Error Correction In The Quantum World

Sebastian Krinner is the first Lopez Loreta Prize winner of ETH Zurich. The physicist has a clear goal: he wants to build a quantum computer that is not only powerful, but also works flawlessly.

"Here, at the bottom of this white container, are the circuits," explains Sebastian Krinner with obvious pride, after guiding the visitor through the large space of high-tech equipment. At the very back of the lab of the Quantum Device Lab, the physicist has set up his experiment - and here he will probably spend several hours working in the next few years. Because Krinner receives - this year for the first time ever - the highly endowed Lopez Loreta Prize, which enables him to continue his project at ETH Zurich in the next few years.

Sensitive quantum states
Krinner pursues an ambitious project: As senior assistant in the research group of Andreas Wallraff he wants to take the development of quantum computers a decisive step forward. "When you talk about quantum computers, you usually talk about controlling as many qubits as possible," he explains. "However, it is often forgotten that the qubits as carriers of quantum information do not work faultlessly." In fact, the fragile quantum states can easily be disturbed, so that inaccuracies and false information creep into the calculations.

So how do you manage to keep the error rate as low as possible? Krinner wants to show that this can be achieved with the help of so-called logical qubits. In a logical qubit, several qubits are interconnected so that they work like a single qubit, just more stable and less prone to error.

Complex experimental setup
That sounds simpler in theory than it actually is. On the one hand, the individual qubits must already have a high level of reliability before they are interconnected. If they have an error rate of more than one percent, linking to logical qubits is even counterproductive - the error rate would then rise instead of decrease. On the other hand, the qubits must be linked in a very small space. The control of the flat quantum mechanical elements is thereby much more demanding.

Right now, Krinner is working on linking a few qubits to logical qubits and experimentally verifying their behavior. In the white container, the heart of his pilot plant, the qubits are cooled to unimaginably low temperatures of a few millikelvin, almost to the absolute zero. Attached to a futuristic-looking construction and controlled by numerous fine coaxial cables, the qubits are then connected together in the desired form with respect to quantum mechanics.

A clear vision
Krinner has been fascinated by the world of quantum physics since the beginning of his studies in physics in Regensburg and Paris. And he worked with very different systems during his time at ETH Zurich. As a doctoral student with Tilman Esslinger, he dealt with ultracold atoms as quantum mechanical objects that are trapped and cooled in laser traps. With Andreas Wallraff, he now works with superconducting circuits, which he can present on his office table for demonstration purposes. "There is a lot going on in this work," explains Krinner. "And that's exactly what I like.

Krinner has a clear vision: If the development of logical qubits is going according to plan, he wants to merge these in the second part of the project into an even more powerful quantum computer. "Quantum computers have great technical potential because they are able to solve complex and complex computational tasks much more efficiently than conventional computers," Krinner explains his fascination with his field of research. "And at the same time they are very inspirational from a scientific point of view, because the development of these machines gives us many new insights on how physics works in these areas." But until Krinner can realize his visions, it still needs a lot of groundwork. After all, the Lopez Loreta Prize now gives him the opportunity to hire two Ph.D. students to give his project additional impetus.