Method for spatial filtering of a quantum signal for free-space quantum communication

It is claimed a method for spatial filtering of a quantum signal (6) for free-space quantum communication, preferably comprising a spatial filter (3), a detection means (4), and a calculation means (5) arranged at a receiver (2), whereas the quantum signal (6) for quantum communication is sent via a free-space channel (20) to the receiver (2), and whereas the quantum signal (6) is spatially filtered by the spatial filter (3), in order to reduce the background noise in the quantum signal (6), and whereas the quantum signal (6) is detected by the detection means (4), and whereas a performance metric is calculated from the spatially filtered and detected quantum signal (6) by the calculation means (5). According to the invention, the spatial filter (3) is an adjustable spatial filter (3), and the adjustable spatial filter (3) is adjusted by the calculation means (5) in order to optimize the performance metric of the quantum signal (6).