Universal Parity Quantum Computing, a new architecture that breaks performance limitations

The computing power of quantum machines is currently still very low. Improving performance is a big challenge. Physicists from the University of Innsbruck, Austria, now present a new architecture for a universal quantum computer that overcomes such limitations and could soon be the basis of the next generation of quantum computers.

Quantum bits (qubits) in a quantum computer serve as both arithmetic unit and memory. Since quantum information cannot be copied, it cannot be stored like in a classical computer. Because of this limitation, all qubits in a quantum computer must be able to interact with each other.

This is currently still a major challenge for the construction of powerful quantum computers. In 2015, the theoretical physicist Wolfgang Lechner, together with Philipp Hauke ​​​​and Peter Zoller, took on this difficulty and proposed a new architecture for a quantum computer, which is now called the LHZ architecture after the authors.

“This architecture was originally developed for optimization problems,” says 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 do not represent individual bits, but encode the relative coordination between 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.

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,” write 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.