Scientists have long wanted to use photons to send secret keys, but until now the technology hasn't been precise enough. Theoreti-cally, each 1 and 0 of the key could be encrypted on a single photon, then randomly polarized at some known angle--anywhere from straight up and down to perfectly flat. Eavesdropping would require intercepting the photons, copying them, then sending them on their way. Since due to quantum mechanics, it's impossible to perfectly measure a photon's polarization, an eavesdropper will find himself in a quandary: Unsure of the photons' original states, he must guess when he retransmits them. His mistakes potentially alert the message's recipient to the tampering. But recipients have lacked a way to assess incoming single photons, so they were effectively blind. Enter Nam. His device detects single photons by reading the faint heat pulses they generate in superconducting tungsten cooled to 1/10 of a degree above absolute zero. One might expect the maker of such a precise machine to be a cautious type. But Nam likes to dye his hair odd colors and has been known to enter a 200-mile bike race on the spur of the moment. His former adviser, Stanford physicist Blas Cabrera, says that, thanks to that energy, Nam does the work of three. "I like thinking about lots of random different things," Nam says, most unprecisely.