Skip to main content



Ulf Leonhardt: transforming optics research

19 Jun 2019
Taken from the June 2019 issue of Physics World. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

Best known for his work on invisibility cloaks and “transformative optics”, Ulf Leonhardt from the Weizmann Institute of Science in Israel talks to Joe McEntee about science in Israel, his career – and his new novel

Ulf Leonhardt

How has transformation optics evolved over the past decade since the initial breakthroughs on invisibility cloaking?

The research on invisibility and related effects has become much more diverse – and that’s a good thing. In the long run, I think the applications will not be in optics but in areas like acoustics and other mechanical waves. Essentially, we’re talking about the manipulation of waves with ideas taken from transformation optics and inspired by analogies with space–time geometries. Imagine, for example, you have a bridge and you want to protect or cloak that bridge from potential earthquakes. How do you design the surrounding underground structures to effectively minimize the effect of seismic disturbance? That’s a meaningful question and an active area of endeavour. Acoustics applications are driven by military requirements such as the cloaking of submarines and other naval vessels from sonar. This is not something I’m working on, and even if it was I wouldn’t be able to talk about it!

What are your research priorities at the moment?

Transformation optics is an active area for my group in various respects. One example is the idea of transforming the geometry of space in optical instruments – and specifically planar silicon photonic devices. Fundamentally, this is about shaping light at the chip level and what we can add are some unique design tools and manufacturing tools. This is work that’s heading in an applied direction for the sorting of light on chips in optical switching and optical computing technologies.

Any other areas?

Another theme is the connections between transformation optics and Casimir forces – the forces of the quantum vacuum that are responsible for “stickiness” in nature. Though tiny, Casimir forces become significant at micron and submicron distances. They’re the reason parking tickets attach to a windscreen and, unhelpfully, why parts in nano- and microelectromechanical systems sometimes stick together. There are deep, unresolved problems in this field and it’s worthwhile working on them. It’s subtle, challenging research and it’s off the beaten track. We’ve found surprises already and there will be plenty more that will lead to new and interesting lines of enquiry.

What attracted you to Israel and the Weizmann Institute?

So far, I’ve worked as a researcher in 10 countries, including Germany, where I was born, as well as the UK and Sweden. I came to Israel to settle in 2012 and have invested lots of time and energy in setting new research directions. For now, it looks like a life sentence – the nice sort of life sentence. The Weizmann is an institution for basic research and the most important criterion is that the science is interesting – nothing else. Whether the work leads to some additional funding or practical applications is of a secondary nature. Having said that, there’s a paradox here in that the Weizmann is also the world’s most successful scientific institution in terms of research commercialization. Patent income is a huge part of the financing model.

What is the secret of that success?

It’s because the best applications come from fundamental science. The Weizmann Institute is a graduate university – we have no undergraduates – and a lot of the drive comes from our students. They have an eye for applications, innovation and want to spin off companies – and it helps that the Weizmann has strong ties with industry on many levels. There’s also the commercial environment in Israel, with a significant proportion of GDP – in excess of 30% – coming from hi-tech industries.

What sets the Weizmann Institute apart from other institutions you’ve worked at?

The Weizmann is an institution of international significance with a predominantly Israeli student body and faculty. The quality of our students is a big differentiator. A Master’s thesis here will typically involve 12–18 months of research and the final output is at the level of a UK PhD. For PhD studies, four or five years is completely normal and the research stands in comparison with elite institutions around the world.

How does this help to set students apart?

It’s worth noting that most of our students have been through a period of military service after high school – three years for men, two years for women. As such, they will have worked on science and technology R&D programmes from an early age, often with significant responsibility for budgets and delivery. When they join us at the Weizmann, our students are already mature, independent, responsible and prepared to take ownership – significant attributes when pursuing a postgraduate research path.

Prior to Israel, you spent 12 years at the University of St Andrews. What impact do you think the Brexit impasse is having on UK science?

I know from several senior colleagues in the UK that they are thinking of leaving or have concrete plans to leave because of the uncertainty around Brexit – especially with respect to EU research funding. It makes me very sad because traditionally the UK has been very attractive and welcoming as a destination for European scientists, including myself. The language, the openness of the research institutions, the value placed on individual freedoms: all these factors have made the UK an easy place for foreign scientists to settle and work, while providing a window to the wider world within Europe. It all depends how the political situation works out over the next few months, but right now there’s a serious problem. No doubt about that.

Having spent some time working in China, how do you see the country’s global emergence as a science superpower?

There’s a major debate right now – driven by the trade war with the US – about the global rise of China and what the West must do to respond. China plays a long game, including in science, with government support and co-ordination of that long-term outlook. Europe and the UK – which is still a part of Europe – need to be ready for the challenge before the Chinese Belt and Road Initiative begins to stretch its tentacles into European science, as it has already done in Italy. We live in interesting times, and they will get more interesting by the day. It’s time to wake up.

Do you have any advice for early-career scientists embarking on their chosen research path?

If you want to achieve something difficult in science, you must first believe in it. You cannot be a critic from the outset; if you are, you’re not getting anywhere. At the same time, there’s an important duality or paradox to remember – on the one hand believing something is possible, on the other only trusting the facts and being self-critical at the appropriate time. In my team, we are our own strongest critics. In research, you also need to be patient and to persevere through difficult times. Although, when you find that a given line of enquiry isn’t working you should be honest and true to yourself. Be prepared to write it off and start all over again.

If you want to achieve something difficult in science, you must first believe in it

You have also written a novel. What inspired you to do this?

I have always enjoyed writing stories in foreign languages and so, one rainy winter day in Israel, I began writing a novel. Storytelling is the natural, most human way to communicate and teach anything – even physics. Aspiring novelists are usually advised to write about things they know well, so I wrote a story about the science I do and about travelling the world off the beaten track.

What is it about?

The book is about the science of invisibility and optics more generally. The reader will get an accurate picture of the real science of invisibility and glimpses into different cultures. If a publisher is interested, I would be happy to talk terms.

Copyright © 2020 by IOP Publishing Ltd and individual contributors