Superconducting Qubit Research at the SQuID Lab

Superconducting quantum computing devices are some of the most promising candidates for building large-scale quantum computing systems, and a rich resource for quantum information science research. The Superconducting Quantum Information Devices Lab (SQuID Lab) research group at the Niels Bohr Institute, University of Copenhagen studies exactly these devices and systems as part of the Novo Nordisk Foundation Quantum Computing Programme (NQCP).

We talked with the lab’s principal investigator, Morten Kjaergaard, Associate Professor of Quantum Information Physics at the Niels Bohr Institute, about the research group’s work and their new lab. The new lab has two XLDsl dilution refrigerators, which were the first systems Bluefors delivered utilizing our new Gas Handling System Generation 2.

Read on to find out about their research, their experience of setting up this new lab, and how these new systems serve their research. You can also watch Morten’s interview and see the impressive lab in action.

Research into Superconducting Quantum Computing Systems

Morten Kjaergaard heads the superconducting qubit team at the NQCP, with the SQuID Lab being a research team operating jointly at NQCP and the Center for Quantum Devices at Niels Bohr Institute. Their work primarily focuses on superconducting quantum computing systems, a field that has seen a dramatic increase in interest over the past decade. The Niels Bohr Institute, renowned for its contributions to physics research, provides an ideal environment for research in this domain.

Morten and his team are conducting research in two main areas: developing new types of qubits, and understanding the fundamental nature of quantum information. The lab’s work on superconducting qubits involves exploring innovative materials and designs to build better, more efficient qubits, working towards realizing fault-tolerant quantum computing systems. This work involves a combination of theoretical and experimental approaches, leveraging the fabrication, testing, and cryogenic equipment available at the institute.

One of key aspects of the research is the quantum characterization of qubits and their operation. The team aims to determine new methods for evaluating the quality and performance of qubits, which is crucial for the development of reliable quantum computing systems.

“There are many ways to characterize qubits, and many of them are very well established. But there are still fundamental questions about what is the right way to characterize the “quality of qubits”. A lot of our work here at NQCP, and the Center for Quantum Devices, is focused on these kinds of questions,” Morten explains.

At the same time, the lab explores fundamental questions about quantum information, such as what makes quantum computers special, and the implications of information becoming quantum. This research is not just about the practical applications of quantum computing but also about understanding the fundamental aspects and the unique properties of quantum information.

Collaborative Research

The team also collaborates with other research groups on superconducting qubit development. After completing his PhD studies, Morten undertook postdoctoral research at MIT under the guidance of Professor Will Oliver. This experience was pivotal in shaping his focus on superconducting qubit systems; expertise which he later brought back to Copenhagen to establish his own lab. Now his team collaborates with the Engineering Quantum Systems group at MIT as part of the NQCP. This partnership involves establishing parallel labs at both institutions, using the same technological backbone to complement their work. This setup allows for seamless collaboration, with students and researchers frequently exchanging ideas and working together on joint projects.

On the benefits of collaboration, Morten comments: “We can co-develop all aspects of realizing advanced multi-qubit systems, and make everything modular across multiple sides, and thereby really work together. And especially in the beginning, we are learning a lot from the MIT side as we’re building up capabilities here. This means that we can send students back and forth.”

Modern superconducting quantum information systems are based on years of accumulative research by the community. This technological development has led to ever-larger multi-qubit systems with improving fidelities, complemented by advances in the surrounding measurement infrastructure.

“For us to be able to partner with a team such as the one at MIT is a great way for us to tap into one of the world’s leading teams and collaborate with them. Then, here on our side, we are specifically focused on very sophisticated software development for very fast, very large-scale multi-qubit control that enables us to explore the exciting interface between advanced qubit control and quantum benchmarking. And now we’re starting to see the first results of those two directions coming together,” he said.

Setting Up the New Lab

2024 was a year of foundation-building for the SQuID Lab. Setting up the lab was a significant undertaking, and the team’s experience was both challenging and rewarding. Over the course of a year, the team transformed an empty room into a fully functional lab equipped with two Bluefors XLDsl dilution refrigerators, lots of control hardware, and various other equipment. Of the two dilution refrigerators, the XLD400sl is supported by the Innovation Fund Denmark with the XLD1000sl part of the NQCP.

Setting up the lab involved meticulous planning and coordination to ensure that every detail was considered. A dedicated team of PhD students and senior researchers worked hard to design and set up the lab, paying close attention to each piece of equipment.

“Building up a sophisticated modern superconducting qubit lab is not something one person can do. It’s a big team effort. And in this case, our team consisted of half of the entire research lab focused on this effort. We had 4 PhD students and a couple of senior researchers working almost full time, thinking through every single cable, every single connection,” Morten says.

Great care was taken to design the layout of the lab and its equipment, even down to the specific design of the tables to match rest of the room. The environment was not only designed to be a great home for the cryostats, but also the researchers working in the room, with noise isolating doors, acoustic panels, and many other details such as functional and ergonomic Scandinavian furniture making the lab a pleasure to work in.

The team’s hard work and dedication have resulted in a state-of-the-art facility, ready to research multi-qubit systems and fundamental questions in quantum information science.

Next Generation Bluefors Systems

The heart of the lab is the two XLDsl dilution refrigerators, both powered by the new Generation 2 Gas Handling Systems. Installed at the lab in April with the help of Bluefors Cryo Engineers, the reliability and stability of the Bluefors systems has been instrumental for their research.

“They reached less than ten millikelvin right off the bat, even with a lot of components inside. We’re very happy with that. The systems are incredibly stable – and with high fidelity superconducting quantum information systems, reliability is really the name of the game,” Morten says about systems.

Noting the benefits of the Gas Handling System Generation 2, Morten says: “The new Gas Handling Systems have been incredible to work with. In fact, they have almost been too good, in the sense that we haven’t really had a chance to test them because they have always done what we asked. That is of course a good thing. It means they’re highly reliable, but they’re also very good for interfacing with, with the new touchscreen interface.”

The intuitive Control Software has proven to be a significant asset, allowing the team to quickly assess the status of their experiments.

“The new control software doesn’t just have cool animations. It’s also very intuitive to work with. In particular, it’s very easy to customize views of what you would like to plot against each other. All that might seem like a small thing, but it’s actually hugely helpful for very quickly getting a sense of what the status of the fridge is,” he explains. “We have a number of our own custom views already, helping us to see what we really care about.”

Ready to Explore Quantum Information

After ten months of hard work, the SQuID Lab is filled with cold dilution refrigerators, many qubits, lots of control hardware, and a team of happy and excited students and researchers. With the lab now fully operational, Morten and his team are starting to carry out experiments with their new systems, ready to explore the many facets of quantum information.

“I’m very excited for the students who have now spent a long time building up this incredible lab space to get into the nitty gritty of controlling qubits – many qubits – and really understanding the multi-faceted nature of what it means to operate and orchestrate multi-qubit systems,” Morten concludes.

Find out more about Bluefors XLD systems and the next generation Gas Handling System powering them.