quantum computing

Another interesting topic I've been thinking about recently is quantum computing. Professor Jeff Kimble from Caltech came to give a talk at MIT two days ago. He's one of the people responsible for quantum teleportation. The way that works is pretty funny: the first person, Alice, takes some unknown quantum state and entangles it with some quantum source; then she measures it, which destroys the unknown quantum state, and then sends the classical result over a normal communication channel; then the recipient, Bob, "subtracts" the result from the same quantum source and viola! he regenerates the original quantum state. The original proposal in in this paper: Bennett et al., Phys. Rev. Lett. 70, 1895 (1993). Obviously it's a cool application. Note that it has to obey special relativity, i.e., if Bob gets impatient and tries to guess what Alice is sending him, then the state that he constructs is a random mixture of all four possibilities, which conveys no information. It's also interesting to note the way in which the information is transmitted: clearly, one can't encode a 2-state quantum system with two classical bits of information. However, on the other hand, the quantum source in this example doesn't know anything about the unknown quantum state Alice was using. So what you've done here is split up the information into a completely classical and a completely quantum-mechanical piece, which can have all kinds of implications for quantum communication, calculations, information storage, etc.

On a lighter note, this work was featured on the Daily Show a number of years ago (back in the days of Craig Kilbourne). They said that it was a really good application if you're a beam of light and you need to get from one side of the optical bench to the other. I guess they must have been pissed about that since they called Prof. Kimble a "quantum creep". :-)

In the next post, I'll talk about some of his recent work and how it ties into one of my current research projects.