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Quantum Cryptography

Quantum Cryptography

In quantum key distribution (QKD), two parties use single photons that are randomly polarized to states representing ones and zeroes to transmit a series of random number sequences that are used as keys in cryptographic communications. This string of numbers becomes a quantum key that locks or unlocks encrypted messages sent via normal communication channels. Because the transmitted photons cannot be intercepted without being destroyed, and the act of interception then tips off the message receiver, QKD is considered the most powerful data encryption scheme ever developed and its codes are, by all indications, virtually unbreakable.

World Record

Although the quantum key distribution technique was not created at Los Alamos, laboratory researchers have taken the technology, quite literally, to new lengths in the interest of national security. In 1999, Los Alamos researchers set a world record when they sent a quantum key through a 31-mile-long optical fiber. While this distance proved sufficiently far enough to create QKD networks connecting closely-spaced government offices or localized bank branches, the system failed at greater distances when signal loss increased to the point at which the photons were absorbed by normal optical fiber noise. To achieve longer distances, Los Alamos researchers developed a free-space quantum cryptography system that could send keys through the air. Los Alamos quantum scientists developed a transportable, self-contained QKD system that used polarized photons to send information through the air for distances of up to 10 miles.

This mobile trailer-based QKD system could be quickly deployed in the field and was capable of continuous, automated transmission in both daylight and darkness. Today, Los Alamos researchers are in the process of taking this technology even further by developing a smaller scale version that is capable of being put on an Earthorbiting satellite for transmitting quantum keys distances of hundreds of miles between the satellite and a ground station.

The Quantum Initiative



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