This idea has shown up multiple times. I've never understood how they plan to communicate back, especially with a) gram-scale devices b) moving a significant fraction of the speed of light away from us while being c) multiple light-years away.
"A swarm whose members are in known spatial positions relative to each other, having state-of-the-art microminiaturized clocks to keep synchrony, can utilize its entire population to communicate with Earth, periodically building up a single short but extremely bright contemporaneous laser pulse from all of them."
The probes can get power from the launch laser.
At least that’s the idea I got from talking to some of these folks last year.
KNIGHT: "This is not good."