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A Mathematical Shortcut for Determining Quantum Information Lifetimes

Scientists have uncovered a mathematical shortcut for calculating an all-important feature of quantum devices.

Having crunched the numbers on the quantum properties of 12,000 elements and compounds, researchers have published a new equation for approximating the length of time materials can maintain quantum information, called 'coherence time.'

The formula allows scientists to estimate materials' coherence time almost immediately - versus the hours or weeks it would take to calculate an exact value.

"People have had to rely on complicated codes and calculations to predict spin qubit coherence times. But now people can compute the prediction instantaneously. This opens opportunities for researchers to find the next generation of qubit materials," said Shun Kanai, professor at the Research Institute of Electrical Communication at Tohoku University, and lead author of the study.

The team, which comprised Kanai, current Tohoku University president Hideo Ohno, and researchers from Argonne National Laboratory, the University of Chicago, and Ajou University, published their results in April in the Proceedings of the National Academy of Sciences.

The team's equation applies to a particular class of materials - those that can be used in devices called spin qubits.

Qubits are a fundamental unit of quantum information: the quantum version of classical computer bits. They come in different forms and varieties, including a type called the spin qubit. A spin qubit stores data in a material's spin - a quantum property inherent in all atomic and subatomic matter, such as electrons, atoms, and groups of atoms.

Scientists expect that quantum technologies will improve our everyday lives. We may be able to send information over quantum communication networks that are impenetrable to hackers, or we could use quantum simulations to speed up drug delivery.

The realization of this depends on having qubits that are stable enough - i.e., have long enough coherence times - to store, process, and send the information.

While the research team's equation only predicts a material's coherence time, it gets close to the true value. And what the equation lacks in precision, it makes up for in convenience. It requires only five numbers - the values of five particular properties of the material in question - to get a solution.

Diamond and silicon carbide are currently the best-established materials for hosting spin qubits. Now scientists can explore other candidates without having to spend days calculating whether a material is worth investigating further.

Figure 1 indicates the widegap materials estimated to have longer coherence time over 1 ms. Sufficiently long coherence time has been obtained for more than 800 materials. Most of them are the under-explored chalcogenides.

Types of 832 stable widegap compounds with predicted quantum coherence time longer than 1 ms. S. Kanai et al.

"The equation is like a lens. It tells you, 'Look here, look at this material. It looks promising,'" said University of Chicago professor and Argonne senior scientist Giulia Galli, co-author of the study and collaborator at Q-NEXT, a DOE National Quantum Information Science Research Center led by Argonne National Laboratory. "We are exploring new qubit platforms and new materials. Identifying mathematical relationships like this one leads us to new materials to combine."

With this equation in hand, the researchers plan to boost the accuracy of their model.

They will also connect with researchers who can create the materials with the most promising coherence times, testing whether they perform as well as the equation predicts. The team has already marked one success. A scientist outside the team reported that the relatively long coherence time of a material called calcium tungstate performed according to the team's formula.

"Our results help us with advancing current quantum information technology, but that's not all," said Ohno. "It will unlock new possibilities by bridging the quantum technology with a variety of conventional systems, allowing us to make even greater progress with the materials we're already familiar with.

Publication Details:

Title: Generalized scaling of spin qubit coherence in over 12,000 host materials
Authors: Shun Kanai, F. Joseph Heremans, Hosung Seo, Gary Wolfowicz, Christopher P. Andersong, Sean E. Sullivan, Mykyta Onizhuk, Giulia Galli, David D. Awschalom, and Hideo Ohno
Journal: Proceedings of National Academy of Science
DOI: 10.1073/pnas.2121808119

Press release in Japanese


Shun Kanai
Research Institute of Electrical Communication

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