Quantum Physics – Copy Protection Thanks to Uncertainty
They are the nerve fibres of our globalized world:
glass-fibre cables and communication satellites relay bits and bytes...
...in the form of light pulses and radio signals around the globe.
Without them, modern communications and a fast Internet would be impossible.
But the transmitted information can be intercepted unnoticed.
Scientists are working to change that...
...with the help of the peculiar laws of quantum physics.
Experiments have shown that this can be done, ...
...by transmitting information in the form of light pulses.
But not as in Morse code, in which information is coded into a series of “light on” and “light off” signals, ...
...but by writing the information directly into wave packets.
Both the amplitude and the phase of the wave packets.
The laws of quantum physics play a key role here.
And this opens up whole new possibilities.
Because the amplitude and phase of a wave packet can’t be precisely determined at the same time.
The physicist Werner Heisenberg formulated this in 1927 in his famous Uncertainty Principle.
This states that in the quantum world, ...
...certain pairs of properties can never be exactly determined simultaneously.
And it is precisely this effect that scientists now want to exploit...
...to achieve quantum-mechanical copy protection.
As long as no one performs measurements – for example with a receiver or by secretly eavesdropping -...
...both the amplitude and the phase of a wave packet are in reality uncertain.
Although measuring the amplitude and phase yields precise values, ...
...those values are random within the bounds of uncertainty.
If a measurement is repeated with an identically produced wave packet, ...
...the result gives a different random value within the uncertainty range.
The original uncertainty packet can therefore only be fully analyzed...
...with the help of a large number of identically produced signals.
And now comes the crux of the matter:
To measure a signal – as when trying to listen in on transmissions – an eavesdropper has only one attempt.
Measuring the wave packet then yields a random value within the uncertainty range.
But the information about the rest of the uncertainty range is lost during the measurement.
The wave packet therefore can’t be copied precisely.
The copy differs from the original.
Physicists speak of the “no-cloning theorem”.
Scientists now aim to take advantage of precisely this effect to protect communications from eavesdroppers.
An unauthorized party wanting to read a transmission unnoticed...
...has to measure the wave packet and then relay an exact copy onward.
But precisely this is impossible.
The act of measuring and copying alters the wave packet.
The eavesdropping attempt is then noticed, and the transmission can be interrupted immediately.
Global quantum communications could therefore make eavesdropping on transmitted data impossible.
