I have been doing a bit of light reading on space telescopes and have been amazed by the reported sensitivity of some of the instruments. In particular, the Laser Interferometer Space Antenna (LISA) which is said to be able to detect a relative change in displacements of 20 picometres over a distance of 1 million km. I'm keen to understand what is the technology/underlying physics behind detectors such as this?
I understand that this is a very broad question as detectors are chasing many different things but a general overview will suffice.
If possible, specifically, what gives rise to the phenomenal resolution of LISA?