We are developing a suite of quantum tools to address the needs of the photon counting community exploiting the quantum nature of light.

Correlated photons, produced in non-linear crystals by parametric downconversion, offer a direct means of measuring quantum efficiency of detectors and source radiance in the photon counting regime. Work is being undertaken to establish a high accuracy measurement facility for detector quantum efficiency using this approach.

Entangled photons offer greater sensitivity and absoluteness in a number of key metrological applications compared to conventional light sources and entanglement is a vital ingredient in quantum information processing schemes. The Entangled Photon Metrology research theme seeks to develop a high-speed source of single-photons and a source of highly indistinguishable photons, as well as developing the measurement infrastructure to utilise and characterise single- and entangled-photons for metrology and validating quantum information technologies.

Current research activities:

• Establishing a high accuracy measurement facility for the absolute calibration of photon counting detectors.
• Best practice in few photon research.
• Quantum state and process tomography to serve the QIP community.
• Establishing a high accuracy two photon interferometer to measure the indistinguishability of single photon source at visible and telecom wavelengths.
• Development of detection technologies at low power.

If you would like to join an international web community of photon counting researchers please go to www.photoncount.org. This website has been put together by the NPL Knowledge Transfer team to promote networking amongst communities working with photon counting detectors and single photon/low light level sources and also industries that use these technologies for a wide variety of applications. Registration is free.

Publications

1. Cheung, J.Y., C.J. Chunnilall, and J. Wang. Radiometric applications of correlated photon metrology. in SPIE. 2004.
2. Cheung, J.Y., et al., The quantum candela: a re-definition of the standard units for optical radiation. Journal of Modern Optics (Special Issue: Single photon sources, detectors, applications and measurement methods), 2007. 54(2-3): p. 373-396.
3. Cheung, J.Y., A.M. Migdall, and S. Castelletto, Introduction to Special Issue on Single-Photon: Sources, detectors, applications and measurement methods. Journal of Modern Optics, 2007. 54(2-3): p. 137-139.
4. Cheung, J.Y., et al. Measurement of quantum efficiency using the correlated photon technique, extended abstract. in NEWRAD 2005, 9th International Conference on Developments and Applications in Optical Radiometry. 2005. WRC/PMOD, Davos, Switzerland.
5. Cheung, J.Y., et al., Correlated photon metrology of detectors and sources. Proceedings of SPIE, 2004. 5161: p. 365 - 376.

For more information please contact: photonics@npl.co.uk