A new, faster type of quantum computer

Quantum Computing Concept

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

Parity quantum computers make it easier to implement complicated algorithms.

In a quantum computer, quantum bits (qubits) function simultaneously as arithmetic unit and memory. Quantum information cannot be stored in a memory like in a conventional computer because it cannot be copied. Because of this limitation, the qubits of a quantum computer must all be able to interact with each other. This is still a significant obstacle in the development of powerful quantum computers. To solve this problem, theoretical physicist Wolfgang Lechner proposed a novel architecture for a quantum computer in 2015 together with Philipp Hauke ​​​​and Peter Zoller. This architecture is known today as the LHZ architecture after the authors.

“This architecture was originally designed for optimization problems,” remembers Wolfgang Lechner from the Institute for Theoretical Physics at the University of Innsbruck, Austria. “We reduced the architecture to a minimum in order to solve these optimization problems as efficiently as possible.”

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

“As a result, not all qubits have to interact with each other,” explains Wolfgang Lechner. He and his team have 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). Photo 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 are already very good at implementing such operations on a small scale,” 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 Verification Letters and Physical Check Athe Innsbruck scientists are now showing that parity computers can, for example, perform quantum Fourier transformations – a fundamental component of many quantum algorithms – with significantly fewer calculation steps and therefore faster.

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

Two-stage error correction

The new concept also offers hardware-efficient error correction. Since quantum systems are very sensitive to disturbances, quantum computers have to continuously 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 flip error or phase error) is prevented by the hardware used,” say Anette Messinger and Kilian Ender, also members of the Innsbruck research team. The first experimental approaches are already available on various platforms.

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

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

“Applications of the universal parity quantum calculation” by Michael Fellner, Anette Messinger, Kilian Ender and Wolfgang Lechner, October 27, 2022, Physical Check A.
DOI: 10.1103/PhysRevA.106.042442

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

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