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arXiv:2510.03620 · Advanced Quantum Technologies

Compact Non‐Degenerate Entangled‐Photon Source and Near‐Infrared‐To‐Telecom Quantum Teleportation

Xu‐Jie Peng, Ling‐Xuan Kong, He Lu

Published Sep 25, 2025• 0 citations
arXivHTMLPDF

Abstract

Abstract The polarization‐entangled photon source (PEPS) at non‐degenerated wavelengths is pivotal to connect quantum systems working at different wavelengths, with the assistance of quantum teleportation. Here, a compact Sagnac‐type photon source is designed and demonstrated, in which two photons with wavelengths at 810 and 1550 nm are highly entangled in polarization degree of freedom. The two photons are generated from a periodically poled lithium niobate crystal pumped with a 532 nm continuous‐wave laser, via type‐0 nondegenerate spontaneous parametric down‐conversion. The polarization of three lights is rotated by a single periscope, which makes the Sagnac interferometer compact and stable. The generated two photons are with high brightness of pairs/s/mW, which are highly entangled with fidelity of . The entanglement is verified by violating the Clauser‐Horne‐Shimony‐Holt inequality with . Finally, teleportation is demonstrated with this nondegenerate source, in which photonic states at 810 nm is teleported to 1550 nm with fidelity of .

