Researchers one step closer to practical quantum computing

Fujitsu and Osaka University’s Center for Quantum Information and Quantum Biology (QIQB) have developed a highly efficient analog rotation quantum computing architecture, in a step towards realising the potential of practical quantum computing. The new architecture reduces the number of physical qubits required for quantum error correction — a prerequisite for the realisation of fault-tolerant quantum computing (FTQC) — by 90% from 1 million to 10,000 qubits. This will allow research to commence on the construction of a quantum computer with 10,000 physical qubits and 64 logistical qubits, which corresponds to computing performance of approximately 100,000 times that of the peak performance of conventional high performance computers.

Fujitsu and Osaka University will further refine this new architecture to lead the development of quantum computers in the early FTQC era, with the aim of applying quantum computing applications to a range of practical societal issues including material development and finance.

Gate-based quantum computers are forecast to revolutionise research in a range of fields including quantum chemistry and complex financial systems, as they will offer higher calculation performance than current classical computers. Logical qubits, which consist of multiple physical qubits, play a key role in quantum error correction technology and ultimately the realisation of practical quantum computers that can provide fault-tolerant results.

Within conventional quantum computing architectures, calculations are performed using a combination of four error-corrected universal quantum gates (CNOT, H, S and T gate). Within these architectures, quantum error correction for T-gates especially requires a large number of physical qubits, and rotation of the state vector in the quantum calculation requires repeated logical T-gate operations for approximately 50 times on average. Thus, the realisation of a genuine fault-tolerant quantum computer is estimated to require more than one million physical qubits in total.

For this reason, quantum computers in the early FTQC era using conventional architecture for quantum error correction can only conduct calculations on a limited scale, below that of classical computers, as they work with a maximum of about 10,000 physical qubits, a number far below that required for genuine, fault-tolerant quantum computing. To address these issues, the researchers developed an analog rotation quantum computing architecture that is able to reduce the number of physical qubits required for quantum error correction, and enable quantum computers with 10,000 physical qubits to perform better than current classical computers, accelerating progress toward the realisation of genuine, fault-tolerant quantum computing.

By redefining the universal quantum gate set, Fujitsu and Osaka University succeeded in implementing a phase rotating gate which enables highly efficient phase rotation, a process which previously required a high number of physical qubits and quantum gate operations. In contrast to conventional architectures that required repeated logical T-gate operations using a large number of physical qubits, gate operation within the new architecture is performed by phase rotating directly to any specified angle.

In this way, the researchers succeeded in reducing the number of qubits required for quantum error correction to around 10% of existing technologies, and the number of gate operations required for arbitrary rotation to approximately 5% of conventional architectures. Fujitsu and Osaka University also suppressed quantum error probability in physical qubits to about 13%, thus achieving highly accurate calculations.

Image credit: iStock.com/Bartlomiej Wroblewski