Laser frequency locking to an optical cavity using LQG control

Systematic approaches to the design of quantum optical systems will become more and more important as their complexity grows. One such systematic technique is the Linear Quadratic Gaussian (LQG) methodology. Here we describe the design and implementation of a LQG feedback controller in a quantum optical experiment - frequency-locking an optical cavity to a laser The successful implementation of the LQG design procedure to this particular problem lays the groundwork for the application of other modem control techniques to quantum optical systems. Our results are promising for future, more complex stabilisation problems in quantum optics, as the described approach is inherently multi-variable and naturally incorporates multiple sensors and actuators as well as nested loops.