August 2008

EEEL Sets Record for Detection Efficiency with Single Photon Detectors

Researchers in the Optoelectronics Division of EEEL have demonstrated a record-high system detection efficiency of 95 ± 2 % in counting single photons in the near-infrared wavelength region. Adriana Lita, Sae Woo Nam, and Aaron Miller (guest researcher from Albion College) designed, fabricated, and evaluated fiber-coupled, superconducting transition-edge sensors (TESs) optimized for absorption at the telecommunication band wavelengths of 1550 nm and 1310 nm. TESs are capable of detecting visible and near-infrared light at the single-photon level and also demonstrate photon-number resolution; i.e. discrimination between one and two-photon (and higher) absorption events. Single-photon detectors with high detection efficiency, photon-number-resolving capability, and very low noise are required for many applications in quantum information, including photon source and detector calibration, long-distance quantum key distribution, photon-based quantum computing, and n-photon state quantum optics experiments.

The superconducting transition temperatures of the latest TES (178 ± 5 mK) are higher than those for the previous generation of TES, enabling thermal recovery times as short as 800 ns, a factor of five less than the previous decay times. The TES can be optimized for high detection efficiency at particular wavelengths from near-ultraviolet to near-infrared by designing and integrating additional thin-film layers that enhance the absorption of light in the active device material, which for this demonstration was a tungsten thin film of 20 nm thickness. Because the measured absorption of the device structure is very close to the measured system efficiency, it is highly probable that the efficiency can be increased beyond 95 % by fabricating the optical structure with tighter control over layer thicknesses, a higher reflectance mirror at the wavelength of interest, and self-alignment schemes for eliminating the residual fiber-to-detector coupling losses.

For more information contact: Sae Woo Nam, phone 303-497-3148