  The generation of time signals is a fundamental task in science. Here we
study the relation between the quality of a time signal and the physics of the
system that generates it. According to quantum theory, any time signal can be
decomposed into individual quanta that lead to single detection events. Our
main result is a bound on how sharply peaked in time these events can be, which
depends on the dimension of the signal generator. This result promises
applications in various directions, including information theory, quantum
clocks, and process simulation.
