiconductors.

Ray Spits, Collaboration Programmes Manager at Oxford Instruments NanoScience
Paul Wells, CEO at sureCore
Martin Weides, Professor of Quantum Technologies at University of Glasgow

The Cryo-CMOS solution

CMOS process technology has been the bedrock of the semiconductor industry for over 30 years. It has enabled the transformative power of Moore’s Law to revolutionise the modern world. CMOS typically operates between -40 °C and 125 °C which covers the vast majority of electronic products sold on the market today. By measuring and understanding how CMOS performance changes when temperatures are reduced into the cryogenic realm, a whole new design capability was discovered. In doing so the term ‘Cryo-CMOS’ was coined to characterise these specialist electronic circuits that can be designed to work at very low temperatures. 

Not only can Cryo-CMOS circuits survive the cold, but they also reduce the complex and bulky cabling currently used to connect quantum computer components. This is a way that we may be able to scale quantum computers more effectively.

One programme helping to facilitate the development of these essential components is an Innovate UK-funded consortium, led by sureCore with the support of Oxford Instruments NanoScience and the University of Glasgow among others. 

Can you explain the Cryo-CMOS project? What is its goal? 

To develop modern chips, designers need access to a range of key predesigned functions. These include logic gates, flip-flops and memories – the essential building blocks of any digital chip - as well as more specialist blocks.

Such blocks are only available for the standard operating temperature ranges. To be useful in the cryogenic quantum space, Cryo-CMOS is needed so that control chips can be designed for these harsh environments.

To help address this, the Innovate UK project developed the low-level transistor simulation models needed to create the key building blocks. The project then created a range of cryogenic building blocks that will now facilitate the design of advanced cryogenic control chips, addressing a critical challenge in quantum computing: efficient qubit and system scaling.

The project kicked off in early 2021 and has run for 36 months, during which our primary goal was to develop cryogenic transistor simulation models (so called SPICE models) for silicon-based CMOS circuits that can operate at ultra-low temperatures. These models were then used to develop a range of key building blocks, essentially a comprehensive “toolbox” for semiconductor chip designers to help enable them to design integrated circuits.

The transistor models and the building blocks we have created will enable the design of control chips capable of qubit manipulation, data readout, and efficient data storage and processing at extremely low temperatures. This will in turn accelerate quantum computing development by making designing electronics for the cryogenic space easier and eliminating the need for extensive cabling.

What is Oxford Instruments’ role? 

One of the most critical challenges in this endeavour is managing heat generation. The obvious solution is to co-locate the control electronics with the qubits in the cryostat but this requires both to be kept at ultra-low temperatures. Not only is space limited in the cryostat, but the modern semiconductors that make up these chips only work down to -40° C.

We helped overcome this challenge by providing one of our specialised 3 K (-270 °C) cryostats with a custom temperature-controlled measurement plate, enabling precise transistor characterization between 3 and 200 K. We adapted this cryostat by implementing a custom designed stage that allowed the temperature-controlled evaluation of mounted test cryo-CMOS devices.

We offer the environments needed to understand and model why the operating characteristics of the electronics change when the temperature is reduced to absolute zero. From here, our partners in the project will be able to design a portfolio of cryo-CMOS IP, enabling the creation of custom chips that can interface to the qubits at cryogenic temperatures and support controller functionality.

Who else is involved in the project?

The project brings together a strong consortium of quantum research and industry leaders, led by sureCore, with the University of Glasgow, Synopsys, Universal Quantum, SEEQC, and Semiwise. This collaborative approach ensures a holistic solution to the quantum computing challenges. The more we collaborate, the faster we can implement quantum computing in real-world applications for life-changing projects, and head closer towards quantum’s commercialisation.

We have strong ties with several of the organisations involved. SureCore, a low power semiconductor design specialist, is leading this project. Paul Wells, CEO at sureCore comments:

“This is an extremely exciting project. Quantum computing has the potential to make a huge impact across the globe. Our goal is to accelerate quantum computing scaling by enabling the migration of the control electronics into the cryostat to be closer to the qubits. All the consortium members have made invaluable contributions, and we are really proud of the impressive results seen so far. We are now able to offer to the market, for the first time, a range of Cryo-CMOS semiconductor IP”

We are especially close to the University of Glasgow and Prof. Martin Weides' group with whom we have collaborated on a number of Innovate UK projects. One of these was a project exploring 'Reliable, high throughput production and characterisation of coherent superconducting devices', otherwise known as FABU, alongside Oxford Quantum Circuits:

“The collaboration with Oxford Instruments NanoScience has been pivotal in advancing our research in quantum technologies” said Martin Weides, Professor of Quantum Technologies at the University of Glasgow. “The custom-made 3 K cryostat, equipped with a variable temperature stage, has become a cornerstone of our experimental setup. Its large volume and robust cooling power enable the simultaneous integration and testing of multiple devices under cryogenic conditions, significantly enhancing our research efficiency.”

“Furthermore, this cryostat allows us to reliably and swiftly pre-test a wide range of devices, ranging from simple transistors to off-the-shelf and our bespoke application-specific integrated circuits (ASICs), from DC up to microwave frequencies. It serves as a critical enabler for the success of this Innovate UK-funded Cryo-CMOS project, streamlining the development of cryogenic control and readout electronics for scalable quantum computing technologies. Moreover, its unique capabilities play a vital role in bridging the gap between research outcomes and commercial applications, particularly through Kelvin Quantum, our startup focused on cryogenic electronics.”

What are the next steps? What will happen now that the project is coming to a close? 

SeeQC and Universal Quantum will now evaluate the Cryo-CMOS devices, potentially paving the way for commercial products. The developed intellectual property will be made available to quantum computing startups.

This collaborative effort represents a significant step towards making quantum computing more accessible, efficient, and scalable. By addressing the fundamental challenges of quantum system design, the consortium is bringing us closer to revealing the transformative potential of quantum technologies, promising a future where complex computational problems can be solved with unprecedented speed and efficiency.