And the reason it matters that this is a single pixel at two billion times per second is that we can hypothetically stack many of these assemblies on top of each other and get video of a single event that is not repeatable.
What you've invented there is a camera sensor :) Silicon photomultipliers do exist and are used in some LIDAR applications. The bigger problem would be creating the 921600-channel oscilloscope to capture all this raw data.
