Scientists Demonstrate Long Distance Quantum Communication
The August experiments both used fiber optic cables to transmit the entangled photons, solving the problem of how to get them to the remote location. In addition, the researchers were able to test another property of those entangled particles, which is that they can provide powerful, perhaps uncrackable encryption. This is because when the entanglement takes place, it generates what is effectively a key, and the key must be transmitted to the remote site before the results can be read. While it's possible to intercept the entangled particle, doing so without the key is useless. In addition, even if you send the intercepted particle on its way to its intended recipient, the fact that its state was observed cannot be concealed. Ultimately, the recipient will know that the particle was intercepted, revealing the hack attempt. While all of this may seem far-fetched, it's not. The concept of quantum communications is in its early infancy. But it's promising enough that the Chinese government has already launched its first satellite designed to test whether the signals it transmits cannot be hacked and to test other properties of quantum communications in space. It will be no problem to use that satellite to determine for sure whether faster than light communications are possible. Other work needs to be done before the full capabilities of quantum communications can be determined and then turned into real uses. Among other things, the scientists working on the communications problem are also trying to see if there are limits to distances, and how long an entangled particle can be preserved before it's used.What's not known is whether this precision is really necessary to send an encryption key to the other end to determine the state of the entangled particle and whether there are other factors that will affect how the entanglement works. If some or all of those limitations can be overcome, then quantum communications could revolutionize communications as we know it. Right now, most scientists will say that some limits, such as the need to send a key, cannot be overcome. But as I said, it's still early and it wasn't very long ago when this whole area of study was dismissed as impossible. The use of quantum encryption is most likely to become available in the near term because it's effectively become an engineering problem, not a problem of theoretical physics. Beyond that, more research is necessary. Nobody knows how to do it just yet, but researchers are working on the problems.
Right now the particles are being sent over lengths of fiber that are identical, so that they will appear at the other end at exactly the same time.