  Due to conservation of energy we cannot directly turn a quantum system with a
definite energy into a superposition of different energies. However, if we have
access to an additional resource in terms of a system with a high degree of
coherence, as for standard models of laser light, we can overcome this
limitation. The question is to what extent coherence gets degraded when
utilized. Here it is shown that coherence can be turned into a catalyst,
meaning that we can use it repeatedly without ever diminishing its power to
enable coherent operations. This finding stands in contrast to the degradation
of other quantum resources, and has direct consequences for quantum
thermodynamics, as it shows that latent energy that may be locked into
superpositions of energy eigenstates can be released catalytically.
