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

As society becomes increasingly data-driven, there is a need for computers that can keep up with the growing tide of information – as well as computers that can explore topics that traditional computers cannot tackle. , such as issues that cannot be reduced to “yes” or “no.”

With the ability to process large amounts of data at fast speeds as well as handle greater levels of ambiguity, quantum computers are seen as a solution. But quantum computers only work well when they have quantum bits — or “qubits” — short-lived individual particles that store information for processing. Longer-lived qubits will yield greater computing power.

Ph.D. student Joseph Soruco examines part of an ultrahigh vacuum chamber in Ruihua Cheng’s lab in the School of Science at IUPUI. Photo by Justin Casterline, Indiana University

The quest to “build a better qubit” is the focus of 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 member of the center, she and her students are working to understand a special class of molecules – called “cross-spin molecules” – that may have significant advantages over other Other candidates are currently being used as qubits.

Announced in 2021, the Quantum Technology Center is supported by NSF’s University-Industry Collaborative Research program, in which public and private institutions collaborate to advance the work of scientists study in many fields. According to Ricardo Decca, professor and chair of the Department of Physics in the School of Science at IUPUI, there are more than 80 such programs in the United States, but the Center for Quantum Technologies is the only one that focuses specifically on science and technology. quantum technology. , who helped lead the establishment of the center in Indiana.

Other members of the Quantum Technology Center include the Air Force Research Laboratory, Cummins Inc, Eli Lilly and Co., Hewlett Packard, IBM, Intel, Northrup Grumman and the Naval Surface Warfare Center-Can crane. Non-academic members sponsoring research projects under the program are granted early access to findings applicable to their institution.

Corporations are interested in quantum computers because of their potential to perform complex tasks not suited to traditional computers, Cheng said, including modeling complex systems like human cells; powering artificial intelligence; and protect personal data with encryption algorithms.

Ph.D. student Ashley Dale opens the ultrahigh vacuum chamber in the lab. Photo by Justin Casterline, Indiana University

For example, she said, a pharmaceutical company might want to quickly discover the effects of hundreds of thousands of chemical compounds on molecular pathways involved in a particular disease. Not only can quantum computers provide the computing power to rapidly simulate the effects of all these molecules in a cell, but they are also better equipped to handle the “gray areas” in simulations that The programmer cannot provide exact results for every molecule. Chemical interactions may occur.

A quantum computer is capable of modeling ambiguity because quantum bits can be understood as existing in multiple states simultaneously. Scientists can exploit this property to represent multiple outcomes at once, with different probabilities assigned to each state. The result is a computer that can quickly explore many potential outcomes.

In February, the Quantum Technology Center convened its first meeting with all participating partners to review project proposals. Cheng was part of two of the seven projects selected in the first round, both of which took advantage of her work on spin-switch molecules, supported under several NSF grants.

“Spin is one of the properties of electrons that can be manipulated or manipulated in different ways for the purposes of quantum computing,” she said. “Our work focuses on using voltages or electric fields to control spin in these molecules, which is a new approach that shows several potential advantages in quantum computing, including high Low power consumption and long combination time.

Coherence refers to the amount of time that cross molecules have useful spin as qubits.

“The longer the coherence time, the longer you can retain information for manipulation,” says Cheng.

This time is measured in 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 timing differences are significant despite their relatively short length is a testament to the power of these qubits compared to semiconductor-based qubits, she said.

Ultra-high vacuum chambers are used as part of experiments that use voltage or electric fields to control spin-switching molecules. Photo by Justin Casterline, Indiana University

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

Jared Phillips, Ph.D. student in Cheng’s lab, twice visited the Berkeley facility and collected data remotely. Based on the importance of his research, Phillips was honored with the best student research poster at the 68th International Symposium of the American Vacuum Society in November.

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

As a collaboration between academia and industry, Decca says the Quantum Technology Center is designed to not only facilitate this type of inter-institutional collaboration – a strength of academia – but also promote a private sector 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 team’s work.

“CQT also has a workforce development aspect,” said Decca, noting that students who participate in research projects funded through the center will graduate with technology skills high in accordance with the concerns of participating partners. “It is more likely that students will jump straight into these industries after graduation.”

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