Quantum processes which do not use coherence

Understand

A major signature of quantum mechanics beyond classical physics is coherence, the existence of superposition states.

• The recently developed resource theory of quantum coherence allows the formalisation of incoherent operations -- those operations which cannot create coherence.
• We identify the set of operations which additionally do not use coherence.
• These are such that coherence cannot be exploited by a classical observer, who measures incoherent properties of the system, to go beyond classical dynamics.