Error-free quantum computing becomes a reality

Error-free quantum computing becomes a reality

Artist’s impression of gate operations on logic quantum bits that are protected from errors by quantum error correction. Credit: Johannes Knunes

The basic building blocks of fault-tolerant quantum computing are explained

Due to high-quality manufacturing, errors during information processing and storage are rare in modern computers. However, for critical applications, where single errors can have serious effects, error correction mechanisms based on redundancy are still used in the processed data.

Quantum computers are inherently more susceptible to perturbations, so error-correcting mechanisms will always be required. Otherwise, errors will spread uncontrollably in the system and information will be lost. Since the basic laws of quantum mechanics prevent quantum information from being copied, redundancy can be achieved by distributing logical quantum information in an entangled state of many physical systems, for example, multiple individual atoms.

The research team, led by Thomas Munns from the Department of Experimental Physics at the University of Innsbruck and Markus Müller from RWTH Aachen and Fürschungcentrum Jülich in Germany, has succeeded for the first time in achieving a set of computations on two quantum logics. Bits that can be used to perform any possible operation. “For a real quantum computer, we need a global set of gates with which we can program all the algorithms,” explains Lukas Postler, an experimental physicist from Innsbruck.

Basic quantitative process realized

The team of researchers applied this global gateway set up on an ion-trap quantum computer with 16 trapped atoms. Quantum information was stored in two logical quantum qubits, each distributed over seven atoms.

Now, for the first time, it is possible to implement two arithmetic gates on these fault-tolerant quantum bits, which are necessary for a global set of gates: an arithmetic on two quantum bits (the CNOT gate) and a T boolean. gate, which is particularly difficult to implement on error-tolerant quantum bits.

The basic building blocks of fault-tolerant quantum computing

The basic building blocks of error-tolerant quantum computing are shown. Credit: Yoni Innsbruck / Harald Rich

Theoretical physicist Marcus Müller explains that “T-gates are very basic operations”. “It is particularly interesting because quantum algorithms without T-gates can be simulated relatively easily on classical computers, eliminating any potential acceleration. This is no longer possible for algorithms with T-gates.” Physicists demonstrated the T gate by preparing a special state in a logical quantum bit and transmitting it remotely to another quantum bit via an entangled gate process.

Complexity increases, but so does precision

In encoded logical quantum bits, the stored quantum information is protected from errors. But this is useless without the arithmetic operations, and these operations are themselves error-prone.

Researchers have implemented operations on logic qubits in such a way that errors resulting from basic physical operations can also be detected and corrected. Thus, they implemented the first fault-tolerant application of a universal set of gates to encoded boolean quantum bits.

Fault-tolerant implementation requires more operations than non-fault-tolerant operations. This will introduce more errors on the single-atom scale, but nonetheless experimental operations on logical qubits are better than fault-tolerant logical ones,” Thomas Munz is pleased to report. “Effort and complexity increase, but the resulting quality is better.” The researchers also Examine and confirm their experimental results using numerical simulation on classical computers.

Physicists have now demonstrated all the building blocks of fault-tolerant computing on a quantum computer. The task now is to implement these methods on larger and therefore more useful quantum computers. The methods described in Innsbruck can also be used on an ion-trap quantum computer in other architectures of quantum computers.

Reference: “Illustration of universal fault-tolerant quantum gate operations” by Lukas Buchler, Sasha Heuen, Ivan Pogorelov, Manuel Rispeler, Thomas Feldker, Michael Meath, Christian D. Marciniak, Roman Stryker, Martin Ringbauer, Rainer Platt, Philip Schindler, Markus Muller and Thomas Mons, 25 May 2022, Available here. temper nature.
DOI: 10.1038 / s41586-022-04721-1

Financial support for research has been provided, among other things, by the European Union under the Quantum Flagship Initiative as well as by the Austrian Research Promotion Agency FFG, the Austrian Science Fund FWF and the Federation of Austrian Industries Tyrol.