Mr Ensslin, the QSIT project launched in 2004 has now been declared a National Centre of Competence in Research. What will this change?
Klaus Ensslin: In the early days we were simply a team of professors from ETH Zurich that set about the scientific exchange of ideas and coordination in the field of quantum science. Now, the research alliance has spread all over Switzerland and we’re glad to receive substantial funding from the Swiss National Science Foundation and home institutions, which enables us to push ahead with our research in the field. We’re proud that the thirty-three teams also include very strong research groups from Basle, Geneva, Lausanne and the IBM lab in Rüschlikon, which means we can really diversify our research.

What do you see as the advantages of the collaboration?
Quantum information processing is a new branch of research that is well developed in theory. There’s a roadmap for the construction of a potential quantum computer, which is usually only typical in industrial developments. We know what we need, but there are various ways to get there: with light, electrons on a chip, atoms or ions. The roadmap shows what’s been achieved so far and with which method. Every method had its advantages. In semi-conductor technology, we know how to build semi-conductors and can do so on a large scale. Today’s semi-conductor chips contain up to a billion transistors that work according to the laws of classical physics. At the moment, we can only produce a limited amount of well-controlled quantum systems based on ions or atoms. For the future, we need to make these quantum systems in large quantities and as similar as possible. Combining optimum properties from different systems could be the key to success.

Could you give us an example?
Using a system based on atoms to process the quantum information while the result is saved in a solid body, on a chip. Communication between the systems could take place with coherent photons.

Is work on this already underway?
That’s all still very much in the future. After all, we still don’t know how to exchange coherent quantum information between completely different systems. So even more exciting than this prospect is the road that takes us there. The NCCR QSIT enables us to tackle wacky ideas like that. The first doctorates in this “combined field” are already in progress. The fact that research is being carried out in all these fields in Switzerland is the strength of both the project and the country: we’ve got specialists in all branches and therefore an enormous range.

So QSIT will exploit this potential fully.
Exactly. Here’s an example: one floor below me, Tilman Esslinger works with cold atoms that are manipulated back and forth using mirrors and lasers; we work with semi-conductor structures on a nanometre scale, a completely different method. The astonishing thing, however, is that mathematically speaking we’re already testing the same equation that describes our physical experiment for the second time – even though we’re doing completely different things. That means there’s an intellectual superstructure where physicists, engineers and especially computer scientists are united with a common scientific goal.

Does that mean you use different approaches and pursue the same goal?
Take electricity; electricity is charge per unit of time and, if we look at it more closely, consists of individual electrons. If I measure these with a detector, it goes click, click, click, but so quickly that I can’t count it. In a circuit we built in my team, however, we have now devised a method to count the electrons; Tilman Esslinger has developed a detector for atoms and, unlike us, counts atoms. Statistics are crucial in quantum mechanical systems. The statistics of the electrons or atoms counted are closely interrelated: we count quantum systems that are completely different and eventually find the same formula behind it.

How does a quantum system differ from a classical mechanical one?
The physical behaviour of quantum systems is described by the Schrödinger equation. You don’t need this to describe a football. Here, many little systems “talk” to one another and the whole system is not coherent. To this day, we still don’t know exactly the system size where the crossover between classical and quantum mechanics occurs: can a virus be quantum mechanical, too? Could I make something I can touch with my bare hands but which is still quantum mechanical? We can’t answer these questions yet.

What advantages do quantum systems offer?
Quantum systems are highly sensitive compared to the macroscopic world. One day, we might be able to build quantum mechanical sensors on this basis that are several orders of magnitude more sensitive than the sensors we know today. Take the classical gyroscope, for instance: it always holds its axis of rotation, even if it tilts; a quantum mechanical gyroscope would maintain this much better. If we used this property for submarines that pass beneath the Antarctic or wherever GPS no longer works, for example, a submarine could use the quantum spin to determine its whereabouts. If I speculate further, in the distant future highly sensitive quantum mechanical sensors – perhaps at room temperature – might be able to measure magnetic bodily signals. QSIT research could yield highly sensitive sensors with uses we can’t even begin to imagine yet.

Can you give us an example?
One example is what we call entanglement, where two particles are correlated quantum mechanically. We can already do this for two or three particles or more, but the leap towards entangling a thousand or even a billion particles is gigantic. We’re still not sure how to. If we manage to do so, we might be able to process complex quantum information. But many other goals are conceivable.

What else other than the quantum computer?
We live in an information society so everyone’s talking about the quantum computer, even though we don’t even know the applications in detail yet ourselves. All the other objectives I could mention are therefore probably wrong. If we knew what they were, industry would already have snapped them up by now. As Nobel-Prize winner Herbert Kroemer once said: “Every discovery creates its own use.” Quantum mechanics is an extremely successful theory and probably won’t change all that much as a result of our research work, but who knows? What is new is that we can use the laws of quantum mechanics to accomplish a particular aim. Applications are bound to arise as a result. After all, when the transistor was invented no one could have imagined the Internet.

How does QSIT work?
We had a launch meeting in Arosa in mid-January where all 170 scientists involved met up. All the professors talked about their plans in the project and where they saw potential links to other groups. The important thing for us was for the doctoral students to discuss their ideas and projects amongst themselves, too, and have an opportunity to get to know each other during an afternoon of skiing. A lot of interesting projects have already come about that way. In future, we want to organise mini-sabbaticals for all doctoral students who receive QSIT funding where everyone experiences a completely different research area once a year for a week.

What are your personal expectations from the project?

I’d like to see a colourful bouquet of outstanding scientific results. With QSIT we’re looking to establish Switzerland on the international stage as a leading research facility in the field. For me personally, it’s important that we create an atmosphere for young people through QSIT in which they find excellent conditions and a scientific environment so they get excited about their subject, enjoy their work and see that it’s a job for the future. Getting good people isn’t hard; keeping them in research, though, that’s a different story.

National Centre of Competence in Research QSIT

In May 2010 ETH Zurich was awarded two new National Centres of Competence in Research (NCCR) by the Swiss National Science Foundation (SNSF). The project “Quantum Science and Technology” run by the professors Klaus Ensslin, Tilman Esslinger (ETH Zurich) and Richard Warburton (University of Basle) was launched in January, just a few months after the project MUST headed by the professors Ursula Keller (ETH Zurich) and Thomas Feurer (University of Berne). A total of CHF 34 million is to be ploughed into the two programmes in the first four years. The projects are spread out over three four-year periods.

QSIT researchers have already managed to chalk up major successes over the past year: the journal Science hailed several studies from the field of quantum mechanics published in 2010 as the research breakthrough of the year. ETH-Zurich professors Tilman Esslinger and Matthias Troyer were involved in two of these publications. The research groups involved succeeded in successfully constructing and testing quantum simulators for the first time. Esslinger’s team, for example, created a new so-called many-body system out of light and atoms which was used to observe and measure quantitatively a fundamental phase transition theoretically predicted by Klaus Hepp (ETH Zurich) and Eliot Lieb (Princeton University) in the seventies for the first time. Matthias Troyer’s team succeeded in using numerical simulations to verify the results of quantum simulations with a supercomputer that could be performed by a similar quantum simulator. The simulator was based on a three-dimensional optical grid produced by laser beams in which specific atoms were captured. All the components of the quantum simulator had to be accurately adjustable so how the system to be simulated behaves could be reproduced. The idea of building a quantum simulator began with Nobel-Prize winner Richard Feynman, who suggested back in the 1980s that complex quantum systems were only be calculable with a quantum simulator.