Autonomous quantum machines and the finite sized Quasi-Ideal clock

Understand

Processes such as quantum computation, or the evolution of quantum cellular automata are typically described by a unitary operation implemented by an external observer.

• In particular, an interaction is generally turned on for a precise amount of time, using a classical clock.
• A fully quantum mechanical description of such a device would include a quantum description of the clock whose state is generally disturbed because of the back-reaction on it.
• Such a description is needed if we wish to consider finite sized autonomous quantum machines requiring no external control.