The latest physics news is an experimental demonstration of "teleportation" involving both light and atoms, done at the Niels Bohr Institute in Copenhagen, and reported on by the Institutes of Physics and CNN, among others, and remarked on by Dave, among others.
I wrote up some stuff about teleportation in the early days of this blog, and I'll Classic Edition those posts in a little while. "Teleportation" stories always kind of annoy me, though, because the reality isn't nearly as cool as the image that the term evokes. To some degree, it's a triumph of marketing more than a scientific triumph (though it is a cool result).
In this particular case, the thing "teleported" is a weak pulse of light, which is encoded into the quantum state of an ensemble of atoms, and read out a short time later. The slightly garbled descriptions in the news stories end up giving the impression that millions of atoms have been teleported from one place to another, and that is most emphatically not the case. The only thing in the experiment that changes position is light, and it's damnably hard to stop that.
(Details below the fold.)
The basic scheme involves a vapor cell full of cesium atoms, and two lasers. The atoms are prepared in a particular state, and then illuminated with a strong laser pulse. After passing through the atoms, the laser falls on a beamsplitter where it is combined with a second, much weaker laser pulse.
The strong pulse, having interacted with the atoms in the cell, is now "entangled" with the state of the atoms-- interacting with the light changes the atomic state slightly, and interacting with the atoms changes the polarization of the light slightly. After the strong and weak pulses are combined, some measurements are made to determine the joint state of the two pulses (the measurement is slightly complicated, but the basic idea is analogous to flipping two coins and asking whether they're the same or different, without asking the state of the individual coins). The act of measuring the two pulses together entangles the state of the weak pulse with the state of the strong pulse, which was already entangled with the state of the atoms..
The result of the joint measurement is used to determine what signal to send to a radio-freqency coil at the vapor cell. This, in turn, is used to make a small adjustment to the atomic state. Since the atoms are entangled with the light, this lets you encode the state of the weak pulse of light into the state of the atoms, without the weak pulse directly interacting with the atoms themselve. A second pulse from the strong laser is used to "read out" the state, and generate a new light pulse in the same state as the original weak pulse.
This is potentially a very useful technique for quantum information processing experiments, and could be a key component of what Jeff Kimble calls the "quantum Internet"-- if you have two quantum computers in different locations, you might want to transfer information from one to another, and teleportation is a way to do that without destroying the quantum character of the system. This technique also gives you a way to "store" information encoded into light pulses, which again can be useful for communicating quantum information.
However, it's not remotely "teleportation" in the Star Trek sense, nor is it a meaningful step in that direction. The thing that is "teleported" is the quantum state of a light pulse, and nothing more. No atoms are moved from one place to another, and nothing goes faster than the speed of light-- the key step in the process is the classical transmission of the result of the joint measurement to the RF coil, and that happens at light speed or less.
No matter what CNN's mangled syntax makes you think, there's no Star Trek stuff going on here.
