If you have never heard of what is termed a quasiparticle before, it is understandable if the remark about listening in to the smallest elements of our existence sounds strange.
But in the same way as the better known photon is an individual particle of electromagnetic radiation such as light, sound can also be broken down into its smallest possible unit – the phonon.
And like other phenomena in quantum physics, the sound particle is also governed by the laws of quantum mechanics.
In the past couple of years a completely new area of research has opened up within the field of physics called quantum acoustics. This area now occupies more of Delsing’s time than anything else.
“Five years ago I had no idea that we would be working on this today. We are currently carrying out experiments to investigate quantum fluctuations in sound particles – fluctuations which can be described as sound arising out of nothing and then disappearing again the next moment. As far as I know, nobody’s done this before. I’m hoping that we’ll be the first.”
In 2017 it will be twenty years since he became a professor of experimental physics at Chalmers, ‘specialising in tunnelling and single electronics’ as it was then called in the description.
This is roughly how he would describe it himself in condensed form:
“We manufacture extremely small electronic circuits that we then cool down to a really low temperature. They then become superconductive, in other words the electric resistance disappears. Then we send an electric current through the component and try to understand what happens.“
One particular thing that may happen is that an individual electron gets through an artificial barrier which it should not normally be able to pass through.
That this still does occur, with a certain degree of probability, is associated with the laws of quantum mechanics and with the fact that an electron is not only a particle but also a wave.
“That is precisely what is known as quantum tunnelling. That was where I started and essentially it’s also what I’m still doing.”
But just as a quantum system can remain perfectly still, Delsing has done the same as a researcher.
“I’ve moved from electrons to photons and now to phonons as well. But all the time it has been individual particles and their quantum properties that have been my great interest,” he says.
Why is this so interesting?
“For me the reason is pure inquisitiveness. I want to understand how quantum physics works. It runs counter to our intuition, but why does it do that? I find such questions fascinating. And now and then when you make a discovery and find out something that was not understood before – that gives you a great deal of pleasure.”
So when Delsing and his colleagues in the MC2 lab now carry out what appear to be strange experiments such as allowing sound to interact with superconducting artificial atoms, the aim is quite simply to find out what happens in this case.
“Electrons, photons and phonons are really only different tools, which when combined can give a more complete picture of what quantum interaction is.”
Delsing has been a devoted experimentalist throughout his career, although he does claim to ‘understand some theory’. He therefore likes to interact with theoretical physicists and particularly with Professor Göran Johansson, who is just a corridor away from him in the MC2 building.
“It’s quite unusual in the world of physics research for practicians and theoreticians to work so close to one another. Göran often anticipates what we measure – and suggests things that we could measure. And we often publish jointly.
Although at heart Per Delsing brings the perspective of a fundamental researcher to his work, his research touches upon one of today’s really great potential inventions – the quantum computer. It’s potential, since no universally recognised and general quantum computer has yet been built, even though more than three decades have passed since the idea was born.
“It was a transformative scientific breakthrough when it became clear that the type of extremely small electronic circuits which I and many other physicists experimented with could also be used as quantum bits or qubits, in other words as building blocks in a future quantum computer,” Delsing explains.
This was at the end of the 1990s. To start with they had qubits, which researchers then designed with great care in laboratories throughout the world. The performance was terrible from a computing perspective: the desirable quantum state collapsed after only a couple of nanoseconds – in other words within two billionths of a second.
It wasn’t possible to do much proper calculation work in such a short time.
Today, nearly twenty years later, researchers create quantum systems which can be controlled much better and which ‘last’ for up to 100 microseconds – or one ten thousandth of a second.
This may still sound like an incredibly short period of time, but Delsing points out that this is an increase of four or five orders of magnitude – a dramatic improvement.
The number of calculation operations that can now be performed is significant. Despite this, the problem is in maintaining the quantum state – known as the coherence time – in existence, one of the biggest challenges in the work on implementing a usable quantum computer. You would naturally want to create a computer in which the quantum state could be maintained as long as the calculation required.
Quantum computer researchers are seeking to achieve this via what is termed error correction.
“On a standard computer it’s quite easy to correct errors by allowing several circuits to do the same calculation in parallel. If four then display the same results, whereas the fifth displays something else, you can be quite sure which answer is correct,” explains Delsing.
However, a quantum system is so sensitive to disruption that it collapses if you try to read it. Therefore errors have to be detected and corrected via indirect methods – it’s a bit like spying and tinkering instead of looking and adjusting.
