June 2005

EEEL Scientists Demonstrate High Efficiency Single Photon Detector

Scientists in the Quantum Electrical Metrology Division and the Optoelectronics division in the Electricity and Electrical Engineering laboratory have demonstrated a single-photon detection system with a quantum efficiency greater than 88 percent. This represents a significant increase in detection efficiency that could contribute to the development of practical quantum computers and secure quantum communications. The device also could enable new studies aimed at testing fundamental principles of quantum mechanics such as a complete loophole-free test of Bell's inequality. The detector operates at the wavelength of near-infrared light (1,550 nm), often used for fiber optic communications and produces negligible false (or dark) counts. The active element of the sensor is a tungsten film that is biased into its superconducting-to-normal transition after being cooled to 100 milliKelvin. Absorption of a photon creates an increase in temperature that can easily be measured. By embedding the detector in a stack of optical elements designed to enhance the absorption in the tungsten, the researchers have more than quadrupled the photon detection efficiency from 20 percent for a bare tungsten film in the past year.

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Sae Woo Nam, phone 303-497-3148