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Q: Fachverband Quantenoptik und Photonik
Q 60: Quantum Communication, Networks, Repeaters, & QKD II
Q 60.4: Talk
Thursday, March 5, 2026, 15:30–15:45, P 10
The influence of back-decays on the indistinguishability of single Raman photons — •Pascal Baumgart, Max Bergerhoff, Jonas Meiers, Stephan Kucera, and Jürgen Eschner — Universität des Saarlandes, Experimentalphysik, 66123 Saarbrücken, Germany
The ability to generate indistinguishable single photons capable of high-contrast Hong-Ou-Mandel (HOM) interference is the keystone for implementing entanglement swapping protocols based on photonic Bell state measurements, which may be used to realise quantum repeater schemes [1] or connect quantum processing units in distributed quantum computing [2].
One method to generate single photons is laser excitation
of a Raman transition with a stable ground state and a short-lived
excited state that decays to a third meta-stable state under the emission of a Raman photon. However, the indistinguishability of these photons is
influenced by the possibility of back-decay to the ground state and subsequent re-excitation on the driven transition, which broadens the photonic temporal wave packet beyond the Fourier limit [3]. We investigate this behavior for trapped 40Ca+ ions using few-nanosecond excitation pulses. Numerical simulations identify the mean number of back-decays as a measurable quantity that correlates with achievable HOM visibility. This is supported by experimental data.
[1] P. van Loock et al., Adv. Quantum Technol. 3, 1900141 (2020)
[2] J. O’Reilly et al., Phys. Rev. Lett. 133, 090802 (2024)
[3] P. Müller et al., Phys. Rev. A 96, 023861 (2017)
Keywords: Trapped ions; Atom-photon entanglement; Hong-Ou-Mandel interference; Bell measurement; Atom-atom entanglement