  Modern single-photon detectors based on avalanche photodiodes offer
increasingly higher triggering speeds, thus fostering their use in several
fields, prominently in the recent area of Quantum Key Distribution. To reduce
the probability of an afterpulse, these detectors are usually equipped with a
circuitry that disables the trigger for a certain time after a positive
detection event, known as dead time. If the acquisition system connected to the
detector is not properly designed, efficiency issues arise when the triggering
rate is faster than the inverse of detector's dead-time. Moreover, when this
happens with two or more detectors used in coincidence, a security risk called
"self-blinding" can jeopardize the distribution of a secret quantum key. In
this paper we introduce a trigger-disabling circuitry based on an FPGA-driven
feedback loop, so to avoid the above-mentioned inconveniences. In the regime of
single-photon-attenuated light, the electronics dynamically accept a trigger
only after detectors' complete recovery from dead-time. This technique proves
useful to work with detectors at their maximum speed and to increase the
security of a quantum key distribution setup.
