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).