Designing new materials as platforms for robust quantum devices

Thursday, May 25, 2023

For researchers to successfully engineer future quantum computers, it will be important for them to use the right materials.

Dr. Jonathan Baugh, a professor at the Institute for Quantum Computing (IQC) and the University of Waterloo’s Department of Chemistry, is working to create new, high-quality materials with desirable properties for these future applications in quantum computing.

After several years of work, Baugh and his collaborators have found a method for growing crystalline structures using the semiconductor indium antimonide, which has been engineered with specific purposes in mind. This is an exciting first step towards building designer quantum devices.

Baugh’s research group has created an indium antimonide platform designed for a type of qubit known as a Majorana fermion. While still theoretical, these qubits are predicted to have better resilience to noise and decoherence compared with other types of qubits due to their unique physics. Majorana qubits are shielded from outside influences due to the way their information is encoded across highly non-local quantum states. This protection is an attractive property that could make future quantum computers less susceptible to errors. Indium antimonide has a unique combination of properties, including high electron mobility and strong spin-orbit coupling, that when combined with a superconductor, yield just the right conditions for Majorana fermions to appear.

“Theoretically, indium antimonide has the best set of ideal ingredients that are needed for Majorana qubits, from a semiconductor point of view,” said E. Annelise Bergeron, the first author of the study and a PhD candidate at IQC and Waterloo’s Department of Physics and Astronomy. “Our research is the first to overcome some of the difficulties that previous research did not achieve in terms of a platform to build these devices for Majorana qubits.”

Their work was a true collaboration across the University of Waterloo community. Baugh and Bergeron worked with Professor Zbigniew Wasilewski’s Molecular Beam Epitaxy Group from the Waterloo Institute for Nanotechnology and the Department of Electrical and Computer Engineering at Waterloo, devices were fabricated in the Quantum-Nano Fabrication and Characterization Facility (QNFCF), and the team used specialized test facilities at the Transformative Quantum Technologies (TQT) program with IQC.

Wasilewski’s group grew wafer structures containing thin layers of indium antimonide called quantum wells, using a technique called molecular beam epitaxy. These quantum wells contain electrons confined to motion in a 2D plane, a configuration known as a 2D electron gas. Bergeron took these wafers and fabricated quantum devices known as gated Hall bars on the surface, which are used to measure the properties of the 2D electron gas. Bergeron and the team then characterized these devices using very low temperatures and strong magnetic fields – a regime in which the Hall resistance takes on quantized values, known as the quantum Hall effect regime. Their findings show that high quality 2D electron gases can be achieved in indium antimonide, with properties that are very promising for future Majorana qubit devices.

After many iterations of growing wafers, fabricating devices, and performing measurements, the team of collaborators has finally found a method that results in reproducible quantum well structures, reliable fabrication methods, and high-quality 2D electron gases.

“Indium antimonide has been plagued with difficulties in the past, which is why no one else has been successful with this material yet,” says Bergeron. “So, the fact that we reported on two wafer growths and multiple devices from each of those growths indicates that we’ve achieved a successful method of crystal growth and fabrication reproducibility. All of that together is quite the accomplishment!”

Now that the team has successfully overcome the hurdles for growing and characterizing these 2D electron gases in indium antimonide, they are excited to use this platform as a starting point for future work.

“We’re hoping that our research is setting the stage for a really unique new platform on which to build more interesting quantum devices and probe whether we can detect Majorana fermions,” said Baugh. “We’re at the dawn of working with this new material to see where we can take it.”

Field effect two-dimensional electron gases in modulation-doped InSb surface quantum wells was published in Applied Physics Letters on January 4th, 2023. This research was supported in part by the Canada First Research Excellence Fund through the TQT program at IQC.

Annelise Bergeron adjusting a piece of lab equipment

Learn more about this research on IQC's Quantum Today series

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