Magically reducing errors in quantum computers

Osaka, Japan – For decades, quantum computers that perform calculations millions of times faster than conventional computers have remained a tantalizing yet distant goal. However, a new breakthrough in quantum physics may have just sped up the timeline.

In an article published in PRX Quantum, researchers from the Graduate School of Engineering Science and the Center for Quantum Information and Quantum Biology at The University of Osaka devised a method that can be used to prepare high-fidelity “magic states” for use in quantum computers with dramatically less overhead and unprecedented accuracy.

Quantum computers harness the fantastic properties of quantum mechanics such as entanglement and superposition to perform calculations much more efficiently than classical computers can. Such machines could catalyze innovations in fields as diverse as engineering, finance, and biotechnology. But before this can happen, there is a significant obstacle that must be overcome.

“Quantum systems have always been extremely susceptible to noise,” says lead researcher Tomohiro Itogawa. “Even the slightest perturbation in temperature or a single wayward photon from an external source can easily ruin a quantum computer setup, making it useless. Noise is absolutely the number one enemy of quantum computers.”

Thus, scientists have become very interested in building so-called fault-tolerant quantum computers, which are robust enough to continue computing accurately even when subject to noise. Magic state distillation, in which a single high-fidelity quantum state is prepared from many noisy ones, is a popular method for creating such systems. But there is a catch.

“The distillation of magic states is traditionally a very computationally expensive process because it requires many qubits,” explains Keisuke Fujii, senior author. “We wanted to explore if there was any way of expediting the preparation of the high-fidelity states necessary for quantum computation.”

Following this line of inquiry, the team was inspired to create a “level-zero” version of magic state distillation, in which a fault-tolerant circuit is developed at the physical qubit or “zeroth” level as opposed to higher, more abstract levels. In addition to requiring far fewer qubits, this new method led to a roughly several dozen times decrease in spatial and temporal overhead compared with that of the traditional version in numerical simulations.

Itogawa and Fujii are optimistic that the era of quantum computing is not as far off as we imagine. Whether one calls it magic or physics, this technique certainly marks an important step toward the development of larger-scale quantum computers that can withstand noise.

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The article, “Efficient Magic State Distillation by Zero-Level Distillation,” was published in PRX Quantum at DOI: https://doi.org/10.1103/thxx-njr6.

About The University of Osaka

The University of Osaka was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.

Website: https://resou.osaka-u.ac.jp/en