DOI
10.1002/qute.202500574

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Abstract The polarization‐entangled photon source (PEPS) at non‐degenerated wavelengths is pivotal to connect quantum systems working at different wavelengths, with the assistance of quantum teleportation. Here, a compact Sagnac‐type photon source is designed and demonstrated, in which two photons with wavelengths at 810 and 1550 nm are highly entangled in polarization degree of freedom. The two photons are generated from a periodically poled lithium niobate crystal pumped with a 532 nm continuous‐wave laser, via type‐0 nondegenerate spontaneous parametric down‐conversion. The polarization of three lights is rotated by a single periscope, which makes the Sagnac interferometer compact and stable. The generated two photons are with high brightness of pairs/s/mW, which are highly entangled with fidelity of . The entanglement is verified by violating the Clauser‐Horne‐Shimony‐Holt inequality with . Finally, teleportation is demonstrated with this nondegenerate source, in which photonic states at 810 nm is teleported to 1550 nm with fidelity of .
Sources of entangled photon pairs are a key component in both fundamental tests of quantum theory and practical applications such as quantum key distribution and quantum computing. In this work, we describe and characterize a source of polarization entangled photon pairs based on two spontaneous parametric down-conversion crystals in a Sagnac interferometer. Our source is compact and produces high-quality entangled states in a very flexible manner. The wavelengths of the photon pairs (around 810 and 1550 nm), the phase between orthogonal components of the entangled state, and the tangle of the state are all independently adjustable. In addition to presenting basic characterization data, we present experimental violations of Clauser-Horne-Shimony-Holt and Leggett inequalities, as well as an instance of the ``beautiful'' Bell inequality, which has not previously been tested experimentally.
Combining a Ti-diffusion periodically poled lithium niobate (PPLN) waveguide with a Sagnac interferometer, two opposite directions type-II spontaneous parametric down conversions (SPDC) occur coherently and yield a high brightness, high stability polarization entanglement source. The source produces degenerate photon pairs at 1540.4 nm with a brightness of B = (1.36 ± 0.03) × 106 pairs/(s⋅nm⋅mW). We perform quantum state tomography to reconstruct the density matrix of the output state and obtain a fidelity of F = 0.983 ± 0.001. The high brightness and phase stability of our waveguide source enable a wide range of quantum information experiments operating at a low pump power as well as hold the advantage in mass production which can promote the practical applications of quantum technologies.
We demonstrate a compact, practical all-fiber source of non-degenerate telecom-band polarization-entangled photon pairs assembled from off-the-shelf components. The compact fiber-integrated architecture is designed to be affordable, straightforward to assemble and align, and compatible with existing optical-fiber infrastructure. Photon pairs are generated through type-0 spontaneous parametric down-conversion in a pigtailed periodically poled lithium-niobate waveguide embedded in a Sagnac interferometer. At 0.5 mW pump power, quantum-state tomography yields a Bell-state fidelity FΦ−=0.850F_{Φ^-}=0.850FΦ−​=0.850, purity P=0.836P=0.836P=0.836, and concurrence C=0.782C=0.782C=0.782. A separate CHSH measurement gives S=2.3301±0.0075S=2.3301\pm0.0075S=2.3301±0.0075. The measured Bell-state fidelity is sufficient for the reconstructed polarization state to support qubit teleportation above the classical fidelity limit under ideal protocol operations. Analysis of the density matrix shows that approximately 96.7% of the population remains in the desired ∣HH⟩|HH\rangle∣HH⟩-∣VV⟩|VV\rangle∣VV⟩ subspace, with a normalized coherence of approximately 0.86. A residual relative-phase offset indicates that local phase compensation could increase the Bell-state fidelity to approximately 0.8865. We further characterize the brightness--quality trade-off and obtain a corrected pair-rate slope of (0.918±0.040)(0.918\pm0.040)(0.918±0.040) Mcps mW−1^{-1}−1. The broadband emission and fiber interfaces offer a route to multiuser entanglement distribution through off-the-shelf multichannel wavelength-division multiplexers with passbands matched to the signal and idler wavelengths.
We report a Sagnac-type source based on a MgO:PPLN non-linear crystal pumped with a 532 nm continuous-wave laser, which generates spectrally non-degenerate, polarization-entangled photon pairs of 785 nm signal and 1651 nm idler wavelength, via the type-0 spontaneous parametric downconversion (SPDC) process. We use standard off-the-shelf components; hence, no custom-designed multi-wavelength polarization optics are required. At the same time, long-term phase stability can be achieved due to the geometry of our Sagnac-type design. The source's brightness is 6.17(4)×106 pairs/sec/mW, which is comparable to the brightest state-of-the-art non-degenerate polarization-entangled photon-pair source. The spectral bandwidth of the single photon is approximately 195 GHz (root mean square). The fidelity of the entangled state is measured to be 96.72(1)%, the concurrence is 94.7(2)%, and the Bell-CHSH value S=2.71(6). This source has the potential to be applied in long-distance quantum communication using both free-space and fiber links simultaneously.
We report a source of polarization-entangled photon pairs in the 1550-nm telecommunication band, which is based on non-collinear spontaneous parametric down-conversion in a periodically poled lithium niobate crystal pumped by picosecond pulses. This source is realized utilizing a polarization-based Sagnac interferometer employing a type-0 non-collinear quasi-phase-matching configuration. Polarization entanglement is verified through measurement of the polarization-correlation interference fringes with visibility >96% and by testing the experimental violation of the Clauser-Horne-Shimony-Holt (CHSH) form of Bell's inequality. The CHSH-Bell parameter S is found to be 2.72 ± 0.04, with 18 standard deviations from the statistical uncertainty.
This study presents an ultrabright polarization‐entangled photon source that is optimally coupled into single‐mode fibers (SMFs). This study theoretically and experimentally examines the characteristics of spontaneous parametric down‐conversion (SPDC) photons, including their spectrum, bandwidth, emission angle, and intensity, as functions of crystal length, temperature and beam waist condition. Notably, this study measures the collinear spatial modes of photon‐pairs and collection optics under various beam waist conditions and analyzes them using a collinear Gaussian approximation model. By employing a simple mode‐matching optical setup, it optimizes the SMF coupling and heralding efficiencies of the photon‐pairs. Consequently, it achieves a spectral brightness exceeding 2.0 MHz mW −1 nm −1 from a fiber‐coupled entangled photon source, utilizing a 30 mm ppKTP crystal inside a polarization Sagnac interferometer. This represents the highest spectral brightness of SPDC photons generated using a continuous‐wave (CW) laser pumped bulk crystal to date. Polarization entanglement is verified by a quantum state tomography and a polarization‐correlation measurement. The fidelity of the entangled state is measured to be 97.8% and the Bell‐Clauser‐Horne‐Shimony‐Holt value S = 2.782 ± 0.04. The results obtained here provide practical insights for designing high‐performance SPDC sources for satellite‐based communication and long‐distance optical links with extremely high‐photon loss.