In short, quantum entanglement occurs when two or more particles, photons, molecules or atoms come together in what can be described as a ‘shared state’. For example, this means that for two interacting particles, one can describe their shared state as a ‘superposition of both individual states’. For us in the Newtonian universe this means that one cannot have any information about this shared state as it is a probabilistic one or one that is said to be indefinite. Now if measurement is made, one of the particles will fall out with a definite value – lets say spin up. Then, according to quantum theory a measurement of the other particle’s spin state will yield a value of spin down. What are the implications here? You might think – instantaneous communication – superluminal communication?! Well, superluminal communication (faster than speed of light) does not really play into the whole idea here as it is incompatible with the basic concept of a quantum state (s) and is more of an action at a distance type of concept. Neither locality (action at a distance) nor entanglement are compatible with each other.
I could say so much more here about this fascinating subject. But getting to the final point; the new distance for the quantum teleportation of ‘qubits’ has increased. Juan Yin and his fellow collaborators reported in a recent paper Teleporting independent qubits through a 97 km free-space channel that they achieved this new free space channel distance over the previous record of 16 km. I guess pretty soon we’ll be looking at secret satellites applying this technology as there is no communication to interfere with. The diagram below illustrates what I mean: