"The goal is an experimental quantum computer in the canton of Aargau"

Mr. Aeppli, Mr. Rüegg, the decisive contract for the ETH Zurich - PSI Quantum Computing Hub was signed these days by both sides. How did this collaboration come about?

Aeppli: At ETH Zurich, excellent academic research is carried out. Two research groups there have already created individual quantum bits and interconnected them as well. Now we want to build on this success and scale it up. Scaling up is a classic task in engineering. And that is something we can offer – along with our own academic experience – here at PSI.

Rüegg: This collaboration has long been a wish of ours. And fortunately, ETH Zurich was just as interested in it as we were. Specifically Detlef Günther, vice president for research, and Joël Mesot, who a good two years ago moved on from the directorship of PSI to the post of president at ETH Zurich.

Aeppli: Ultimately it became clear to everyone involved: We, as Switzerland, don't want to miss the boat. The architecture of scalable quantum computers has not yet been found. We want to contribute to solving this crucial question and build up leading expertise, from the very start, here in Switzerland.

Will quantum computers eventually replace all previous types of computers?

Rüegg: Not likely. Quantum computers are not superior to classical computers in everything. But with classical computers, it's a very laborious job to calculate the behaviour of the smallest building blocks of matter – in other words, the quantum world. This applies, for example, to solid-state physics, biology, and chemistry – all of which are central research topics at PSI.

Aeppli: At present we take the complex formulas of quantum mechanics and feed them into classical computers. They can calculate some of it, but for other problems they would simply need so much time that it becomes impossible. In contrast, a quantum computer is itself an implementation of quantum mechanics and thus can directly simulate the processes we want to find out about. That will speed things up incredibly.

Rüegg: Already now we choose the means with which we tackle which calculation problem. If I want to calculate two plus three, I don't use a computer at all, since it's quick to do it in my head. For many other computations and applications, we use PCs, laptops, or smartphones. Today simulations of the weather are carried out on classical supercomputers. But in our laboratories, we are investigating quantum mechanical processes – and it is precisely here that a quantum computer will really bring about a revolution.

So you want to build quantum computers here and also use them at the same time?

Rüegg: That's right. A quantum computer such as what we will realise with ETH Zurich at PSI is not simply going to be finished one day. It will be more of a research platform, which itself will be subject to ongoing development. It will be tested and used, continuously improved and upgraded. Just like we do with our large-scale research facilities in order to always be able to conduct research at the foremost frontier of science.

And will there be mass-produced quantum computers someday?

Aeppli: Maybe not complete quantum computers, not so soon. But I'd estimate that in around a decade there will be mass-produced commercial quantum processors.

Back to the Quantum Computing Hub: What are the concrete steps coming up now?

Aeppli: Now the research groups that will work on-site at PSI are being formed. We are planning three groups: The first will use quantum bits or "qubits" based on ion traps to develop a quantum computer. The second is pursuing the same goal, but on the basis of superconducting qubits. These two groups are tied in with thematically corresponding research groups at ETH Zurich, from where Professors Jonathan Home and Andreas Wallraff are taking the scientific lead respectively. These are the two groups I mentioned at the beginning. For the third group, the position of group leader and professor at ETH Zurich has been advertised, and the person selected will be responsible for determining the research topic.

Three research groups – how many staff members does that translate to?

Aeppli: At PSI, around thirty leading specialists will soon be on staff to carry out this research.

So, quantum computers are based on quantum bits, which have to be interconnected. How many qubits are we talking about and has the Quantum Computing Hub set specific targets?

Rüegg: The first milestone we've set, applying both methods – ion traps and superconducting qubits – is to interconnect around one hundred qubits each. We want to use them in a complementary manner, compare them, and study them.

Aeppli: A real quantum processor would require around ten million raw qubits. So this is a different story. To achieve that would require more like 100 to 200 employees as well as external investors and industry partners. Park Innovaare, which at this moment is being built right next to PSI, could offer very interesting possibilities for collaboration with the high-tech industry.

Rüegg: And that is definitely our long-term goal. In a few years we want to be able to say: In the canton of Aargau, there is an experimental quantum computer. It will offer the scientific community in Switzerland unique opportunities to conduct joint research in the field of quantum computing as well as in its applications.

Interview: Paul Scherrer Institute/Laura Hennemann