Universiteit Leiden

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Hielco Kuipers

Where does the quantum world end?

With his ice-cold nano force sensor, Tjerk Oosterkamp searches for the boundary between the quantum world and the everyday world. The Leiden physicist has received an NWO subsidy of 600,000 euros.

World record

Oosterkamp is working on a force sensor that very accurately measures magnetic forces at temperatures of 273 degrees below zero. He initially developed this sensor for another project. 'We are developing a new type of MRI scan to image virus particles,' he says. 'Such a MRI works with a force sensor that detects magnetic force and has to have a very high resolution of 2 nanometers.' The 'world record' is currently at 5 nanometers. Oosterkamp wants to break this record by placing the force sensor in a very cold environment. 'Heat makes the force sensor vibrate and causes it to be less accurate. Our force sensor goes as low as 10 milliKelvin and by this, we hope to achieve the required resolution.'

The force sensor (picture by Martin de Wit)

Crazy quantum mechanics

Oosterkamp discovered that the set-up could also be used to answer more fundamental questions. Using a spinning electron, he is able to study the fundamentals of quantum mechanics. 'As a physics student, you learn that quantum mechanics is crazy: particles can be in several places at the same time or simultaneously rotate in two directions. But, when you do a measurement, there is only one measurement outcome. I’m looking for experiments that can determine what causes this.’

In two places at the same time

‘Electrons will simultaneously attract and repel the sensor, because they rotate both clockwise and counterclockwise. If our magnetic force sensor itself is a quantum particle, it will move in two directions at the same time. You should see this in an interference experiment in which you manipulate the electron a number of times. This allows the force sensor to first reach several places at once and then interferes with itself. This is also the way in which a double-slit experiment has shown that electrons can be in several places at the same time.’

Where lies the tipping point?

If this is not the case, it means that the sensor behaves like a measuring device and not as a quantum particle. And that is interesting, according to Oosterkamp. 'That would mean that an electron is still a quantum object, but our sensor of a hundredth nanometer no longer is – even if it is made up of electrons, among other things. If that is the case, we will come a bit closer to the answer to the question: what causes the quantum mechanics to collapse at that moment? Does a particle or object have to become very heavy or very complicated? Or is something else going on?’

Free will     

According to Oosterkamp, the beauty about quantum physics is that it shows that reality is much more complicated than people think. 'We want to describe and explain everything around us using the laws of nature, as if everything were one big complicated machine. This can go so far that people say: “man has no free will, because everything is predetermined by the laws of nature." But on a philosophical level, it is not so unambiguous. At the level of quantum mechanics, these laws of nature are really bizarre. So that gives a lot of possibilities for interpretation. Quantum mechanics teaches us that it is not all that simple, and therefore there is no reason to assume that free will does not exist.

Support from the field

With his grant, Oosterkamp will hire a PhD student and a postdoc. ‘I am very happy we have managed to get this grant,’ he says. ‘This means that my colleagues agree that it makes sense to ask this question. This used to be a matter for pensioners, because you would not get any further and would got bogged down in philosophical pangs. The fact that I now get the money to do this experiment actually means that the field says: “the technology has progressed so far that it has now reached a point where we can try to investigate this phenomenon.” The thought of being able to do something about that question, makes us very motivated. At the same time, you know this question has been existing for a hundred years and no answer has been found all this time. So let’s remain modest.'

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