  By projecting onto complex optical mode profiles, it is possible to estimate
arbitrarily small separations between objects with quantum-limited precision,
free of uncertainty arising from overlapping intensity profiles. Here we extend
these techniques to the time-frequency domain using mode-selective
sum-frequency generation with shaped ultrafast pulses. We experimentally
resolve temporal and spectral separations between incoherent mixtures of
single-photon level signals ten times smaller than their optical bandwidths
with a ten-fold improvement in precision over the intensity-only Cram\'er-Rao
bound.

Quantum Physics;Optics