Photo: Joachim Rode

Quantum technology defies reason

Friday 24 Nov 17


Ulrich Busk Hoff
Senior Adviser
DTU Physics
+45 29 80 41 55
In the world of quantum physics, things can be in two places at the same time. Postdoc Ulrich Busk Hoff devotes much of his time talking about this fascinating phenomenon.

It is a quite an ordinary morning. The Hoff family is seated around the breakfast table. Suddenly, six-year Bertram moves his chair closer to Ulrich’s, gives him a serious look and says:

“Dad, we need to have a chat about this quantum physics business.”

Other busy parents might be tempted to say ‘later’, but Ulrich is not the kind of person to miss such a golden opportunity—and there, on the spot, he decides to give his son a story about quantum physics.

Ulrich explains that he will also be giving a lecture on quantum technology that same evening—to which Bertram dryly remarks: “quantum technology is a very long word”.

And he is right: the word refers to certain phenomena we do not come across in everyday life, which is what Ulrich finds so fascinating. He does not claim to completely understand the nature of quantum physics. Precisely for this reason he finds it so rewarding to respond to his son’s questions and in general to communicate the subject to other people.

“It forces you to think about everything else you tend to take for granted. We’re really good at describing quantum phenomena in terms of mathematics and conducting experiments that show that our theories hold water. Things can be in superposition—i.e. in several modes at once and ‘entangled’ even though they are located in two different locations. We can’t see it, but we know it must be true. It’s incredibly fascinating—but difficult to understand using conventional concepts.

When we analyse things in the natural sciences, we break them down into small boxes and try to understand them individually. This doesn’t work with entanglement. Here, it’s about the bigger picture—two particles that constitute a system no matter what you do with them—with the exception of measuring them.”

Ulrich has attempted to uncover why it is so difficult for us to understand entanglement by studying the different philosophers—and via Heisenberg. Popper, and Bohm, he has arrived at Kant. So now he is sinking his teeth into Kant’s ‘Critique of Pure Reason’. In general, he likes to read authors who see the world from different angles. This gives him some pictures which are very useful in the communication process.

Close to Nobel physicist

Ever since he was a boy standing in the backyard with his telescope gazing up at the stars in the dark East Jutland night sky, Ulrich has been fascinated by the natural sciences. Finding out how the world works all the way down to the smallest detail. So, naturally, after his secondary school leaving examination, he embarked on a physics degree at the University of Copenhagen (UCPH).

At some point in the course of his BSc he took part in an experiment aimed at condensing a cloud of sodium atoms into a quantum state so that it began to behave as a single object—the so-called Bose-Einstein condensate.

This fascinated the young bachelor student enormously, to the extent that he decided his MSc would centre on quantum physics. However, not content to make do with what UCPH had to offer, he travelled at one point to École Normale Supérieure in Paris where he was allowed to carry out his thesis work in the lab under the tutelage of Professor Serge Haroche, who—six years later—was awarded the Nobel Prize in Physics for his work with experimental methods for measuring and manipulating individual quantum systems.

“Learning from some of the finest academic minds and even being part of some of the group’s publications was a fantastic experience,” says Ulrich without in any way taking credit for any of the ground-breaking results.

“At UCPH, we measured atoms with light—in Paris we used atoms to measure light. Both parts were equally exciting. And ever since it has been a driving force for me to experience how it’s possible to build experiments that are so advanced that you can study nature at the most detailed level.”

"I think that it’s fantastic to both have your fundamental scientific experiments and to take your field of expertise and try and make it understandable to others."
Postdoc Ulrich Busk Hoff, DTU Physics

Photo: Joachim Rode

Why is the sky blue?

After completing his master’s degree, it was only natural for Ulrich to start his PhD studies at the University of Copenhagen—but he stopped because he did not feel at home there. Physics was fascinating, but he could not find his place in the new group.

Instead, he threw themselves wholeheartedly into the job of upper secondary school teacher—and was very happy with his decision. He devised new exercises and continually tried out alternative ways of drawing the students into the universe which so enthralled him.

“I was mildly depressed to discover how narrow a view of the world many of the students had. They were only interested in their immediate surroundings—school, the shopping centre, and activities in the home. So I did everything I could to force them out of their bubble and introduce them to some elements of nature that could hold their interest—like considering why the sky is blue—that’s a question everyone should ask themselves. I wanted to make them aware of the world: Look, here’s something really exciting if you just bother to open your eyes.”

Despite being lured back to the research community after several years as an upper secondary school teacher and completing a PhD at DTU Physics, Ulrich has not stopped communicating his knowledge on many different levels. He still spends a great deal of time introducing upper secondary school students, folk high school students, readers of—and DTU students, of course—to the wonderful world of quantum physics.

“You can argue that it’s academic suicide to focus as much on communication as I have. It takes time away from publication, which is the basis on which we are assessed. But I think that it’s fantastic to both have your fundamental scientific experiments and to take your field of expertise and try and make it understandable to others,” says Ulrich. And an impressive range of communication initiatives underline his point.

Dolph, the hippo

It is thanks to Ulrich that Nanoteket at DTU Physics has been extended with quantum physical set-ups where upper secondary school students and DTU students can conduct their own experiments and see the results for themselves—superposition and entanglement are real phenomena and not just theoretical formulas.

Quantum physics is not part of the curriculum for upper secondary school students, so Ulrich is also developing teaching materials for teachers preparing to organize visits to DTU’s QuantumLab. Ulrich, who believes that it takes more than words to capture student interest, was eager not to produce just another boring textbook. He therefore decided to team up with illustrator Anders Morgenthaler, who he believed would be the best man to balance the complex with the very simple.

“Anders’ quirky look at the world perfectly complements quantum mechanics. Dolph the hippo has always reminded me of a quantum mechanical measurement. When we measure a superposition state and at the same time collapse down into a defined state, Dolph the hippo comes along with his club and forces the quantum state to exhibit a special property.”

Before long, there will also be a book on quantum physics written and designed by the author Jan Egesborg based on several lectures Ulrich and his group leader—Professor Ulrik Lund Andersen—held for him. And looking ahead, the book may develop into a comic strip for slightly older readers.

Structure and recycling

Concurrently with his many communication initiatives, Ulrich is working on new experiments in continuation of his PhD project. His dream is to make small objects behave quantum mechanically by means of light. Although primarily a basic research project, it may lead to new types of sensors or alternative quantum bits. Ulrich has also undertaken to coordinate DTU’s new consolidation efforts in the quantum technology area—Quantum DTU.

Naturally, he has to find time and energy for the family, which is about to welcome child number two in a month’s time. The house is filled with guitars of all kinds, which Ulrich tries to find the time to play and a piano, which he and his son are exploring together—and the family often pops over to the DR Koncerthuset concert hall or other venues to listen to music.

How do you find time for everything?

“I structure my work carefully and make sure to recycle wherever possible. And I’ve discovered I’m fine with just four hours’ sleep—joy and enthusiasm keep me going… and every now and then I enjoy a long nap at the weekends.”


Photo: Joachim Rode

Ulrich Busk Hoff is 35. He is married, has a six-year-old son and is expecting a second child in November. Lives on Islands Brygge in Copenhagen.

2015—Postdoc at DTU Physics, with a six-month break as a postdoc at the University of Queensland, Australia

2015: PhD in physics from DTU

2010: Upper-secondary school teacher training courses, University of Southern Denmark

2007: MSc in physics from the University of Copenhagen

2006: Thesis study at the École Normale Supérieure in Paris

2001: Mathematics student from Odder Upper Secondary School