Quantum leap to secure passwords
THE phenomenon is so weird and so utterly out of kilter with our experience of reality that even Albert Einstein tried to prove that it was impossible – yet it is the force that holds our bodies together.
Now, after almost a century of stormy controversies and inconclusive tests, physicists are celebrating what looks like the first definitive evidence that quantum entanglement works. The scientists hope that their model could be turned into a device that would allow two people to exchange uncrackable messages.
The idea is at once simple and entirely counterintuitive: subatomic particles can be intimately twinned over vast distances.
This means that if you entangled two electrons in Birmingham and took one of them to Tokyo, simply looking at the Birmingham electron would instantly change its brother on the other side of the planet.
Einstein hated the notion, because it implies that information can travel faster than light, sinking the core tenet of his theory of relativity.
In a 1935 paper, he and two colleagues laid down the gauntlet to any scientists who could prove that it worked, setting out a series of ‘‘loopholes’’ that would invalidate the results.
For eight decades the proof remained elusive, but now a group of British, Dutch and Spanish researchers has revealed that nature is capable of thumbing its nose at the finest minds in physics.
‘‘It’s been a very long trip,’’ said Roland Hanson, professor of physics at Delft University of Technology in the Netherlands, where the test was held.
‘‘After decades of experiments getting better and better and closing the loopholes one by one, this is really the final experiment now. It’s really over.’’
The team showed that if you put an electron in one state, you can instantaneously put its quantum partner in the opposite state even if it is far away.
They set up two tiny diamonds in laboratories 1.3 kilometres apart. The diamonds contained nano-scale chemical flaws that each trapped a single electron.
Under a laser pulse, each electron fired out a package of light called a photon that carried a magnetic signature, known as ‘‘spin’’. When the photons met in the middle, they instantly cancelled each other out and entangled the electrons, leaving one with ‘‘up’’ spin and the other with ‘‘down’’ spin.
Writing in Nature, Hanson and his colleagues propose that people could use entanglement to generate passwords for encrypted messages.
If each party had an entangled electron, the pair could instantly create codes that could not be hacked, because there would be no need to send them via a conventional computer network.