Quantum-limited optical delay sensing across an enhanced dynamic range by frequency-resolving two-photon interference

Abstract: Hong-Ou-Mandel interferometry is an effective tool for precision sensing, but it faces a fundamental trade-off between dynamic range and measurement precision. To overcome this limitation, we sample the frequencies of two interfering photons, which extends the sensitivity in the time domain. This enhances the dynamic range of optical delay estimation by up to twenty times compared to the non-resolved estimates. We demonstrate this approach with independent photon sources and show the precision scaling with the detector frequency resolution. This technique enables scan-free nanometre resolution depth sensing over a millimetre-scale range, with applications in biological and nanomaterial imaging.