Quantum computing is considered the next generation of information technology, with the potential to revolutionize an array of fields, including machine learning, drug development, data storage, agriculture and cybersecurity.

Using the principles of quantum mechanics will allow researchers to quickly solve complex problems that are currently insurmountable by classical computers. 

However, adoption of quantum technologies has been stymied by several factors, including high error rates. These mistakes occur because quantum systems are highly sensitive to external disturbances like temperature and sound. Effective error correction would protect high-performance data processing, but this area of research has had limited exploration, until now.

University of Arizona College of Engineering researchers Christos Gagatsos and Bane Vasic received two grants from the federal government to advance novel areas in quantum information. Gagatsos was awarded $1.4 million from the U.S. Army Research Office to investigate the application of quantum error correction in magnetic field sensing, and Vasic was awarded $600,000 from the National Science Foundation to stabilize quantum computing with error correction codes.

"The most exciting aspect of this work is that we are simultaneously developing new technology and advancing fundamental science," said Gagatsos, an assistant professor of electrical and computer engineering and optical sciences.

Quantum sensing may revolutionize magnetometry

Gagatsos is using error correction to improve the measurement capability of quantum magnetic field sensors, which could impact a host of fields.

"Several potential applications come to mind," he said, "including navigation and geolocation, and medical imaging, which involves measuring magnetic fields produced by neural activity in the brain." 

Leading a multidisciplinary team in this relatively uncharted area of research, Gagatsos is joined by electrical and computer engineering assistant professor Narayanan Rengaswamy.

"As someone trained to perform error correction in communications, data storage and quantum computing, the goals and challenges in quantum sensing are unique," Rengaswamy said.

One of the project's researchers, Xiaodong Yan, an assistant professor of materials science and engineering and electrical and computer engineering, will conduct physical experiments on the team's designs. 

Yan said they aim to build quantum sensors, which will be placed inside a probe, to verify theoretical findings. The team will develop the device inside two on-campus cleanrooms and test beds.

In a break from typical methodology, the researchers intend to use a Bayesian approach, rather than Fisherian, when building the sensors. This means that their devices will incorporate prior information into the model instead of relying solely on the received data. According to Gagatsos, this shift in strategy will augment data processing.

Coding a quantum computer

With $600,000 from the NSF's Division of Computing and Communication Foundations, Vasic, a professor of electrical and computer engineering and mathematics – along with Nithin Raveendran, an assistant professor of electrical and computer engineering, and additional collaborators – will delve into quantum low-density parity-check, or QLDPC, codes. These error correction codes harness principles of quantum physics to stabilize quantum computers as they conduct tasks.

"There is no system now that uses these QLDPC codes," he said. "It will enable large-scale quantum computing."

QLDPC codes control how qubits – microscopic units of information – transmit their data in quantum computers to solve problems. These codes solve problems with fewer qubits than the more popular method of topological codes, while also protecting them from errors.

Qubits need to be stabilized to conduct large-scale computing, but these bits can be easily destroyed. For example, qubits must be stored in a refrigerator at temperatures nearing absolute zero to protect them from the environment. 

Vasic, also the director of the university's Error Correction Laboratory, explained that another way to stabilize these qubits is with entanglement. This fundamental phenomenon of quantum physics occurs when two particles – in this case qubits – become so deeply connected that they mimic state changes across distances.

"What technology in the past allowed is that only nearby qubits are entangled," he said. "But now, new technology allows entanglement of qubits that are farther away, that are not local."

QLDPC codes show promise in entangling qubits at farther distances to conduct tasks, saving time, money and power resources. Without these quantum error correction codes, the qubits at a distance would start in a quantum state, or entanglement, and just disappear.

"Imagine a new internet, a new computer connected to internet and how much faster it will be. You can solve problems that would take thousands of years on a classic computer to solve."