A new type of faster quantum computer

Quantum computing concept

Parity computers can perform operations between two or more qubits on a single qubit.

Parity quantum computers make complicated algorithms easier to implement.

In a quantum computer, quantum bits (qubits) act simultaneously as a unit of computation and memory. Quantum information cannot be stored in a memory like in a conventional computer since it cannot be copied. Due to this restriction, all qubits in a quantum computer must be able to interact with each other. This remains a major hurdle in the development of powerful quantum computers. To overcome this problem, theoretical physicist Wolfgang Lechner, together with Philipp Hauke ​​and Peter Zoller, suggested a novel architecture for a quantum computer in 2015. This architecture is now known as the LHZ architecture after the authors.

“This architecture was originally designed for optimization problems,” recalls Wolfgang Lechner, from the Department of Theoretical Physics at the University of Innsbruck, Austria. “In the process, we stripped the architecture down to a bare minimum to solve these optimization issues as efficiently as possible.”

The physical qubits in this architecture encode the relative coordination between the bits rather than representing individual bits.

“This means that not all qubits have to interact with each other anymore,” explains Wolfgang Lechner. With his equipment, he has now shown that this parity concept is also suitable for a universal quantum computer.

Wolfgang Lechner Research Team

The team was led by Wolfgang Lechner (right): Kilian Ender, Anette Messinger and Michael Fellner (from left). Credit: Erika Bettega (ParityQC)

Complex operations are simplified

Parity computers can perform operations between two or more qubits on a single qubit. “Existing quantum computers already implement these types of small-scale operations very well,” explains Michael Fellner from Wolfgang Lechner’s team.

“However, as the number of qubits increases, it becomes increasingly complex to implement these gate operations.”

In two publications in Physical Review Letters Y physical exam AThe Innsbruck scientists now show that parity computers can, for example, perform quantum Fourier transforms, a fundamental component of many quantum algorithms, with significantly fewer computation steps and therefore more quickly.

“The high parallelism of our architecture means that, for example, the well-known Shor algorithm for factoring numbers can be executed very efficiently,” explains Fellner.

Two-stage bug fixes

The new concept also offers efficient error correction from a hardware point of view. Because quantum systems are very sensitive to disturbances, quantum computers must continually correct errors. Significant resources must be devoted to protecting quantum information, greatly increasing the number of qubits required.

“Our model works with a two-stage error correction, one type of error (bit shift error or phase error) is avoided by the hardware used,” say Anette Messinger and Kilian Ender, also members of the research team at Innsbruck. There are already early experimental approaches to this on different platforms.

“The other type of error can be detected and corrected through software,” Messinger and Ender say. This would allow a next generation of universal quantum computers to be realized with a manageable effort. The spin-off company ParityQC, co-founded by Wolfgang Lechner and Magdalena Hauser, is already working in Innsbruck with partners from science and industry on possible implementations of the new model.

References: “Universal Parity Quantum Computing” by Michael Fellner, Anette Messinger, Kilian Ender, and Wolfgang Lechner, October 27, 2022, Physical Review Letters.
DOI: 10.1103/PhysRevLett.129.180503

“Universal Parity Quantum Computing Applications” by Michael Fellner, Anette Messinger, Kilian Ender, and Wolfgang Lechner, October 27, 2022, physical exam A.
DOI: 10.1103/PhysRevA.106.042442

The research was funded by the Austrian Science Fund and the Austrian Research Promotion Agency.

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