This single-photon sensor could also find applications in quantum cryptography. For interplanetary communication, power restrictions make single-photon detection necessary. For quantum cryptography, the sensitivity makes it possible to send information using single photons, which, in turn, makes it possible to detect eavesdroppers, ensuring that data is perfectly secure.

And just as efficiency would allow for communicating over greater distances in space, so it should extend the reach of quantum cryptography. So far, a drop-off in the number of photons limits the range of quantum cryptography to 100-150 kilometers. But, according to Michael LaGasse, vice president of engineering at the Somerville, MA, labs of MagiQ, which is already commercializing quantum cryptography, a detector as efficient as Berggren's could double or triple these distances. Because of cost considerations, however, LaGasse says the new detectors are likely to find only niche markets, such as in military applications.

One engineering hurdle remains before the sensors are ready for such applications, however. Although Berggren's team has already built and tested these devices, because they are so small, focusing the photons on them is a challenge. He expects, however, that this problem can be solved within two years.

Meanwhile, their tests have added to the understanding of these light-detecting devices in ways that should help other researchers, by establishing design criteria for future devices, says Daniel Prober, applied physics professor at Yale University. "This is a very impressive piece of work and really important for the field," he says.