Quantum cryptography has been around since the 1980's but up until now only very small packets of information have been able to be encrypted at one time. Now a breakthrough that identifies the angle and rotation of photon particles is taking this technology to the next level.

Since the first working prototype of a quantum transmission device (PDF) was produced in 1989 only binary data has been transmittable. Move forward to 2010 and researchers have unlocked the potential of quantum cryptography by developing a technique that allows the transmission of more complex messages.

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Scientists at the Universities of Glasgow and Strathclyde in the U.K. and Rochester in the U.S. have discovered that the randomness of quantum physics also applies to the alignment of photons, and that the rate and angle of rotation of a photon particle can be measured.

“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,” said Professor Miles Padgett, Professor of Physics at the University of Glasgow. “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.”

The technology works because of a phenomenon called nonlocality, a strange law of quantum mechanics exhibited by what are known as entangled particles, where the condition of one is instantaneously reflected in the other, even if they are separated by a great distance.

In quantum cryptography nonlocality is achieved by splitting a light particle – called a photon – through polarization. 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 message.

When Einstein first observed nonlocality he didn't believe it was due to instant communication between the two particles, as this would violate his laws of relativity given the information would need to travel faster than the speed of light. He called it "spooky action at a distance" and thought that this showed quantum mechanics theory was incomplete. Modern quantum physics has proven Einstein wrong, although it is still not fully understood how nonlocality works.

Via: University of Glasgow

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