“There are now ideas as to how correction could work. It’s envisaged that many, perhaps hundreds, of qubits will be linked to a logical qubit,” explains Delsing.
The idea is that you can then let several physical qubits collapse while correcting an error – but without the entire quantum system collapsing.
Other major and difficult problems associated with a future quantum computer have more to do with the costs: the ancillary equipment required to be able to send signals to each individual qubit in order to handle the huge quantities of data that arise is likely to be extremely expensive.
Nor does cooling down the quantum computer to slightly above absolute zero come free of charge.
Nevertheless the basic technology has now come far enough, according to Delsing, that it looks as though a functioning and usable quantum computer could actually become a reality in the foreseeable future.
“But it will take at least ten years before we get there. The quantum computer belongs to that category of inventions which is extremely difficult to realise, but where the potential benefit is very great at the same time.”
He therefore welcomes the escalation of interest in the development of a quantum computer on the part of Google, IBM, Microsoft and several other major companies – like the current flagship initiative on quantum technology which is being prepared in the EU.
For his own part Delsing does not describe himself as a quantum computer researcher, even though the research he does is to some extent relevant to the development of a quantum computer.
But what does it mean for a fundamental researcher when such a momentous application starts to cast its shadow over your own research field? Is there a risk that the quantum computer will become an argument for utility, a kind of ballast that you are forced to carry around?
“Yes, sometimes it can feel just like that. Especially when you are seeking funding,” he admits.
“There are special grants you can apply for to carry out research into quantum computers. So sometimes we have to reason as follows: we now want to do some research since it’s scientifically relevant. How can we describe it in terms of quantum computers?
“If the application is granted, a dilemma can arise, especially if the researchers discover something new and exciting which they didn’t expect.
“Can we really spend time on this new area when we have promised to do what we got the funding for? In practice, we usually resolve this by doing a bit of both,” he observes.
However, right now Delsing is well funded and feels that he has a great deal of freedom to do research on what he finds interesting. For example, a few years ago he was appointed a Wallenberg Scholar and in 2015 he was appointed a Distinguished Professor by the Swedish Research Council, with its associated ten years’ funding.
“If I get an idea that’s really interesting, I can do what I want without any further ado. It’s important for all researchers to have at least some ‘free funding’ of this type, I think.”
In the vision for the Area of Advance which Delsing’s group belongs to – Nanoscience and Nanotechnology – there is talk of ‘solving societal challenges’.
Does this objective affect what you take on? How much benefit to society do you actually provide?
“There is a spectrum between fundamental research and technical applications and it’s clear that my research lies closer to the former. But society needs both – and that also applies to the Area of Advance,” he replies.
“You can also view all research as being applied and useful. The question is only how long a time horizon is involved.”
He adds that fundamental research not infrequently produces spin-offs, which can be of practical benefit even in the short term:
“One example from our research that is topical just now is a new type of quantum-based amplifier, which produces an extremely low noise. The Mölndal-based Low Noise Factory – a company with its roots in other MC2 research – is very interested in starting to manufacture such amplifiers,” Delsing explains.
Most people are agreed that a future quantum computer has the potential to be useful to society in the long term. But Delsing believes that it will take some time before the person on the street feels that it has improved their lives.
“There’s much to indicate that the first ‘benefit’ that a completed quantum computer will provide is to simulate quantum systems for us quantum researchers.”
Text: Björn Forsman
Photo: Anna-Lena Lundqvist
Published by kind permission of Chalmers magasin, where it was included in issue number 4 2016.
FACTS – PER DELSING
Born in 1959, grew up in Skåne, studied engineering physics in Lund.
PhD at Chalmers in 1990, where he then stayed on as a researcher and teacher in the field of nanotechnology and quantum physics.
Professor since 1997, elected to the Royal Swedish Academy of Engineering Sciences in 1999. Member of the Royal Swedish Academy of Sciences since 2007 and also a member of its Nobel Committee for Physics, which selects Nobel Prize winners, until last year (‘one of the most enjoyable and all-round educational tasks I’ve had’).
Acclaimed among other things for experiments demonstrating that light can in fact arise from a vacuum (the dynamical Casimir effect, 2011).
Married to Désirée, a language teacher, four grown-up daughters, lives in Landvetter.
In his leisure time: Travel, preferably in combination with downhill skiing. However, summer is spent at his holiday home in the Bohuslän archipelago and then it’s tennis instead of skiing.