Researchers from The University of Osaka invent a technique to dramatically decrease overhead of 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.