Counter-Propagating SPDC Photon Pair Generation with High Coincidence-to-Accidental Ratio

Tim Julian Wörmann, Rodrigo Amorim, Andrius Žukauskas, Lars Grüner-Nielsen, Valdas Pašiškevičius, Karsten K. Rottwitt

Published Jan 1, 2026• 1 citation

Abstract

We demonstrate counter-propagating spontaneous parametric down-conversion in a sub-micron periodically poled Rb-doped KTP crystal, matching the highest reported coincidence-to-accidental ratio. A first heralded g H (2) measurement confirms the high-purity single-photon generation.

DOI: 10.1364/cleo_fs.2026.ftu1d.5

Related papers

Ultra-low-noise heralded single photons from counter-propagating SPDC

Rodrigo Amorim, Tim Julian Wörmann, Andrius Žukauskas +3 more

Over the past decade, counter-propagating spontaneous parametric down-conversion (CPSPDC) has attracted interest due to its ability to generate narrowband and spectrally pure photon pairs without the need for strong spectral filtering. While prior work has established the spectral characteristics of CPSPDC, its performance as a heralded single-photon source (HSPS) remains limited. Here, we present a detailed HSPS characterization of a first-order quasi-phase-matched CPSPDC source based on a sub-μm periodically poled potassium titanyl phosphate crystal. We measure an internal pair-generation rate of 1.3×10 3 pairs/s/mW under CW pumping, in addition to a high coincidence-to-accidental ratio exceeding 1.4×10 5 , and furthermore obtain the lowest heralded second-order correlation value of (8.57±4.95)×10 -6 ever reported. We also show a Hong–Ou–Mandel interference experiment that yields a raw visibility of 70±1%, confirming photon indistinguishability. These results demonstrate CPSPDC as a strong candidate for generating high-quality single photons for quantum information processing and long-distance quantum communication applications.

Optica QuantumJul 28, 20260 citations

Counter-directional generation of photon-pairs in periodically poled Rb-KTiOPO4

Marcin Świłło, Patrick Mutter, Albert Peralta Amores +2 more

For the first time, we show spectral and polarization indistinguishability of photon pairs generated in counter-propagating degenerate spontaneous parametric downconversion in the telecommunications band using first-order quasi-phase-matching in periodically poled Rb-KTiOPO4.

Jan 1, 20240 citations

Higher-Order Spontaneous Parametric Down-Conversion With Back-Propagating Idler Using Submicron Poled KTP

Mark Bashkansky, I. Vurgaftman, John F. Reintjes

We demonstrate Spontaneous Parametric Down-Conversion in one-dimensional periodically poled KTP waveguide with counter-propagating signal and idler beams. This is accomplished by using sub-micron poling and higher-order quasi-phase-matching interactions.

Frontiers in OpticsJan 1, 20150 citations

Counter-propagating spectrally uncorrelated biphotons at 1550 nm generated from periodically poled MTiOXO4 (M = K, Rb, Cs; X = P, As)

Wu‐Hao Cai, Bei Wei, Shun Wang +1 more

We theoretically investigated spectrally uncorrelated biphotons generated in a counter-propagating spontaneous parametric downconversion (CP-SPDC) from periodically poled M T i O X O 4 ( M = K , Rb, Cs; X = P , As) crystals. By numerical calculation, it was found that the five crystals from the KTP family can be used to generate heralded single photons with high spectral purity and wide tunability. Under the type-0 phase-matching condition, the purity at 1550 nm was between 0.91 and 0.92, and the purity can be maintained over 0.90 from 1500 nm to 2000 nm wavelength. Under the type-II phase-matching condition, the purity at 1550 nm was 0.96, 0.97, 0.97, 0.98, and 0.98 for PPKTP, PPRTP, PPKTA, PPRTA, and PPCTA, respectively; furthermore, the purity can be kept over 0.96 for more than 600 nm wavelength range. We also simulated the Hong–Ou–Mandel interference between independent photon sources for PPRTP crystals at 1550 nm, and interference visibility was 92% (97%) under the type-0 (type-II) phase-matching condition. This study may provide spectrally pure narrowband single-photon sources for quantum memories and quantum networks at telecom wavelengths.

arXiv:2009.13321Journal of the Optical Society of America BAug 19, 202010 citations

Backward-wave spontaneous parametric down-conversion in a periodically poled KTP waveguide

Латыпов Ильнур Зиннурович, Anatoly Shukhin, D O Akat’ev +2 more

Backward-wave spontaneous parametric down-conversion in a periodically poled potassium titanyl phosphate (KTP) crystal has been experimentally observed for the first time. The correlation and spectral characteristics of the generated single-photon states are investigated.

Quantum ElectronicsSep 1, 201710 citations

Observation of frequency-uncorrelated photon pairs generated by counter-propagating spontaneous parametric down-conversion

Yichen Liu, Dongjie Guo, Kun-Qian Ren +9 more

We report the generation of frequency-uncorrelated photon pairs from counter-propagating spontaneous parametric down-conversion in a periodically-poled KTP waveguide. The joint spectral intensity of photon pairs is characterized by measuring the corresponding stimulated process, namely, the difference frequency generation process. The experimental result shows a clear uncorrelated joint spectrum, where the backward-propagating photon has a narrow bandwidth of 7.46 GHz and the forward-propagating one has a bandwidth of 0.23 THz like the pump light. The heralded single-photon purity estimated through Schmidt decomposition is as high as 0.996, showing a perspective for ultra-purity and narrow-band single-photon generation. Such unique feature results from the backward-wave quasi-phase-matching condition and does not has a strict limitation on the material and working wavelength, thus fascinating its application in photonic quantum technologies.

Scientific ReportsJun 16, 202132 citations