“I’m a ‘Hans im Glück’ – fortunate, as they say.”

Hans Schüssler – pioneer of the ion trap, passionate researcher, and long-time summer guest at the MPQ. An obituary.

Hans Schüssler was deeply fond of international collaboration. As a professor at Texas A&M University, he pursued research across the globe — from the USA and Canada to Japan and Qatar – mentoring generations of young scientists along the way. Every July, for decades, he returned to our institute and enriched ongoing research with his insights and experience. Now, at the age of 93 he has passed away. In the following, Theodor Hänsch remembers his long-time companion, followed by excerpts from a conversation we had with Hans Schüssler at the MPQ in 2023.

A lifelong companion

By Theodor Hänsch

“Sixty years ago, I was a student at Heidelberg University. That’s where I met Hans Schüssler, who was then the supervisor of our advanced physics lab. Since then, our paths have crossed many times.

At the MPQ, he was always a welcome guest – a pioneer of ion trap physics who offered valuable advice on our experiments and enriched lab life with his humorous anecdotes.

Even after his 90th birthday, Hans – greatly supported by his wife Zohreh – remained full of energy and enthusiasm. He used to joke that in his realm of global collaborations, the sun never set.

With his keen insight, openness to new ideas, and dedication to mentoring young scientists, he inspired many. He will be dearly missed.”

Better two such women than one Nobel Prize

In Conversation with Hans Schüssler

Today is your last day here. You’ve spent three months with us — what did you work on during that time?

I was facilitating, as they say. A long time ago, I started an experiment with trapped ions together with Thomas Udem and Ted Hänsch. We aimed to study an atom even simpler than hydrogen – helium 4+. It has two protons and two neutrons, but only one electron. Because the spins cancel out, it doesn’t have hyperfine structure, which makes spectroscopy much easier. We cool the helium 4+ with beryllium ions – it’s like air conditioning for the ion trap! (laughs) It sounds simple, but the required laser wavelength is in the XUV range at 60 nanometers. Generating that kind of intensity is a challenge. For me, it brings things full circle. As a young physicist, I measured the hyperfine structure of helium 3+ – without lasers! And now, decades later, young researchers are working to measure helium 4+ even more precisely.

 

You’ve been visiting the MPQ almost every year — how did it all begin?

Ted Hänsch and I go way back to our days in Heidelberg. I was a research assistant, and he was a student. I supervised him – so he was almost my student. (smiles) When Ted received the Nobel Prize, I happened to be at the MPQ. We heard it on the radio and rushed into town (to LMU Munich) to celebrate. I still remember him, in a tie and freshly cut hair – he looked very proper. The rector came rushing in, saying: “Professor Hänsch, you must stay! Even if you reach retirement age, we’ll do everything to keep you here.” I remember that well. And Ted flew to the U.S. that same afternoon while the reporters were still waiting for him.

You have many anecdotes from your time at the institute — any that particularly stuck with you?

Oh, there are plenty. Back then, we were developing the first linear ion traps at the MPQ. I had a student I worked closely with. On days with good whether and cumulus clouds, we’d look out the window and say, “Let’s head to Unterwössen!” There’s a glider airfield. So off we went – not to the lab, but flying. He’d sit in the back, I in the front, and we’d do aerobatics – yes, even loops! But you can’t exceed 6G, or you’ll black out. Later, Professor Walther stormed into my office: “Are you keeping my students from their work?” I have no idea how he found out. But a couple months later we got even...

At the Ringberg conference, that same student was to present our new linear trap. We had just finished building it, barely in time. Everything was still on slides back then. We showed our results, but we also showed something else… (laughs) ...a photo of the MPQ parking lot. It was strictly regulated – only professors were allowed to park on the one side. And we had parked in Walther’s spot. During the talk, he yelled, “WHO IS PARKED IN MY SPOT?” And the student replied, “There are others who work even when the professors aren’t around.” That was our little comeback — and Walther laughed. So yes, we always also had our fun back then.

What makes the MPQ so special to you?

The MPQ is one of the world’s top institutes in every way. For me, it’s a scientific paradise – a real fountain of youth. I talk to lots of people here old and young, relearn old things, and discover new ones. I’ve forgotten plenty over the years. Everything is so well organized here – double and triple checked. In the U.S., things are more functional, but here, it’s just beautiful. I’m a ‚Hans im Glück‘ (German idiom for ‘a lucky guy’) – fortunate, as they say.

And how did you first get into physics in the first place?

It started early. As a schoolboy, I used to mix chemicals on our balcony – things would spill over, and the whole floor turned red and blue. But my mother let me do it all. That was in the 1940s, just after the war. We boys also cracked open artillery shells and lit the gunpowder. That’s how the experimenting started and the interest in science.

Later, as a student, I read Scientific American – there was an article about how to build an electron microscope. I wanted to see an atom! But to do that, I needed a special glass vacuum chamber. So I went to see Hans Kopfermann himself, the top professor at Heidelberg, and asked if I could request a glassblower. He asked, “What do you want to do?” I said, “I want to see an atom.” He replied, “Well, then go ahead and try!” It didn’t work out at the time, but years later I actually saw an atom – with an ion trap. You can trap barium ions and see their fluorescence with the naked eye. Sadly, Kopfermann had already passed away at that time, but that’s how I got into ion traps.

You truly light up when talking about physics...

Yes, and I could never have done it all without my wife’s support. I’ve been very lucky. We’ve been married for over twenty years now, and my first wife supported me too. Honestly, I’d say it’s far better to have two such women in life than to win a Nobel Prize! (laughs)