Quantum Money

[dreamdancer 0]

interesting...

Quote

THERE is something special about cold, hard cash. Perhaps it is that its value is guaranteed by the government of the day, or that you can stash it under the bed when a banking collapse threatens. Maybe it is the freedom that cash allows: the ability to live without banks or credit cards or taxes.

Quantum physicists think a lot about cash. Not just any old money, you understand. They think about quantum cash. Quantum banknotes aren't like credit cards or dollar bills. They are simply information: a mixture of bits - the 0s and 1s that we use to send electronic transactions - and quantum bits, or qubits, that are governed by the laws of quantum mechanics and can be both a 0 and 1 at the same time.

Since quantum money is just information, it can be stored and transmitted just like a digital picture or a text file. But because it has quantum properties too, it cannot be copied. It is this combination that makes quantum cash so attractive: whoever is in possession of it has exclusive and unequivocal ownership of it, just as with hard, physical cash and unlike a credit card. That is not the only use for quantum cash, though. To physicists, quantum cash is a toy problem, a sort of test case with which to study the strange properties of quantum mechanics.

Now the theoretical foundations are almost in place that could one day allow quantum cash to become a reality. These techniques could potentially be useful for other applications, too, such as making software impossible to pirate.

The idea of quantum money was first suggested in 1968 by Stephen Wiesner, a physicist then at Columbia University in New York. He envisaged creating a banknote containing light traps that could somehow store a few dozen photons. Being quantum objects, photons can never be counterfeited thanks to something called the no-cloning theorem. This states that quantum objects can never be perfectly copied since any measurement of the original also destroys its ability to be a 0 and a 1 at the same time and forces it to be one or the other.

In Wiesner's scheme, the polarisation of these photons would act as a unique identifier for the banknote. These polarisations would be known only to the bank, so anybody wanting to check the authenticity of the banknote need only take it to their local branch, which would use its prior knowledge of the polarisations to check it. And since the photon states cannot be copied, neither can the banknote.

http://www.newscientist.com/article/mg20627562.700-schrodingers-cash-minting-quantum-money.html

stay away from moving propellers - they bite
blue skies from thai sky adventures
good solid response-provoking keyboarding