2 for 1: NIST design enables more cost-effective quantum key distribution

A highly simplified schematic of a recipient's detectors in a quantum cryptography setup. Conventional cryptography setups (left) require at least two detectors, and the most common setup, known as BB84,... Click here for more information.

Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a simpler and potentially lower-cost method for distributing strings of digits, or “keys,” for use in quantum cryptography, the most secure method of transmitting data. The new “quantum key distribution” (QKD) method, outlined in an upcoming paper,* minimizes the required number of detectors, by far the most costly components in quantum cryptography. Although this minimum-detector arrangement cuts transmission rates by half, the NIST system still works at broadband speeds, allowing, for example, real-time quantum encryption and decryption of webcam-quality video streams over an experimental quantum network.

In quantum cryptography, a recipient (named Bob) needs to measure a sequence of photons, or particles of light that are transmitted by a sender (named Alice). These photons have information encoded in their polarization, or direction of their electric field. In the most common polarization-based protocol, known as BB84, Bob uses four single-photon detectors, costing approximately $5,000-$20,000 each. One pair of detectors records photons with horizontal and vertical polarization, which could indicate 0 and 1 respectively. The other pair detects photons with “diagonal”, or +/- 45 degree, polarization in which the “northeast” and “northwest” directions alternatively denote 0 and 1.