{"title":"Pulse characterization at the single-photon level through chronocyclic <i>Q</i>-function measurements","user_id":"27150","publisher":"Optica Publishing Group","article_number":"5551","abstract":[{"lang":"eng","text":"<jats:p>The characterization of the complex spectral amplitude, that is, the spectrum and spectral phase, of single-photon-level light fields is a crucial capability for modern photonic quantum technologies. Since established pulse characterization techniques are not applicable at low intensities, alternative approaches are required. Here, we demonstrate the retrieval of the complex spectral amplitude of single-photon-level light pulses through measuring their chronocyclic <jats:italic toggle=\"yes\">Q</jats:italic> −function. Our approach draws inspiration from quantum state tomography by exploiting the analogy between quadrature phase space and time-frequency phase space. In the experiment, we perform time-frequency projections with a quantum pulse gate (QPG), which directly yield the chronocyclic <jats:italic toggle=\"yes\">Q</jats:italic> −function. We evaluate the complex spectral amplitude from the measured chronocyclic <jats:italic toggle=\"yes\">Q</jats:italic> −function data with maximum likelihood estimation (MLE), which is the established technique for quantum state tomography. The MLE yields not only an unambigious estimate of the complex spectral amplitude of the state under test that does not require any <jats:italic toggle=\"yes\">a priori</jats:italic> information, but also allows for, in principle, estimating the spectral-temporal coherence properties of the state. Our method accurately recovers features such as jumps in the spectral phase and is resistant against regions with zero spectral intensity, which makes it immediately beneficial for classical pulse characterization problems.</jats:p>"}],"publication_status":"published","publication_identifier":{"issn":["1094-4087"]},"intvolume":"        33","date_updated":"2025-12-18T16:08:40Z","year":"2024","citation":{"mla":"Bhattacharjee, Abhinandan, et al. “Pulse Characterization at the Single-Photon Level through Chronocyclic <i>Q</i>-Function Measurements.” <i>Optics Express</i>, vol. 33, no. 3, 5551, Optica Publishing Group, 2024, doi:<a href=\"https://doi.org/10.1364/oe.540125\">10.1364/oe.540125</a>.","ieee":"A. Bhattacharjee <i>et al.</i>, “Pulse characterization at the single-photon level through chronocyclic <i>Q</i>-function measurements,” <i>Optics Express</i>, vol. 33, no. 3, Art. no. 5551, 2024, doi: <a href=\"https://doi.org/10.1364/oe.540125\">10.1364/oe.540125</a>.","bibtex":"@article{Bhattacharjee_Folge_Serino_Řeháček_Hradil_Silberhorn_Brecht_2024, title={Pulse characterization at the single-photon level through chronocyclic <i>Q</i>-function measurements}, volume={33}, DOI={<a href=\"https://doi.org/10.1364/oe.540125\">10.1364/oe.540125</a>}, number={35551}, journal={Optics Express}, publisher={Optica Publishing Group}, author={Bhattacharjee, Abhinandan and Folge, Patrick Fabian and Serino, Laura Maria and Řeháček, Jaroslav and Hradil, Zdeněk and Silberhorn, Christine and Brecht, Benjamin}, year={2024} }","ama":"Bhattacharjee A, Folge PF, Serino LM, et al. Pulse characterization at the single-photon level through chronocyclic <i>Q</i>-function measurements. <i>Optics Express</i>. 2024;33(3). doi:<a href=\"https://doi.org/10.1364/oe.540125\">10.1364/oe.540125</a>","short":"A. Bhattacharjee, P.F. Folge, L.M. Serino, J. Řeháček, Z. Hradil, C. Silberhorn, B. Brecht, Optics Express 33 (2024).","apa":"Bhattacharjee, A., Folge, P. F., Serino, L. M., Řeháček, J., Hradil, Z., Silberhorn, C., &#38; Brecht, B. (2024). Pulse characterization at the single-photon level through chronocyclic <i>Q</i>-function measurements. <i>Optics Express</i>, <i>33</i>(3), Article 5551. <a href=\"https://doi.org/10.1364/oe.540125\">https://doi.org/10.1364/oe.540125</a>","chicago":"Bhattacharjee, Abhinandan, Patrick Fabian Folge, Laura Maria Serino, Jaroslav Řeháček, Zdeněk Hradil, Christine Silberhorn, and Benjamin Brecht. “Pulse Characterization at the Single-Photon Level through Chronocyclic <i>Q</i>-Function Measurements.” <i>Optics Express</i> 33, no. 3 (2024). <a href=\"https://doi.org/10.1364/oe.540125\">https://doi.org/10.1364/oe.540125</a>."},"_id":"63216","publication":"Optics Express","issue":"3","language":[{"iso":"eng"}],"doi":"10.1364/oe.540125","department":[{"_id":"15"},{"_id":"623"}],"status":"public","author":[{"first_name":"Abhinandan","id":"95902","last_name":"Bhattacharjee","full_name":"Bhattacharjee, Abhinandan"},{"id":"88605","first_name":"Patrick Fabian","last_name":"Folge","full_name":"Folge, Patrick Fabian"},{"id":"88242","first_name":"Laura Maria","last_name":"Serino","full_name":"Serino, Laura Maria"},{"first_name":"Jaroslav","full_name":"Řeháček, Jaroslav","last_name":"Řeháček"},{"first_name":"Zdeněk","last_name":"Hradil","full_name":"Hradil, Zdeněk"},{"id":"26263","first_name":"Christine","last_name":"Silberhorn","full_name":"Silberhorn, Christine"},{"full_name":"Brecht, Benjamin","orcid":"0000-0003-4140-0556 ","last_name":"Brecht","first_name":"Benjamin","id":"27150"}],"type":"journal_article","volume":33,"date_created":"2025-12-18T16:08:16Z"}