Monday, March 06, 2006

MS+S: David Awschalom

Man, Santa Barbara is the place to be. David Awschalom has been there for years, and they just added John Martinis to the physics department. In CS, they have Wim van Dam (a quantum computing theorist), and have just added Fred Chong, who is a computer systems architect, strong in both classical and quantum. (There are more groups listed here, too.)

Anyway, David's talk at MS+S...I'm not going to have time to give a thorough accounting of David's talk (and probably couldn't do it justice anyway), but wanted to post a few tidbits. It was titled "Imaging spin Hall effect and current-induced polarization in 2DEG".

David is one of the world's best at imaging spin in semiconductors, among other things. David and his group have shown that it's possible to control spin electrically. This has the possibility to eliminate the need for large magnetic fields to control qubits, which would be a plus because the magnetic fields require a lot of power and hardware, and more importantly, are hard to confine to areas small enough to affect only a single qubit.

The spin is controlled electrically by moving electrons through an electric field at relativistic speeds. This motion changes the field felt by the electron from electric to magnetic, affecting the spin. This is done, generally, by taking advantage of the electrical field created by the epitaxial strain, the strain caused by mismatch of the lattices at the boundary between two materials, and is therefore a static phenomenon.

They are creating spins electrically and monitoring them optically. Numerous other schemes for creating spins electrically have been proposed; two that David mentioned that I managed to catch are Edelstein, Solid State Comm. 73, 233 (1990) and Aronov and Lyanda-Geller, JETP Letters 50, 431 (1989).

One truly startling image (to me, at least) was spins precessing in part of a wire. Moving in one direction, they are fine, turn a 90 degree corner and all of sudden they are moving perpendicular to the B field and begin to precess; turn another corner and they stop precessing. I don't see this image in the couple of papers I'm looking at; it might not be published yet.

The spin creation efficiency is largely temperature-independent, which is good news, and appears to be limited by classical gate speeds rather than any physical process.

A couple of very good papers in conjunction with his student Kato (who did his undergrad under my physics professor Kohei Itoh) are this Science paper and this PRL one.


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