# How quantum mechanics threatens our digital lives – and makes them safer

Much of the work of Serge Fehr, Professor of Quantum Information Theory, is abstract and theoretical and comprehensible to very few people. But his work helps make the digital world safer so that in future our internet banking will still be problem free, for instance. He will explain more in his inaugural lecture on 26 September.

Quantum physics, or quantum mechanics, is a scientific discipline that looks at the behaviour of the very smallest particles. It is the theory that describes how atoms, electrons and light etc. behave. It is difficult to explain exactly how quantum physics works. Fehr: ‘I can give similarities or high-level ideas, but they will always be misleading. Quantum mechanics is like nothing we are familiar with. The only way to really understand it is to understand the mathematics behind it. There is no shortcut.’

'If at some point there’s a working quantum computer, much of the current cryptography will be insecure.’

## Difficult to crack

Fehr is working on quantum information theory, which combines quantum physics and information theory, and its applications to cryptography. Thanks to cryptographic schemes from this information theory, we can now do secure internet banking, for example, and our medical records are secure. These schemes are very difficult to crack with today’s computers. ‘But if at some point there’s a working quantum computer, much of the current cryptography will be insecure,’ says Fehr. ‘And there’s a huge effort going into developing that computer.’ In the future quantum computers will be able to make rapid calculations that would take regular computers millions of years, such as factoring large integers in a flash.

Fehr is therefore working with others to develop and analyse new cryptographic schemes that a quantum computer wouldn’t be able to crack. Fehr: ‘I’m researching whether the schemes we want to use are as secure as we think they are. And I do that from a very mathematical perspective.’

## Mathematics

He has loved mathematics since secondary school. What he likes is how maths takes a lot of intuition and imagination but is ultimately really precise. ‘You have to translate everything into strict mathematical formulas. And there is nothing in between. A mathematical statement is true or false. What I also really like is that it’s endless. With every mathematical problem that you solve, new problems pop up and ask to be tackled. The abstract and theoretical side of my work motivates me but it’s a nice side-effect that some of what I do helps make our digital world a safer place.’

Along side his work in Leiden Fehr works for Centrum Wiskunde & Informatica (CWI), the national research institute for mathematics and computer science in the Netherlands.

*Text: Dagmar Aarts
Photo: Unsplash*