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Quantum Cryptography: "The Only Guaranteed Form of Secure Communication"

In a paper published in the journal Science, quantum physicists have demonstrated the randomness of quantum mechanics also applies to the measurement of a particle’s angle and rotation, which also creates new opportunities for increasing bandwidth in quantum cryptography — an ultra-secure way of communicating secretly that can intrinsically detect third-party interception.

Quantum cryptography relies on the strange rules of quantum mechanics, as exhibited by "entangled particles" where the condition of one is instantaneously reflected in the other even if they are separated by a great distance — a phenomenon called ‘nonlocality.’ Thus, by measuring one particle, you can know the condition of the other.

The outcome of a measurement on either particle seems random, but the measurements of both always agree with each other and it is this agreement that can be used to transmit a secret message — making quantum cryptography the only guaranteed form of secure communication.

Einstein did not like this randomness and famously said, "God does not play dice ..."

However, modern physics disagrees and now the research by the University of Glasgow scientists and their colleagues shows that the randomness of quantum mechanics also applies to the angles.

According to Miles Padgett, Professor of Physics at the University of Glasgow, “God does play dice. It has been difficult to show this is the case with angle because angles are problematic: No one can agree on how to measure them. If I say an angle is 10 degrees, you might say its 350 degrees. It depends on your starting point.

“The fact that an angle can take many different values means that each particle of light, a photon, can be encoded to carry the whole alphabet, potentially increasing the data rate of quantum cryptography — the only guaranteed form of secure communication.

“It is guaranteed because you can detect when someone is attempting to read the message because the very act of an unauthorized measurement of an entangled photon destroys the message,” he said.

The research paper, entitled "Quantum Correlations in optical angle-orbital angular momentum variables," is published in the latest edition of Science.

—University of Glasgow Press Office

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