  The wave-particle duality of light introduces two fundamental problems to
imaging, namely, the diffraction limit and the photon shot noise. Quantum
information theory can tackle them both in one holistic formalism: model the
light as a quantum object, consider any quantum measurement, and pick the one
that gives the best statistics. While Helstrom pioneered the theory half a
century ago and first applied it to incoherent imaging, it was not until
recently that the approach offered a genuine surprise on the age-old topic by
predicting a new class of superior imaging methods. For the resolution of two
sub-Rayleigh sources, the new methods have been shown theoretically and
experimentally to outperform direct imaging and approach the true quantum
limits. Recent efforts to generalize the theory for an arbitrary number of
sources suggest that, despite the existence of harsh quantum limits, the
quantum-inspired methods can still offer significant improvements over direct
imaging for subdiffraction objects, potentially benefiting many applications in
astronomy as well as fluorescence microscopy.
