The spooky action-at-a-distance just got a lot longer – over six times longer. Though, the phenomenon is not yet ‘Beam me up, Scotty’, the improvement is heartening. A team of Chinese researchers have teleported qubits across a distance of 97 kilometers, using the phenomenon of entanglement.
The spooky entangled world
Entanglement is a purely quantum-mechanical phenomenon, which started on its road to stardom and fame within the physics community and outside it due to a thought experiment by Einstein.
Here it is in simple terms and closely in the same spirit as Einstein, Podolsky and Rosen had first put it. Take two electron. Now, if they are in the same quantum state, one has to be in an ‘up’ spin state and the other in a ‘down’ spin state. The two spins cannot be the same, because another fundamental principle of quantum mechanics – the Pauli exclusion principle – forbids that. Now, take one electron and separate it from the other by a very large distance – say half the universe – but without ever ‘looking’ at it to see what spin state it is in. Now, take the electron near you and look at it to determine what the spin is. But if you know that, you immediately know what spin state the other electron is in! In other words, you get the information about the farther electron instantaneously, violating the fundamental postulate of relativity which forbids the transfer of information faster than light speed.
To EPR or not to EPR
There has been plenty of debates on this so-called EPR paradox. It remained a thought experiment until Alain Aspect and his group actually performed the experiment and found that entanglement is a very real phenomenon. That hasn’t doused the debates though, with people trying to determine what information actually means and whether information is actually transferred.
Now, the Chinese team uses photons, just like Alain Aspect’s team did in their pioneering experiment. They created two entangled photons, using a 1.3 watt laser, and made them appear at two distinct places separated by as much as 97 kilometers!
Now, a photon can represent a quantum state – or a number of quantum states, really – and can thus be thought of as a ‘qubit’ or quantum bit. It carries a ‘bit’ of information, just like a ‘bit’ on the hard disk of a computer. So far, the researchers have been able to transmit the ‘key’ to a encrypted message, but the message itself needs to be sent via classical channels. It’s like mailing a locked treasure-chest and sending the key to the lock via a quantum mechanically entangled channel.
The work has just been put on ArXiv and here is the link: http://arxiv.org/abs/1205.2024