  Quantum anomaly manifests itself in the deviation of breathing mode frequency
from the scale invariant value of $2\omega$ in two-dimensional harmonically
trapped Fermi gases, where $\omega$ is the trapping frequency. Its recent
experimental observation with cold-atoms reveals an unexpected role played by
the effective range of interactions, which requires quantitative theoretical
understanding. Here we provide accurate, benchmark results on quantum anomaly
from a few-body perspective. We consider the breathing mode of a few trapped
interacting fermions in two dimensions up to six particles and present the mode
frequency as a function of scattering length for a wide range of effective
range. We show that the maximum quantum anomaly gradually reduces as effective
range increases while the maximum position shifts towards the weak-coupling
limit. We extrapolate our few-body results to the many-body limit and find a
good agreement with the experimental measurements. Our results may also be
directly applicable to a few-fermion system prepared in microtraps and optical
tweezers.
