title: Mode engineering for realistic quantum-enhanced interferometry.
abstract: Quantum metrology overcomes standard precision limits by exploiting collective quantum superpositions of physical systems used for sensing, with the prominent example of non-classical multiphoton states improving interferometric techniques. Practical quantum-enhanced interferometry is, however, vulnerable to imperfections such as partial distinguishability of interfering photons. Here we introduce a method where appropriate design of the modal structure of input photons can alleviate deleterious effects caused by another, experimentally inaccessible degree of freedom. This result is accompanied by a laboratory demonstration that a suitable choice of spatial modes combined with position-resolved coincidence detection restores entanglement-enhanced precision in the full operating range of a realistic two-photon Mach-Zehnder interferometer, specifically around a point which otherwise does not even attain the shot-noise limit due to the presence of residual distinguishing information in the spectral degree of freedom. Our method highlights the potential of engineering multimode physical systems in metrologic applications.
authors.affiliation: Faculty of Physics, University of Warsaw, Pasteura 5, Warsaw, 02-093, Poland.
authors.forename: Michał
authors.initials: M
authors.lastname: Jachura
authors.affiliation: Faculty of Physics, University of Warsaw, Pasteura 5, Warsaw, 02-093, Poland. radekch@fuw.edu.pl.
authors.forename: Radosław
authors.initials: R
authors.lastname: Chrapkiewicz
authors.affiliation: Faculty of Physics, University of Warsaw, Pasteura 5, Warsaw, 02-093, Poland.
authors.forename: Rafał
authors.initials: R
authors.lastname: Demkowicz-Dobrzański
authors.affiliation: Faculty of Physics, University of Warsaw, Pasteura 5, Warsaw, 02-093, Poland.
authors.forename: Wojciech
authors.initials: W
authors.lastname: Wasilewski
authors.affiliation: Faculty of Physics, University of Warsaw, Pasteura 5, Warsaw, 02-093, Poland.
authors.forename: Konrad
authors.identifier: http://orcid.org/0000-0002-5389-6897
authors.initials: K
authors.lastname: Banaszek