Paving the Way for Error-Free Quantum Computing

Together with physicists from the University of Innsbruck, a research team led by Professor Markus Müller has demonstrated a set-up for fault-tolerant quantum computing in the lab.

 

For quantum computers to be useful in practice, it is necessary to detect and correct the errors occurig in quantum systems. In collaboration with experimental physicists from the University of Innsbruck, a team from RWTH Aachen University has for the first time implemented a universal set of computational operations on fault-tolerant quantum bits, demonstrating how an algorithm can be programmed on a quantum computer so that errors do not distort the result.

Due to the precision of modern computers, data processing errors have become a rarity. However, for critical applications, where even a single error can have serious consequences, redundancy-based error correction mechanisms are still being used. Quantum computers are much more susceptible to failures and thus will probably always have to rely on error correction mechanisms, because otherwise errors would propagate uncontrollably in the system, corrupting the information processed. As quantum physics prohibits copying quantum information, a logical quantum bit must be distributed among an entangled state of multiple physical systems, such as individual atoms, to achieve the necessary redundancy.

Publication in Nature

A team led by Professor Markus Müller from RWTH Aachen University and Forschungszentrum Jülich and Professor Thomas Monz from the Institute of Experimental Physics at the University of Innsbruck, Austria, has now succeeded for the first time in realizing a universal set of computing operations on two logical quantum bits. They have now published their research results in the renowned academic journa, Nature.

The researchers implemented the universal gate set on an ion-trap quantum computer with 16 trapped atoms. The quantum information was stored in two logical quantum bits, each distributed over seven atoms. Now, for the first time, it has been possible to implement two computational gates on these fault-tolerant quantum bits, which are necessary for a universal gate set and from which more complex quantum algorithms can be composed: a computational operation on two quantum bits (a CNOT gate) and a logical T gate, which is particularly difficult to implement using fault-tolerant quantum bits.

“T-gates are very fundamental operations,” explains theorist Markus Müller. “They are particularly interesting because quantum algorithms without T gates can be simulated relatively easily on classical computers. This is no longer possible for algorithms with T gates.” The physicists demonstrated the T-gate by preparing a special state in a logical quantum bit and teleporting it to another quantum bit via an entangled gate operation.

The researchers have also verified and confirmed their experimental results by means of numerical simulations on traditional computers. The physicists now have all the building blocks for fault-tolerant computing on a quantum computer. The task now is to implement these methods on larger quantum computers to enable practical applications. The methods demonstrated in Innsbruck on an ion-trap quantum computer can also be used on other quantum computer architectures. The research was financially supported, among other funding bodies, by the European Union within the Quantum Flagship Initiative and by the Matter and Light for Quantum Information Cluster of Excellence (ML4Q), which is funded by the German Research Foundation (DFG).

Publication: Demonstration of fault-tolerant universal quantum gate operations. Lukas Postler, Sascha Heußen, Ivan Pogorelov, Manuel Rispler, Thomas Feldker, Michael Meth, Christian D. Marciniak, Roman Stricker, Martin Ringbauer, Rainer Blatt, Philipp Schindler, Markus Müller, and Thomas Monz. Nature 2022 doi: 10.1038/s41586-022-04721-1