  Quantum gravity remains an elusive theory, in spite of our thorough
understanding of the quantum theory and the general theory of relativity
separately, presumably due to the lack of any observational clues. We argue
that the theory of quantum gravity has a strong constraining anchor in the
sector of gravitational radiation ensuring reliable physical clues, albeit in a
limited observable form. In particular, all types of gravitational waves
expected to be observable in LIGO-like advanced detectors are fully quantum
mechanical states of radiation. Exact equivalence of the full quantum gravity
theory with the familiar semiclassical theory is ensured in the radiation
sector, in most real situations where the relevant quantum operator functions
are normal ordered, by the analogue of the optical equivalence theorem in
quantum optics. We show that this is indeed the case for detection of the waves
from a massive binary system, a single gravitational atom, that emits coherent
radiation. The idea of quantum-gravitational optics can assist in guiding along
the fuzzy roads to quantum gravity.
