Method and system for quantum key distribution

A method for quantum key distribution, the method being implementable in a system, the system comprising:

• a transmission line for transmitting optical signals between a first data processing device and a second data processing device;
• and
• an optical amplifier disposed at the transmission line, the optical amplifier comprising an active fiber section and a pumping device (16);
• the method comprising:
• determining a ratio between a target maximum gain and a target operating gain of the optical amplifier;
• determining an active fiber section length such that the optical signals with a target maximum signal power are amplified with at most the target maximum gain;
• determining an operating pumping power of the pumping device below the maximum pumping power such that the optical signals are amplified with a target operating gain according to the determined ratio between the target maximum gain and the target operating gain;
• and
• determining a shared key between the first data processing device and the second data processing device by quantum key distribution comprising amplifying the optical signals via the optical amplifier by operating the pumping device at the operating pumping power.