Low cost timing interval analyzers for quantum key distribution

The Bristol free space Quantum Key Distribution (QKD) system offers a potential solution to possible future security problems. Within the Bristol QKD system there is no shared clock between Alice, intended to be a mobile phone chipset and Bob the Quantum Automatic Teller Machine (QATM). Therefore instead of sharing a clock, a Timing Interval Analyzer is used to timestamp all incident photons in Bob. As Alice´s repetition rate is fixed and known, it is possible to distinguish Alice´s photons from that of dark counts and ambient light. The TIA produced in house to do this time stamping process has a resolution of 30.5 picoseconds and a single shot RMS measurement error of 35.2 picoseconds, whilst using off the shelf components. Although the TIA is used within a QKD system it has wider applications within other photonics experiments in particular that of time correlated single photon counting (TCSPC).