Over the last three decades, quantum computing has advanced from a mere theoretical fable to a global business. It is moving closer to the possibility of a technology that will someday solve problems that are too complicated for some of the strongest supercomputers. MIT Lincoln Laboratory is not just in the forefront of research. However, it is also offering quantum research to the broader community via it is Superconducting Qubits located at the Lincoln Laboratory (SQUILL) Foundry.
Quantum bits (qubits) are the essential building of the quantum computer’s blocks similar to transistors in conventional computers. There are numerous ways of making a qubit. One of the most exciting is superconducting qubits. These are produced by utilizing circuits that are made of superconducting components. They are made with the same techniques as conventional microelectronics, for example, depositing and cutting thin metal films onto the substrate. They are then operated in near-zero temperatures to create “artificial atoms.”
Quantum computing will require fundamental research and experimentation with the qubits and other qubits. Superconducting qubits are challenging, and the biggest obstacle for scientists who wish to explore this field is the high cost of tooling and the specialized processes required to create the circuits.
It was in the SQUILL Foundry was constructed to eliminate this obstacle. The Laboratory sponsors the Foundry for Physical Sciences (LPS) Qubit Collaboratory, a National Quantum Initiative-funded center. The program provides Lincoln Laboratory’s leading-edge manufacturing facilities accessible for free to organizations working on U.S. research funded by the government. Researchers cancan submit quantum circuits for fabrication, and the completed circuits can be used to enhance research in their facilities.
“Democratizing access to robust, reliable qubit fabrication dramatically lowers the barrier to entry in superconducting qubits,” says Mollie Schwartz, the principal researcher of the project and the leader of Superconducting Qubit Research in the Lincoln Laboratory. “We want to enable researchers whose core focus is not in materials and fabrication to really focus on driving progress in the areas of superconducting qubit research that they are most interested in, and to allow the community to leverage some of the more advanced capabilities we’ve developed.”
One Foundry user, Stanford University Professor David Schuster, says that the SQUILL Foundry has enabled researchers in the lab’s quantum field to think about experiments that they would previously not have tried because of the difficulty of the nanofabrication process. “It has allowed my younger students to design and measure complex quantum circuits much faster than they could in the past,” Schuster says.
A super-specialized area
One of the main benefits of superconducting qubits is their flexibility in design: Their behavior and dynamics are not controlled by nature, as the physical atom. Instead, they can be designed by combining inductors, capacitors, and Josephson junctions (a kind of superconducting switches) in innovative ways to generate the energy landscape of your choice; because of this, superconducting qubits are an array of quantum circuits, which are different in appearance and function in distinctive ways.
Achieving the highest level of technology in superconducting qubit hardware requires expertise across various disciplines, including fabrication, materials, the design, and simulation of circuits packaging, cryogenics, and packaging low-noise measurement, interfacing between hardware and software, and quantum compiling. As the understanding of processes and materials has grown, the fabrication of top-quality qubits has become increasingly dependent on millions of dollars worth of fabrication equipment and countless hours of development and sustainability.
“It has become increasingly challenging for individual organizations to maintain this full stack of expertise, particularly as circuits become more complex to design, fabricate, and measure,” Schwartz states. “As a result, superconducting qubit hardware research has remained centralized into a relatively small number of laboratories and large universities capable of developing and sustaining this expertise.”
MIT Lincoln Laboratory is one of these labs, boasting over 20 years development and research in superconducting qubits and demonstrations of the world’s best qubit performance. Qubits are developed on-site within the Microelectronics Laboratory, thought to be among the U.S. government’s most advanced foundries, and in highly specialized prototyping facilities. The expertise and equipment of this lab has allowed them to set up in the SQUILL Foundry.
From qubit design to delivery
The SQUILL Foundry was first used as a pilot program from July 2021 until February 2023. It was open to a select group of users with diverse experience within the industry, ranging from established leaders to fresh faculty, including institutions with sophisticated fabrication facilities and those with little or no fabrication facilities.
The participants received a design rule guide and examples of physical layout files that can serve as an initial basis for developing their ideas. Additionally, they received a top-quality “candle qubit” chip that allows users to test their quantum measurement devices at home. “It’s a chip that we’ve already done measurements on, and then they can measure the same chip in their systems to make sure that those systems are meeting expectations,” says Cyrus Hirjibehedin, who led the user interaction for the project. “Overall, the process has gone very well, and we’ve received overwhelmingly positive feedback from our users.”