Universal quantum frequency comb measurements by spectral mode-matching

The frequency comb of a multimode interferometer offers exceptional scalability potential for field-encoded quantum information. However, the staple field detection method, homodyne detection, cannot access quantum information in the whole comb because some spectral quadratures [and their asymmetries with respect to the local oscillator (LO)] are out of reach. We present here the first general approach to making optimal measurements of a multimode quantum optical source—something that is required for photonic quantum computing and is not possible when using homodyne detection with a pulse-shaped LO. This approach uses universal spectral mode-matching, which can be understood as interferometry with a memory effect. We derive a complete formalism and propose an implementation by microcavity arrays.