The University of Osaka develops "Zero-level distillation method" — Path to realizing fault-tolerant quantum computers

A research group led by Graduate Student Tomohiro Itogawa, Doctoral Students Yugo Takada and Yutaka Hirano, and Professor Keisuke Fujii from the Graduate School of Engineering Science at the University of Osaka has successfully developed a "zero-level magic state distillation method" for performing magic state distillation —essential for large-scale quantum computers—at low cost. Their research was published in Physical Review X Quantum.

To solve industrially important problems such as prime factorization and quantum chemistry calculations at high speed, fault-tolerant quantum computers with quantum error correction capabilities are essential. Fault-tolerant quantum computers need special quantum states called magic states.

However, creating magic states requires many resources. First, quantum information must be encoded with many qubits, and distillation protocols must be executed (logical-level magic state distillation). This method requires a large number of qubits and has a slow rate of magic state supply, necessitating dedicated "magic state factories" within quantum computers.

The research group dramatically reduced the computational cost required for magic state distillation by constructing error-resilient distillation circuits at the physical qubit level (zero level) rather than using logical qubits for distillation. As a result, the required number of qubits was reduced to approximately one-tenth and the required number of computational steps was halved compared with logical-level distillation.

The newly developed "zero-level magic state distillation" eliminates the need for magic state factories and dramatically reduces the number of qubits and computation time required for complex calculations, enabling the early realization of fault-tolerant quantum computers. Following the research group's presentation at academic conferences, Google's team also took notice. Google's team made further improvements and developed a technique called "magic state cultivation," demonstrating through its application that the number of physical qubits required for prime factorization could be reduced to one-tenth, thereby having a significant international impact.

Fujii commented: "This research began as Mr. Itogawa's undergraduate thesis theme when he was a fourth-year student. We started literally from zero, and initially I never imagined it would lead to results that solve such bottlenecks in fault-tolerant quantum computers. However, with support from his senior Mr. Takada, along with free thinking without preconceptions and creative ingenuity, it led to significant achievements."

Journal Information
Publication: Physical Review X Quantum
Title: Efficient Magic State Distillation by Zero-Level Distillation
https://journals.aps.org/prxquantum/abstract/10.1103/thxx-njr6