Power/Performance Bits: Dec. 16

Measuring electrons in silicon
In what is believed to be a first, a team of physicists and chemists based at UC Berkeley, Ludwig-Maximilians Universität in Munich, Germany, the University of Tsukuba, Japan, and the Molecular Foundry at the Department of Energy’s Lawrence Berkeley National Laboratory has captured images of electrons breaking free of their atomic shells using attosecond pulses of soft X-ray light lasting only a few billionths of a billionth of a second.

While earlier femtosecond lasers were unable to resolve the jump from the valence shell of the silicon atom across the band-gap into the conduction electron region, the new experiments now show that this transition takes less than 450 attoseconds.

In semiconductors like silicon, electrons attached to atoms in the crystal lattice can be mobilized into the conduction band by light or voltage. Berkeley scientists have taken snapshots of this very brief band-gap jump and timed it at 450 attoseconds. (Source: UC Berkeley)

The technique allowed individual snapshots to be recorded that can be composed into a ‘movie’ revealing the timing sequence of the process.

More-flexible digital communication
Communication protocols for digital devices are very efficient but also very brittle as they require information to be specified in a precise order with a precise number of bits. If sender and receiver — say, a computer and a printer — are off by even a single bit relative to each other, communication between them breaks down entirely.

Humans are much more flexible. Two strangers may come to a conversation with wildly differing vocabularies and frames of reference, but they will quickly assess the extent of their mutual understanding and tailor their speech accordingly.

Madhu Sudan, an adjunct professor of electrical engineering and computer science at MIT and a principal researcher at Microsoft Research New England, wants to bring that type of flexibility to computer communication. In a series of recent papers, he and his colleagues have begun to describe theoretical limits on the degree of imprecision that communicating computers can tolerate, with very real implications for the design of communication protocols.

The goal is not to understand how human communication works —most of the work is really in trying to abstract what is the kind of problem that human communication tends to solve nicely, and designed communication doesn’t, and try to come up with designed communication schemes that do the same thing.