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Single Photonics and Quantum Information


Quantum-based communication and measurement systems that use novel quantum states of light are being developed around the world. However, the technologies to generate, manipulate, and detect these states of light are inadequate for the emerging applications. We are developing new light sources, detectors, and measurement techniques to address these needs.


Our main focus is the development of single photon technologies for quantum information science and technology. We work closely with the Nanostructure Fabrication and Metrology Project on the generation of novel non-classical states of light and the detection of single photons. Currently, we are investigating the use of nonlinear fibers and nonlinear crystals as a source of correlated photon pairs or squeezed light. We are also manipulating the squeezed light to make Schroedinger "Cat" states of light. In addition to making non-classical states of light, we build detector systems that are the best in the world at operating at the single photon level. Presently, our project is primarily focused on using two different superconducting detector technologies -- transistion-edge sensors (TES) and superconducting nanowire single photon detectors (SNSPD).

Transition edge sensors are cryogenic devices that are capable of detecting small amounts of energy, essentially microcalorimters that measure small packets of energy (absorbed light). If the light is monochromatic (one wavelength), then the signal height is proportional to the number of photons that have been absorbed. Any calorimter has four essential components: absorber, thermometer, thermal weak link, and heat sink or bath. Nature is able to provide all four components in a small thin-film of tungsten. The electrons in the tungsten act together as the absorber. We measure the temperature of the tungsten by biasing the electrons in the middle of their superconducting transition. There is an intrinsic weak thermal link between the the electrons and the atomic lattice (nuclei of the tungsten atoms); the lattice acts as the heat sink.

Major Accomplishments:

  • Demonstrated the highest system detection efficiency for single photons, >95 % at 1550 nm.
  • Demonstrated, with outside collaborators, world-record, long-distance quantum key distribution systems using superconducting nanowire single photon detectors.
  • First demonstration of time-correlated single photon counting with superconducting single photon detectors.
Schematic of TES for photon number resolution and record-high single photon detection efficiency.
Transition edge sensor (TES) for single photon detection or photon-number-resolving detection.

Start Date:

January 21, 2005

End Date:


Lead Organizational Unit:


Sae Woo Nam
(303) 497-3148

Mail Stop 815.04
325 Broadway
Boulder, CO  80305-3328