The attowatt measures extremely faint power levels, representing 10⁻¹⁸ watts. It is encountered in radio astronomy, quantum optics, and deep-space communications where receivers must detect signals that have degraded over vast distances. Thermal noise at room temperature often dwarfs signals at this level, requiring cryogenic cooling to measure.
Heard on the job
The receiver sensitivity bottoms out at around five attowatts before the signal is lost in the noise floor.