Halfway - Measuring vibrations

(Photo: Hans Stakelbeek/FMAX)

Name: Han Keijzers (29)
Nationality: Dutch
Supervisor: Professor Leo Kouwenhoven (Faculty of Applied Sciences)
Subject: Study of quantum phenomena in nano-mechanical systems
Thesis defense: In about eighteen months

“If you make a picture of a guitar string, you will know two things: first, the picture will show the exact shape of the string; and second, you will know the exact time the picture was taken. This is an example of a classical mechanical system. Let’s now assume you have a quantum string. Because of another theory of physics, you can’t take such a picture because it’s impossible to know the exact position and the time simultaneously.

I want to study this kind of quantum phenomena. The fundamental reason for this is to know more about when the classical world transforms into the quantum world. The quantum world consists of particles, like photons, electrons and atoms. You can study these tiny particles with lasers, but with nanotechnology you can study them even better.

It’s already possible to measure the vibration of a nanostring that has a diameter of only 1.5 nanometres. If you realize that a nanometer is only one-billionth of a meter, or only about ten small atoms next to each other, you will understand that this is an incredibly small size. By cooling a short nanostring to 25 millikelvin, which is just above the absolute zero point of -273 °C, its mechanical vibration has the smallest possible amplitude. This is called the quantum mechanical ground state.
I can already measure the amplitude of a nanostring vibration with help of radio waves. A disadvantage of this method is that the nanostring becomes warmer, and consequently the amplitude of its vibrations increases. This means it is no longer a quantum mechanical phenomenon.

I’m developing a new method to measure the vibration of a nanostring, but then without this increase in temperature. Hopefully this will be possible with help of superconductors, which are materials that have no resistance to the flow of electricity. Making a sample is the hardest thing to do: it involves placing a nanostring between two superconductors, like one would do when suspending a pencil on top of two books. However, in this case, the nanostring isn’t even visible under an optical microscope, and you cannot grab hold of it easily, either.

Fortunately, working in a strong team helps a lot. I get lots of assistance from my colleagues in the Quantum Transport group. Yet sometimes it’s frustrating to work in one of the best groups, with the best facilities, and still not be able to make a good sample. It’s very difficult to do research on the nanoscale. What I like a lot is that my research is a kind of scientific expedition, in which I can never predict what the outcome will be.”