1 / 2024 // LEOPOLDINA / NEWS 7
“ Quantum phenomena are similar to experiences in normal life ”
Leopoldina Member and physicist Gerd Leuchs spoke at the certificate ceremony for Class I
Gerd Leuchs has been a member of the Leopoldina since 2005 and has been researching at the Max Planck Institute for the Science of Light in Erlangen / Germany since 2009 . In February , the physicist held the public Leopoldina Class I lecture on “ Quantum science and quantum technologies ”. In conversation , he described how he teaches quantum physics and what connects him to the Leopoldina .
The physical laws of the quantum world often contradict our everyday experience . How will you explain this world to your audience ? Gerd Leuchs : In many ways , quantum phenomena are similar to experiences in normal life . For example , it has a lot to do with the superposition of waves of different frequencies , which we also experience with water waves , for example . But in the quantum world , a measurement only results in one of these frequencies . This used to be called the “ collapse of the wave function ”, but today it is more commonly referred to as a projection .
Many listeners will still have problems understanding this . Leuchs : That ’ s why I ’ m going to use a tongue-in-cheek comparison that might help a little : you know those pictures where the brain can switch back and forth – sometimes you see two faces , then a vase . The picture contains both motifs , but when I look at it , I reduce it to one of the two .
What gives many lay people the most headaches is the entanglement of two particles – even if they are far apart , the measurement of one of the particles influences the other . Leuchs : Again , I can only answer with a comparison : If I know that you always wear one red and one blue sock , and I
Gerd Leuchs .
Image : Stephan Spangenberg
see one of them I can predict the other . However , quantum physics goes further , it ’ s difficult to understand in detail – but ultimately , we don ’ t understand gravity either . Why do two distant masses attract each other ? It ’ s just a concept more familiar to us .
Quantum phenomena will increasingly be used in practical applications . Can you give some examples ? Leuchs : There is a lot of talk about quantum computers , but so far , they only exist as prototypes with limited capabilities . The most progress has been made with gravitational waves – the laser detectors for these only achieve their maximum , almost unimaginable accuracy on a quantum scale and have already produced a number of fantastic results .
You are doing research into quantum communication . Can you explain what this is about ? Leuchs : Quantum communication makes the encryption of data more secure . When two people communicate with encrypted messages , they must somehow ensure that they have the same key . Today , most methods are based on the fact that it is difficult to break down large numbers into their factors . But if I send quantum signals back and forth , I can immediately determine whether someone has intercepted the signal – because in quantum physics you can ’ t make a measurement without changing the system .
But to do this , the receiver must receive the identical photons that the sender sent . Is this possible via the fibre optic networks that are commonly used today ? Leuchs : Yes , if the distance is not too great . Otherwise , you need “ quantum repeaters ” to amplify the signals , and these are not yet available in the fibre optic network . Or you can use a direct satellite link .
You have been a Member of the Leopoldina for almost 20 years . What memories do you have of the Academy ? Leuchs : My memories go back even further . My doctoral supervisor , Herbert Walther , became a Leopoldina member in the mid-1980s . The Academy , then still in the GDR , was one of the few institutions open to both East and West Germans , thus linking scientists across the Iron Curtain .
What does the Leopoldina membership mean to you ? Leuchs : If I had founded a company , I could measure my success in terms of profit . In science you don ’ t create commercial products , so success is measured by citations or prizes . And the Leopoldina membership is a great honour . What I particularly appreciate is that you meet other members who are established scientists from very different disciplines and look beyond the boundaries of your own discipline .
■ THE INTERVIEW WAS CONDUCTED BY CHRISTOPH DROESSER