Single-Photon Sources and Detectors
An essential obstacle and key concern in quantum cryptography and opti- cal quantum computing is the generation of single photons. CQT has been investigating various implementations for solutions to the above. Defects in diamonds have recently been shown to provide an effective means of gener- ating single photons on demand, with an efficiency of over 90%. Diamonds have further been shown to be promising candidates for a solid state quan- tum computer. The principle of operation is associated with the electron and nuclei spin states within a particular implanted defect. Another method of achieving pseudo-single photons is to attenuate a laser pulse, such that on average there is less than one photon per pulse. Although suitable for Quantum Key Distribution, weak laser pulses are not truly single photon sources, but rather a Poisson distribution of photon number states. Such a photon source has been realized and a prototype developed by the CQT. Detecting single photons requires specialised optics and electronics; optimi- sation of the signal from an avalanche photodiode to detect single photons is a key aspect in this research.