Towards error-free quantum computing

Toward error-free quantum computing
Toward error-free quantum computing

The basic building blocks for quantum computing are capable of withstanding proven errors

For quantum computers to be useful in practice, errors must be detected and corrected. At the University of Innsbruck, Austria, for the first time a team of experimental physicists has deployed a set of universal calculations on quantum bits capable of withstanding errors, demonstrating how an algorithm can be programmed on a quantum computer so that errors do not occur. result.

Toward error-free quantum computing
Toward error-free quantum computing

In modern computers, errors in the processing and storage of information have become rare due to high-quality fabrication. However, for critical applications, where even single errors can have a serious impact, the fix mechanism based on the redundancy of the processed data is still used.

Quantum computers are inherently much more susceptible to interference and therefore will likely always require a fix mechanism, because otherwise bugs will spread uncontrollably in the system and information will be lost. Because the basic laws of quantum mechanics prohibit copying quantum information, it is possible to achieve redundancy by distributing logical quantum information into a entangled state of some physical systems, such as multiple individual atoms.

The team, led by Thomas Monz of the Department of Experimental Physics at the University of Innsbruck and Markus Müller of the University of RWTH Aachen and Forschungszentrum Jülich in Germany, has now succeeded for the first time in realizing a set of calculations on two logical quantum bits that can be used to perform any activity possible. Lukas Postler, an experimental physicist from Innsbruck, explains: “For a quantum computer in the real world, we need a set of universal ports with which we can program all the algorithms.

Basic quantum activity is performed

The team of researchers performed this set of universal gates on an ion-trapping quantum computer of 16 trapped atoms. Quantum information is stored in two logical quantum bits, each distributed across seven atoms.

Now, for the first time, it is possible to deploy two computing ports on these fault-tolerant quantum bits, which is necessary for a universal set of ports: a calculation operation on two quantum bits (CNOT port) and logic T port, which is especially difficult to perform on error-bearing quantum bits.

Theoretical physicist Markus Müller explains: “Port T is a very basic activity.” They are particularly interesting because quantum algorithms without a T-port can be simulated relatively easily on classical computers, negating any acceleration. This is no longer feasible for algorithms with T-port.”

Physicists demonstrated the T port by preparing a special state in a logical quantum bit and teleporting it to another quantum bit through an entangled port operation.

Complexity increases, but accuracy also increases

In encrypted logical quantum bits, stored quantum information is protected from errors. But this is useless without the calculation activities and these activities themselves are very prone to errors.

The researchers performed operations on logical qubits in such a way that errors caused by basic physical activities could also be detected and repaired. As a result, they implemented the first error-bearing deployment of a set of universal ports on encrypted logical quantum bits.

“Implementing error tolerance requires more activity than error-free operations. This will cause more errors on the scale of single atoms, but nevertheless, test operations on logical qubits are better than error-free logical operations.” Thomas Monz is pleased to report. “Effort and complexity increase, but the quality of the results is better.” The researchers also tested and confirmed the results of their experiments using digital simulations on classical computers.

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

Financial support for the research, among others, has been provided by the European Union within the framework of the Quantum Flag Initiative as well as the Austrian Research Promotion Agency FFG, the Austrian Science Foundation FWF and the Austrian Industrial Federation Tyrol.

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