‘This is Elsa.’

PhD candidate Dennis Uitenbroek is tinkering away at a several-metre-high setup built around a large cylindrical tank – a so-called cryostat. Beneath the structure lies a rug with an image of the famous Disney snow queen.

‘I was in a silly mood, so I bought this on AliExpress.’ He points to other tanks in the lab: ‘We named them after Frozen characters. That’s Marshmallow, and that one is Olaf.’ The lab also features a Frozen Lego set and an Olaf stuffed toy.

Uitenbroek works in the Oosterkamp-Hensen Lab, named after the two professors in charge. The measurement hall is a labyrinth of scaffolding, wiring, pipework and computer screens. It is also blessed with high windows, offering a view of the greenery along Wassenaarseweg. 

The main attraction: cryostats. These thick-walled vessels can cool experimental setups to extremely low temperatures. This allows us to observe quantum mechanics: the behaviour of the tiniest particles in the universe, such as atoms and molecules. Quantum mechanics predicts, among other things, that particles can teleport, or exist in multiple places at once – a phenomenon known as ‘superposition’. The latter is what they are trying to achieve in the measurement hall.

‘Trying to create quantum behaviour is very difficult,’ explains PhD candidate José Dupont. ‘There is always some interaction with the environment, through vibrations or heat, for example. All forms of heat are disruptive, so we want to cool the system to extremely low temperatures. Using clever tricks, our cryostats can bring the setup down to a few millikelvins.’ Those temperatures are below -273 degrees Celsius, close to absolute zero.

FLOATING OBJECTS

Vibrations from the outside world are effectively filtered out by placing each cryostat on a block of concrete weighing twenty thousand kilograms. These sit in the basement beneath the lab, resting on four large car tyres. A cryostat can be lowered on top of such a concrete island via a square opening on the ground floor.

For additional isolation, the physicists sometimes make objects float here. Witold Kamphorst, a bachelor’s student in physics, is working on this for his final project: ‘I’m trying to make increasingly smaller magnets float in order to eventually reach quantum scales.’ He points to a cryostat: ‘Ultimately, you want to place it in a nice fridge like that.’

Dupont: ‘Our vibration isolation is unique in the world. We need it to be because we’re standing on peat soil, which isn’t very stable.’ Despite all the measures, passing buses are still subtly visible in the measurements.

The ultimate goal of this lab is not only to observe quantum effects, but also gravity – and to do so simultaneously. For her PhD, Dupont is studying the theoretical background of these experiments. Her being involved in the lab is unique, she says. ‘There have never been full-time theorists here before. They usually stay in their own bubble. I get to see how things really work here, and that will hopefully make me a better theorist.’

With pen and notebook in hand, she explains: ‘There are two theories about the universe: quantum mechanics and the theory of gravity. These operate on completely different scales.’ Physicists apply one at the atomic level, the other to planets and larger systems. ‘But what’s not clear is whether these theories could work together on a human scale.’ 

DIVIDED OPINIONS

The combination of these two theories is known as ‘quantum gravity’. Dupont: ‘Opinions are still very divided as to what exactly that is. We are exploring the various theories with our setups.’ To do so, they aim to bridge the gap between gravity and quantum mechanics. This means that gravity must be scaled down to ever smaller dimensions, and quantum mechanics to ever larger ones.

The ultimate goal has not yet been achieved, but the researchers are already carrying out remarkable experiments: ‘We’re working on equipment to bring objects with a size of a few micrometres into superposition.’ For comparison: a human hair is one hundred micrometres thick. For humans, this is minuscule, but it is roughly a million times larger than an atom – a typical quantum scale. Uitenbroek has already managed to detect miniature gravitational forces: ‘We measured that a small lump weighing half a milligram was attracted by the gravity of a two-kilogram block.’

Every day, researchers tweak and tinker with the setups. ‘You always start with a trial-and-error approach’, says PhD candidate Loek van Everdingen. And that results in error, he continues. ‘In practice, you’re more concerned with the question “which wire has broken now?” than with what quantum gravity is. After a while, the research becomes a bit less sexy.’ 

He compares his work to that of a plumber. Cooling is provided by a tangle of pipes: ‘They can sometimes burst, and if that happens after working hours, the whole place can flood overnight.’ Fortunately, this water does not flow into the lab, but into the basement – a space the size of a few classrooms combined. ‘Once, there was a layer of three centimetres of water here.’

‘HALL OF FAME OF FAILURES’

Then the whole lab has to help out, water vacuum cleaners in hand. ‘We once pumped 56 wheelie bins’ worth of water out of the basement’, adds PhD candidate Martijn Janse. A sign with 56 tally marks can be admired in a glass display case in the middle of the lab. ‘This is our hall of fame of failures’, says van Everdingen. Inside the cabinet are burnt-out cables and coils, among other things. A Delft blue tile bears the words of wisdom: 

Live
Laugh
Heat conduction improves with patience

‘You should also be proud of the things that go wrong’, Janse believes. ‘When people hear the term physics, they tend to think of the theoretical side, where everything works out exactly using equations. But when you actually go into the lab, nothing works. The reality is never that simple.’

It creates a trade-off between speed and robustness. ‘If you take a very long time to make everything perfect, you’ll never be able to take a measurement’, says Dupont. According to Janse, the setups do not need to win any beauty contests. ‘It just has to work. We’re not Apple with an aesthetic product design. That costs too much time – time we’d rather spend on physics.’

LITTLE GLAMOUR

The researchers do not expect to witness quantum gravity during their PhDs. ‘Our current quantum systems need to become a hundred billion times more massive before we can measure their gravity. That won’t be possible for another thirty years’, says Dupont.

Not everyone has that kind of patience, according to professor Tjerk Oosterkamp. ‘People sometimes become very unhappy about the lack of results. Sometimes, a PhD candidate quits in their final year. I’ve seen that happen twice.’ He always emphasises to applicants that there is very little glamour involved. ‘There are plenty of people who planned to do a PhD here, and after my warning they say: “Maybe it’s not for me.” I think I warned José too late.’ ‘I’m still smiling’, she reassures him.

For Janse, such a long-term project is actually a relief. ‘I find it a hopeful thought that in science we still dare to dream on the long term, especially at a time when everything is getting faster and faster and the average attention span is a TikTok video. Projects like this really advance science.’