No, a sonic boom does not occur when a plane slows down from supersonic speed (faster than the speed of sound) to subsonic speed (slower than the speed of sound). The sonic boom is a phenomenon that happens when an aircraft is traveling at or above the speed of sound.
A sonic boom is created by the shock waves generated by an aircraft as it moves through the air faster than the speed of sound. These shock waves propagate outward in a cone shape from the aircraft, and when they reach the ground or an observer, they are heard as a loud, explosive sound.
When an aircraft decelerates from supersonic to subsonic speed, the shock waves are no longer being generated because the aircraft is not traveling faster than the speed of sound. As a result, there is no additional sonic boom produced during the deceleration process.
It's important to note that even during the deceleration process, there may be other types of noise associated with the aircraft, such as engine noise or airflow disturbances, but these are distinct from the sonic boom created when the aircraft is supersonic.