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Improving quantum computing through quest to ‘build a better qubit’

IUPUI physicist’s research is part of project supported by Center for Quantum Technologies

Aug 1, 2023

As society becomes increasingly data driven, there’s a growing need for computers that can keep pace with the swelling tide of information — as well as computers that can explore topics that aren’t answerable with traditional computers, such as problems that can’t be reduced to “yes” or “no.”

With their ability to process large amounts of data at rapid speeds, as well as handle greater levels of ambiguity, quantum computers are seen as a solution. But a quantum computer is only as good as its quantum bits —or “qubits” — the individual, short-lived particles that store information for processing. A qubit that lasts longer provides greater computational capacity.

A man in a blue flannel shirt and lab gloves examines a stainless steel piece of laboratory equipment Ph.D. student Joseph Soruco examines part of the ultra-high vacuum chamber in the lab of Ruihua Cheng at the School of Science at IUPUI. Photo by Justin Casterline, Indiana University

This quest to “build a better qubit” is central to the research of Ruihua Cheng, an associate professor in the Department of Physics in the School of Science at IUPUI. Her work is supported by the Center for Quantum Technologies, a National Science Foundation-supported collaboration between IU, Purdue and Notre Dame. As a part of the center, she and her students are working to understand a special type of molecule — known as a “spin crossover molecule” — that could hold significant advantages over other candidates currently used as qubits.

Announced in 2021, the Center for Quantum Technologies is supported by the NSF’s Industry-University Cooperative Research program, in which public and private organizations cooperate to advance the work of scientists in a wide range of areas. There are over 80 of these programs in the United States, but the Center for Quantum Technologies is the only center specifically focused on quantum science and technology, according to Ricardo Decca, professor and chair of the Department of Physics at the School of Science at IUPUI, who helped lead the center’s establishment in Indiana.

Other members of the Center for Quantum Technologies include the Air Force Research Laboratory, Cummins Inc, Eli Lilly and Co., Hewlett Packard, IBM, Intel, Northrup Grumman and Naval Surface Warfare Center-Crane. Non-academic members who sponsor research projects under the program are granted early access to findings applicable to their organizations.

Corporations are interested in quantum computers due to their potential for complex tasks that aren’t suited to traditional computers, Cheng said, including modeling complex systems such as human cells; powering artificial intelligence; and protecting personal data with cryptographic algorithms.

A woman smiles as she watches a large metal disc lift from the top of a stainless steel piece of physics lab equipment Ph.D. student Ashley Dale opens the ultra-high vacuum chamber in the lab. Photo by Justin Casterline, Indiana University

For example, she said, a pharmaceutical company might want to rapidly explore the effect of hundreds of thousands of chemical compounds on a molecular pathway related to a specific disease. A quantum computer could not only provide the computational power to quickly simulate the effect of all of these molecules in a cell, but also be better equipped to handle “gray areas” in the simulation where a programmer can’t provide the exact result of every possible chemical interaction.

A quantum computer has the ability to model ambiguity because quantum bits can be understood to exist in multiple states simultaneously. Scientists can exploit this property to represent more than one outcome at the same time, with different probabilities assigned to each state. The result is a computer that can quickly explore a wide range of potential outcomes.

In February, the Center for Quantum Technologies convened its first meeting of all participating partners to review project proposals. Cheng is a part of two of the seven selected first-round projects, with both leveraging her work on spin crossover molecules, supported under several NSF grants.

“Spin is one of the properties of an electron that can be controlled or manipulated in different ways for the purposes of quantum computing,” she said. “Our work focuses on using electric voltage or electric fields to manipulate the spin in these molecules, which is a novel approach that suggests several potential advantages in quantum computing, including low power consumption and long coherence time.”

Coherence refers to the amount of time spin crossover molecules are useful as qubits.

“The longer the coherence time, the longer you can preserve information for manipulation,” Cheng said.

These times are on the scale of microseconds, milliseconds or longer, she added. That’s 100 to 1,000 times longer than some other materials currently used as qubits. The fact that these time differences are significant despite their relatively short length is a testament to these qubits’ power compared to semiconductor-based qubits, she said.

A device comprised of stainless steel cylinders, gauges, sensors and vacuum pumps on a lab bench The ultra-high vacuum chamber is used as part of experiments that use electric voltages or electric fields to manipulate spin-crossover molecules. Photo by Justin Casterline, Indiana University

To run their experiments, Cheng’s lab uses spin crossover molecules produced at the Lawrence Berkeley National Laboratory in California, which are synthesized in powder form for safe transport. To manipulate and study the spin in the molecules, Cheng’s students use a variety of highly specialized machines, including equipment at IUPUI’s Integrated Nanosystems Development Institute. She also sends students to Berkeley to conduct experiments on site.

Jared Phillips, a Ph.D. student in Cheng’s lab, has twice traveled to the facility at Berkeley, as well as collected data remotely. Based on the significance of his research, Phillips was honored for the best students’ research poster at the American Vacuum Society 68th International Symposium in November.

As a part of the Center for Quantum Technologies, Cheng’s research does not occur in isolation; she is working with other center colleagues to gain a more comprehensive understanding of these molecules. Collaborating researchers include Jing Liu at the School of Science at IUPUI, who will study the optical properties of the molecules’ behavior, and Babak Anasori at the School of Engineering and Technology at IUPUI, who provides special 2D materials used as a foundation for the molecules. IU Bloomington, Purdue and Notre Dame researchers are also a part of the projects.

As a collaboration across academia and industry, Decca said the Center for Quantum Technologies is designed to not only facilitate this type of cross-institutional collaboration — a strength of academia — but also leverage the private sector’s focus on rapid innovation. Each month the lead researcher on each project meets with the center’s industry partners to incorporate their feedback into the teams’ work.

“There’s also a workforce development aspect to the CQT,” Decca said, noting that students who participate in research projects funded through the center graduate with high-tech skills tailored to the interest of the participating partners. “There’s high potential for students to jump straight into these industries upon graduation.”

In addition to monthly meetings, a full meeting of the center’s partners occurs twice a year. The next of these meetings, which are open to the public, will take place on the IUPUI campus in October.

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