Donohue, J. M.Ansari, V.Řeháček, JaroslavHradil, ZdenekStoklasa, BohumilPaúr, MartinSánchez Soto, Luis LorenzoSilberhorn, C.2023-06-172023-06-172018-08-270031-900710.1103/PhysRevLett.121.090501https://hdl.handle.net/20.500.14352/12251We thank K. Bonsma-Fisher, O. DiMatteo, J. Gil-López, M. Allgaier, C. Fabre, N. Treps, and B. Brecht for fruitful discussions. This research has received funding from the European Unions (EU) Horizon 2020 research and innovation program under Grant Agreement No. 665148, the Grant Agency of the Czech Republic (Grant No. 18-04291S), Palacký University (Grant No. IGA-PrF-2018-003), and the Spanish MINECO (Grant No. FIS2015-67963-P). J. M. D. gratefully acknowledges support from Natural Sciences and Engineering Research Council of Canada.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 tenfold improvement in precision over the intensity-only Cramer-Rao bound.engjournal articlehttp://dx.doi.org/10.1103/PhysRevLett.121.090501https://journals.aps.orgopen access535Single-molecule microscopyFisher informationParameter-estimationOptical resolutionConversionInterferometryPowerÓptica (Física)2209.19 Óptica Física