A 1-year adventure
Wubs started as a postdoc at DTU in 2009, and now 15 years later he’s been appointed professor.
Wubs travelled from his home country of the Netherlands to Germany for a postdoc position. Whilst there he was offered two jobs – one at a quantum computing company in Canada, and one at the Niels Bohr Institute in Denmark.
He chose NBI, which is how he came to Denmark.
It was a short contract, and he and his wife considered it an adventure leaving everything behind, thinking it would just be one year. Well 1 year turned to 17 – and still counting.
When asked why he ended up staying for so long, Wubs explains that he likes the work environment and the huge hub of nanophotonics here – adding that being able to bike to work is a nice perk. About DTU he says that he enjoys being amongst inspiring people saying: "You should not be afraid of other people in the corridor making great discoveries". He adds that this probably isn't the right place for you, if you wish to be the only talented person, explaining how he’s constantly inspired – if not by coworkers then by students.
Starting off strong
When asked about his proudest achievements throughout his career, Wubs highlights a paper based on his PhD thesis, about how two or more atoms can emit light together in a nanophotonic environment. This was one of the very first pieces that looked into this matter. The professor adds that it might have been a bit ahead of its time, as it receives more attention now, than it did around its publishing.
This particular piece of work also played a large part in Wubs' motivation to stay in science.
Wubs explains that this paper allows us to find out conditions for when atoms can emit together, and when they can't. Amongst other things this “emitting together” or superradiance is useful in lasers and in quantum technology.
Wubs' research adds to the understanding of the quantum state of light in materials, so it's the foundation on which a lot of technologies are built – technologies a lot of people are trying to exploit. Wubs' group is trying to study new light emitters in 2D materials, quantum emitters for example.
Challenges in the field
The challenge with quantum-anything is that quantum properties are easily lost, meaning that decoherence is the enemy of any quantum physicist.
To understand quantum decoherence, let’s start with quantum coherence.
At a simplistic level, coherence can be thought of as a part of the information that a quantum system can hold. More precisely, it is a measure of the relationship between different possible states of the system called superposition. This enables a quantum particle to be in two places at the same time, for example. Quantum computers rely on this information to function.
If the system is isolated, coherence is conserved. Decoherence occurs when the system interacts with its environment. This means that the information that the system contains gets mixed up with its environment, making that superposition “collapse” and the system ends in a state where the useful quantum information is gone.
Wubs states that in theory you could make a robust kind of quantum technology, even though the systems you have are not perfect, if you can implement quantum error correction. This does require low levels of decoherence to begin with, and there are other challenges to be overcome. Fortunately, not all quantum technology requires error-free operation.
Wubs' calls his group “pretty explorative”, so they're trying new kinds of emitters in 2D materials, because they think there could be an advantage there. For example, there are now lossless optical cavities smaller than anyone could imagine, developed in our very own NanoPhoton Center, but they're so small that you can't put just any kind of quantum emitters in there – standard quantum dots don't even fit in it. So there's been made something so nice and so small – an immense breakthrough – but now we need to find out what kind of light sources to put in there. And that is (amongst other things) what Wubs and his group, in collaboration with others in the NanoPhoton Center, are trying to figure out.
Controlling quantum dots
The major issue with standard quantum dots is that they are produced in random positions. So you might have very good single-photon emitters, but it will still be very difficult to control where the quantum dots will actually appear. Wubs describes it as people on the beach “you don’t know exactly where they’re going to sit”.
A common solution is to start out with a surface on which you create quantum dots by the usual processes. Then you just observe the random distribution of where the quantum dots have decided to appear, and build the rest of your nanostructures around them.
But that is not ideal for industrial purposes – if you need many of these emitters. Some colleagues at the department are becoming better at controlling quantum dot positions. Wubs and his team take a different route and look for promising types of novel emitters in 2D structures. One of their goals is to create a grid of quantum emitters.
But first, they have learnt to make their nanolamps in 2D and are identifying their microscopic structure. Some radiate visible light and are related to crystal defects of the 2D material. Another ultrathin light source emits close to telecom wavelengths and basically consists of two different atomic monolayers on top of each other.
Wubs is also fond of another collaborative project where they study how these new tiny lossless optical cavities can trap nanoparticles at precise locations, based on the fact that light in these cavities exerts a force on particles. The group collaborates with health researchers and are developing nanophotonic sensors to detect biomolecules.
Papers and people
But the research itself is not the only area for which Wubs has goals. Another main focus of his is to get his group members out as good scientists – he considers this a source of pride just as much as the research. Both the papers and the people.
And of course we're spitting out scientists all the time, it's built into the very fabric of a university, but it sounds like a human resource nightmare, because you educate young people, they get research expertise, and then they leave – typically at a very productive stage.
Even though the system, especially the short and packed PhD curriculum, is not optimized for research output alone, Wubs isn’t bothered “If your papers were the only output, yes that would be a nightmare, but since people are also the output, and they come out steadily, then I still think things are going well”.
What he finds important is that they are a group.
Even though Wubs is the group leader, he does not consider himself the source of all wisdom at all. For Wubs communication is key, because different group members do different things and they all need to understand each other.
Theory, experiment, fabrication are all different things, but getting a feeling of what the others do and how they can help each other is important.
What Wubs sees as an important task for him as a group leader: to be aware of whether things are going well, or if they're missing out on potential.
“Often we are described as nerds – there may be some truth in it”, Wubs ends the interview, but he makes it clear that “in order to truly become successful here, you need to be more than that”.
You need to be a teamplayer – and a nerd.
