  Experiments in quantum optics often require a large number of control loops,
e.g. for length-stabilization of optical cavities and control of phase gates.
These control loops are generally implemented using one of three approaches:
commercial (digital) controllers, self-built analog circuitry, or custom
solutions based on Field Programmable Gate Arrays (FPGAs) and microcontrollers.
Each of these approaches has individual drawbacks, such as high cost, lack of
scalability and flexibility, or high maintenance effort. Here we present
NQontrol, a solution based on the ADwin digital control platform that delivers
eight simultaneous locking loops running with 200 kHz sampling frequency, and
offers five second-order filtering sections per channel for optimal control
performance. A comprehensive software package written in Python, together with
a web-based graphical user interface (GUI), makes the system as easy to use as
commercial products, while giving the full flexibility of open-source
platforms.
