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arXiv:2610.23575

Noise suppression of quantum frequency conversion in thin-film lithium niobate waveguides via adapted poling

Ian Briggs, Pao-Kang Chen, Jiaqi Huang, Linran Fan

Published Oct 16, 2026• 0 citations
arXivHTMLPDF

Abstract

Quantum frequency conversion (QFC) enables optical interfaces between dissimilar quantum systems, but suppressing noise while maintaining high conversion efficiency remains challenging. Here, we demonstrate that adapted poling in thin-film lithium niobate (TFLN) waveguides reduces the pump-power requirement while shifting the dominant noise mechanism and its power scaling. In 2-cm-long waveguides, adapted poling enables maximum conversion efficiency at an on-chip pump power of $19\pm0.8$~mW, reducing the required pump power by 8~dB and the total conversion noise by 14~dB relative to conventional periodic poling at their respective maximum-conversion operating points. Controlled measurements with different pump conditions and device configurations reveal a transition from predominantly quadratic noise scaling in periodically poled devices to predominantly linear scaling in adapted-poling devices. This transition accompanies a shift from noise dominated by cascaded second-harmonic generation and Stokes spontaneous Raman scattering to direct anti-Stokes spontaneous Raman scattering. These results establish adapted poling as an effective approach to suppressing nonlinear noise, enabling low-noise integrated frequency converters for quantum networks.

DOI
10.48550/arxiv.2610.23575

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Quantum frequency conversion (QFC) enables optical interfaces between dissimilar quantum systems, but suppressing noise while maintaining high conversion efficiency remains challenging. Here, we demonstrate that adapted poling in thin-film lithium niobate (TFLN) waveguides reduces the pump-power requirement while shifting the dominant noise mechanism and its power scaling. In 2-cm-long waveguides, adapted poling enables maximum conversion efficiency at an on-chip pump power of 19±0.819\pm0.819±0.8mW, reducing the required pump power by 8dB and the total conversion noise by 14~dB relative to conventional periodic poling at their respective maximum-conversion operating points. Controlled measurements with different pump conditions and device configurations reveal a transition from predominantly quadratic noise scaling in periodically poled devices to predominantly linear scaling in adapted-poling devices. This transition accompanies a shift from noise dominated by cascaded second-harmonic generation and Stokes spontaneous Raman scattering to direct anti-Stokes spontaneous Raman scattering. These results establish adapted poling as an effective approach to suppressing nonlinear noise, enabling low-noise integrated frequency converters for quantum networks.
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We generate quantum-correlated photon pairs using cascaded χ ( 2 ) : χ ( 2 ) traveling-wave interactions for second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC) in a single periodically-poled thin-film lithium-niobate (TFLN) waveguide. When pulse-pumped at 50 MHz, a 4-mm-long poled region with nearly 300%/Wcm2 SHG peak efficiency yields a generated photon-pair probability of 7±0.2 × 10−4 with corresponding coincidence-to-accidental ratio (CAR) of 13.6±0.7. The CAR is found to be limited by Stokes/anti-Stokes Raman-scattering noise generated primarily in the waveguide. A Raman peak of photon counts at 250 cm−1 Stokes shift from the fundamental-pump wavenumber suggests most of the noise that limits the CAR originates within the lithium niobate material of the waveguide.
High-fidelity periodic poling of thin film lithium niobate (TFLN) waveguides is critical for robust, quasi-phase-matched three-wave mixing process such as second-harmonic generation and spontaneous parametric down conversion. Over the past decade, extensive research has been performed on design and fabrication of TFLN based optical waveguides, demonstrating high-performance electro-optic modulators, efficient wavelength converters and revealing their great potentials in heterogeneous integration with the conventional silicon photonic material platform. However, studies on poling of TFLN are still lacking, and uniformity of TFLN poling needs to be further improved, to achieve a comparable conversion efficiency as in its bulk counterparts. This dissertation discusses evaluation and optimization of TFLN poling, waveguide design, and device demonstration through characterization of efficient second-harmonic generation and high-quality entangled photon-pair generation. The results presented here indicate promising applications for robust and efficient TFLN devices in nonlinear and quantum optics in the telecommunications regime.
Quantum frequency conversion (QFC) is essential for bridging the spectral gap between stationary qubits and low-loss optical communication channels. Practicable QFC interfaces connecting ultraviolet and telecommunication bands are of great significance but have remained elusive, constrained by the dual challenges of a high-performance frequency converter and effective noise suppression in short-wavelength pumping configurations. We address this by demonstrating the phase-matching mechanism with domain defects and differential-tuning behavior of the spontaneous parametric down-conversion noises. Based on a quantitative analysis of performance degradation induced by domain defects, we propose specific fabrication guidelines and experimentally achieve an ultrahigh normalized conversion efficiency of 839%/(W cm^{2}) for the fundamental guided mode in thin-film lithium niobate waveguides. Meanwhile, we reveal a new noise control mechanism for short-wavelength pumping by utilizing the differential-tuning behaviors of difference-frequency generation and spontaneous parametric down-conversion processes. Then a single-stage QFC from 393 nm to the telecom C band with a record-high external efficiency of 28.8% and an ultralow noise level of 35 counts per second is achieved experimentally. The proposed mechanisms would enable other QFCs with higher efficiency and lower noise, advancing the development of scalable quantum networks. Furthermore, it holds significant potential for driving progress in both classical and integrated nonlinear photonics.
Thanks to its high quadratic nonlinear susceptibilty and low propagation losses, thin film lithium niobate (TFLN) on insulator is an ideal platform for laser frequency conversion and generation of quantum states of light. Frequency conversion is usually achieved by quasi-phase matching (QPM) via electric-field poling. However, this scheme shows very high sensitivity to the dimensions of the waveguide, poling period and duty cycle, resulting in a lack of repeatability of the phase matched wavelength and efficiency, which in turn limits the spread of TFLN frequency converters in complex circuits and hinders wafer-scale production. Here we propose a layer-poled modal phase matching (MPM) that is 5 to 10 times more robust towards fabrication uncertainties and theoretically more efficient than conventional QPM. By selectively poling the bottom part of the waveguide all along its length, second harmonic is efficiently generated on a higher order waveguide's mode. We validate this approach by poling TFLN waveguides as a post-process after the fabrication in a foundry process. We perform a tolerance analysis and compare the experimental results with conventional QPM second harmonic generation process on the same waveguides. Then, we show how MPM can be exploited to obtain efficient intraband frequency conversion processes at telecom wavelengths by leveraging simultaneous second harmonic and difference frequency generation in the same waveguide.