Extended Data Fig. 5: Schematics of the detection and blinding-attack monitoring circuit.
From: Entanglement-based secure quantum cryptography over 1,120 kilometres
The biased voltage (HV) is applied to an avalanche photodiode through a passive quenching resistance (Rq = 500 kΩ) and a sampling resistance (Rs = 10 kΩ). The avalanche signals are read out as click or no-click events through a signal-discrimination circuit. The blinding signal monitor is shown in the dot-dash diagram. A resistor-capacitor filter and a voltage follower are used to smooth and minimize the impact on the signals. The outputs of an analogue to digital converter (ADC), at a sampling rate of 250 kHz, are registered by computer data acquisition (PC-DAQ). R1, resistor; C1, capacitor; OA, operational amplifier.
