  Advancing our understanding of non-trivial quantum effects in biomolecular
complexes operating in physiological conditions requires the precise
characterisation of the non-classicalities that may be present in such systems
as well as asserting whether such features are required for robust function.
Here we consider an avian-inspired quantum magnetic sensor composed of two
radicals with a third "scavenger" radical under the influence of a collisional
environment that allows to capture a variety of decoherence processes. We show
that basis-independent coherence, in which the initial system-environment state
is non-maximally mixed, is necessary for optimal performance of the quantum
magnetic sensor, and appears to be sufficient in particular situations. We
discuss how such non-maximally mixed initial states may be common for a variety
of biomolecular scenarios. Our results therefore suggest that a small degree of
coherence--regardless of basis--is likely to be a quantum resource for
biomolecular systems operating at the interface between the quantum and
classical domains.
