Quantum Candela - project outline

This project is aimed at developing standards for photon metrology from the signal level of existing radiometric standards (1013 - 1014 photons/s, 10-100 microwatts) down to single photons.

This ambitious goal requires a step change in optical metrology in order to bridge the energy difference between the quantum and the classical world. This step change is expected to yield significant improvements over the whole scale, both in uncertainty and in consistency. In the long-term this could result in a reformulation of the candela if such a reformulation could be demonstrably capable of being realised at, and better than, the current accuracy of around 50 ppm (part per million).

project outline

Technical work-packages of the project will address a clear understanding of the limiting effects on a reformulation of the definition of the candela and will investigate the step change of photon radiometry towards a quantum characterisation of single photons.

Work Package 2 - Predictable Quantum Efficient Detector
The objective of this work package is to improve photon flux measurements in the range of 1013 - 1014 photons/s (10-100 microwatts) to an uncertainty level of 1 ppm based on the predictable responsivity of novel silicon photodiodes at liquid nitrogen temperatures. The contents of WP2 will also be of high interest to the semiconductor industry.
Work Package 3 - Linkage to SI (Inernational system of units)
The objective of this work package is to link optical power measurements at the 100 microwatt level to those at the level of one or more photons per second, where optical power is calculated from photon flux using Planck�s law. In this way, the SI will be linked to the single photon regime. A successful linkage will also be a significant step in demonstrating the viability of redefining the candela in terms of a countable number of photons. This will provide the metrology techniques and validation across a broad spectrum of photon detection applications.
Work Package 4 - Single photon metrics
The objective of this work package is to develop suitable metrics for single photon sources and photon number resolving devices, i.e. the methods and the measurement facilities for characterising quantitatively non-classical properties of light like antibunching, indistinguishability, entanglement, and quantumness. This will have impact on the emerging industries of quantum information processing such as quantum key distribution and quantum computing.

The key outcomes of this project are:

  1. Photodetectors with a quantum efficiency predictable with an uncertainty < 10 ppm (WP2)
  2. Detectors with photon number resolution for the measurement of single photon fluxes (WP4)
  3. Sources of single photons with predictable parameters, e.g. number, energy (WP4)
  4. Validated techniques for scaling between low and high photon flux regimes, with uncertainties in the calibration chain of around 100 ppm (WP3)