  A recent approach [Bohmann and Agudelo, Phys. Rev. Lett. 124, 133601 (2020)]
allows for the discriminating and noise-tolerant detection of non-classical
behaviour of quantum states. But it does not provide a sensitive measure for
the quantumness of states; to date no such measure is known. We amend Bohmann
and Agudelo's approach such that it inherits the multiple strengths of the
original proposal whilst providing a quantumness measure, {\Xi}. {\Xi} is
discriminating, exquisitely sensitive and grows monotonically with an increase
in the system's non-classical excitations.
