A Secret In Light

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What is the best way to tell a secret? Whisper it as quietly as possible. How quietly is that? Richard Hughes, 47, a researcher at the fabled Department of Energy lab in Los Alamos, N.M., and the preeminent researcher in the mind-bending field of quantum cryptography, speaks as softly as can be--in single photons of light. Combining cutting-edge encryption with the arcana of subatomic physics, Hughes designs coded messages that can be neither broken nor intercepted.

Here's the problem: codes only work if both parties, sender and receiver, have the key--and at some point they have to pass that key between them in an unencoded form. As a result, all conventional cryptosystems are theoretically vulnerable to eavesdropping. Here is the solution: embed the key in a series of single photons in such a way that the laws of quantum mechanics prevent it from being intercepted. It's perfect.

Hughes runs his experiments in the rugged, volcanic Jemez mountains that surround Los Alamos--which, as an ultramarathon runner, he knows intimately. He sets up a laser and fires a burst of light so precise it consists of a single photon. The photon flies at (what else?) the speed of light to a finely calibrated receiver 2 km away, which collects it like a catcher snagging a Randy Johnson fastball. By sending a series of photons polarized at different angles, Hughes can transmit information: each particle represents a single bit--a 1 or a 0, in computer language.

The result is an untappable line of communications. It would be easier for a potential eavesdropper to pick a single snowflake out of a blizzard than to track down a single photon in flight. What's more, like snowflakes, photons are fragile: according to the surreal logic of quantum physics, the very act of observing one alters it irrevocably.

Mad science? Not at all. Hughes, who was born in Liverpool but is an American citizen, believes we will see quantum cryptography in everyday use within a couple of years, and not only ground to ground but from the earth to satellites in orbit. For a guy who works with subatomic particles, he certainly doesn't think small.