RT Journal Article T1 Quantum-limited time-frequency estimation through mode-selective photon measurement A1 Donohue, J. M. A1 Ansari, V. A1 Řeháček, Jaroslav A1 Hradil, Zdenek A1 Stoklasa, Bohumil A1 Paúr, Martin A1 Sánchez Soto, Luis Lorenzo A1 Silberhorn, C. AB 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. PB American Physical Society SN 0031-9007 YR 2018 FD 2018-08-27 LK https://hdl.handle.net/20.500.14352/12251 UL https://hdl.handle.net/20.500.14352/12251 LA eng NO We 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. NO Unión Europea. H2020 NO Ministerio de Economía y Competitividad (MINECO) NO Grant Agency of the Czech Republic NO Palacky University DS Docta Complutense RD 11 jul 2025