Abstract
Quantum emitters promise to emit exactly one photon when pumped by a laser pulse. However, even in ideal systems, re-excitation during the laser pulse duration causes the consecutive emission of two photons, thus limiting the single-photon purity. Although the probability and characteristics of re-excitation are largely determined by the excitation scheme, until now, only resonant driving has been studied. Here, we demonstrate qualitative differences for phonon-assisted excitation and resolve the distinct temporal and spectral profile of each of the photons. These uncover correlations between the emission time and wavelength, resulting in an asymmetric two-photon spectrum. On a fundamental level, we show that this spectrum provides direct access to the Rabi frequency of an incoherently driven quantum dot. On the application side, we leverage the asymmetry to selectively suppress multiphoton noise, ensuring high single-photon purity regardless of the laser pulse length and thus enhancing implementations across quantum cryptography and quantum computing.
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Acknowledgements
The Authors would like to thank Paul Hagen for discussions regarding the phonon spectral density and Michal Vyvlecka for the early design of the QD excitation setup. L.J., L.M.H., P.I.S., T.W.S., M.B. and P.W. acknowledge funding from the European Union’s Horizon 2020 and Horizon Europe Research and Innovation programme under Grant Agreement and No. 899368 (EPIQUS), from the Marie Skłodowska-Curie Grant Agreement No. 956071 (AppQInfo). R.J., M.J., S.L.P. and P.M. greatly acknowledge the German Federal Ministry of Research, Technology and Space (BMFTR) via the Project QR.X (No.16KISQ013) and QR.N. (16KIS2207). Funding was also provided via the project EQSOTIC. (QuantERA II Programme that received funding from the EU’s H2020 research and innovation programme under the GA No 101017733, and respective BMFTR project number 16KIS2060K). The financial support by the Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development and the Christian Doppler Research Association is gratefully acknowledged. This research was funded in whole or in part by the Austrian Science Fund (FWF)[10.55776/F71]. For open access purposes, the author has applied a CC BY public copyright license to any author accepted manuscript version arising from this submission.
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Jehle, L., Hansen, L.M., Sund, P.I. et al. Asymmetric two-photon response of an incoherently driven quantum emitter. Nat Commun (2026). https://doi.org/10.1038/s41467-026-72706-z
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DOI: https://doi.org/10.1038/s41467-026-72706-z
