It’s a race of sorts. It’s a race to be the first research team to use quantum teleportation to transmit messages to and from orbiting satellites. The distance of this transmission will be about 500 kilometers. The latest ‘leg’ of this race was just completed by a team of European physicists and published at arXiv [12 May 2012, open access, Quantum Teleportation Using Active-Feed-Forward Between Two Canary Islands]. They achieved quantum teleportation at a distance of 150 kilometers, marking the advance of technology from 16 km to 100 km and now 150 km. Now let’s get to the What and the Why.
Why first: All communication, even with the most sophisticated encryption, can be intercepted and broken. For more than a century there has been a continuous effort to develop the perfect, unbreakable messaging system. None, so far, are perfect although a few are so difficult that for all practical purposes nobody tries to break them. Nevertheless, only perfection promises absolutely secure messaging for the most critical information. So the work goes on. That brings the subject to quantum teleportation and the What.
The word ‘quantum’ should be your tipoff that this is going to be an abstract (no, weird) explanation, but here goes: Let’s say you want to transmit a message between point A and point B. To do this with quantum teleportation, start with two photons, particles of light. Electrons could also be used but most research has involved photons. One of the properties that photons can have is called quantum entanglement. To explain the physics requires a great deal of math, but put in words as simply as possible, when two photons are ‘entangled’ they behave as if they are one photon. If one photon spins clockwise (say, right) then both spin clockwise. In the jargon, each of the two photons is said to have a qubit, a piece of quantum information. If you separate the photons and send one from A to B (this is the hard part), then you have two entangled (identical) qubits, call them (a) and (b).
Let’s say you want to send a different qubit of information (c) from A to B. At point A (c) is joined by a digital operation (say adding 1 or 0) with qubit (a) producing (ac). Because (b) is entangled with (a) it immediately becomes (bc). However, the operation of joining with (c) destroys (a) and (b), leaving only (c) at both places. Down at point B, (c) now exists but it could be in one of four quantum ‘states’ and it’s unknown which one. To find out which one, A sends the two bits used in the digital operation on (a) to point B. B performs the same operation with the two digital bits and that reveals the state of (c), exactly as it is at point A. Message complete. This system is unbreakable because it requires having the original (b) qubit.
Got that? And this is the simple version. The important thing is that it works. Messages using quantum teleportation can actually be sent in the real world. It was first achieved in 1998, using photons in super-cold conditions (near absolute zero). Later it was done with photons at normal temperatures. In 2004 the distance between point A and B was increased to 600 meters using optical fiber, but it was discovered that the glass in the fiber tended to break up the photons and destroy information. Thereafter, experiments were done in the open air. In 2010 a Chinese team used quantum teleportation over 16 km [SciTechStory: Quantum teleportation over 16km in open air]. Again in 2011 the same team increased the distance to 100 km. Now the European team has brought the distance to 150 km.
At each step, new technology was applied to increase the success of transmitting entangled photons from point A to B. This mostly involves advanced laser technology to guide the transmission. Granted the process is crude, more proof of concept than demonstration of application, but the scientists involved all say that the goal of transmitting quantum information to satellites is not only feasible, but likely to happen relative soon. How soon? The scientists are wisely mum, but estimates run from less than ten years to more than three. Quantum teleportation has its mysteries, but like gravity (which we also don’t fully understand), it works.