Generation of polarization-entangled Bell states in monolithic photonic waveguides by leveraging intrinsic crystal properties
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| Format: | Preprint |
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2025
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| _version_ | 1866908423612792832 |
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| author | Vrckovnik, Trevor G. Arslan, Dennis Eilenberger, Falk Schmitt, Sebastian W. |
| author_facet | Vrckovnik, Trevor G. Arslan, Dennis Eilenberger, Falk Schmitt, Sebastian W. |
| contents | Advanced photonic quantum technologies -- from quantum key distribution to quantum computing -- require on-chip sources of entangled photons that are both efficient and readily scalable. In this theoretical study, we demonstrate the generation of polarization-entangled Bell states in structurally simple waveguides by exploiting the intrinsic properties of nonlinear crystals. We thereby circumvent elaborate phase-matching strategies that commonly involve the spatial modulation of a waveguide's linear or nonlinear optical properties. We derive general criteria for the second-order susceptibility tensor that enable the generation of cross-polarized photon pairs via spontaneous parametric down-conversion in single-material waveguides. Based on these criteria, we systematically categorize all birefringent, non-centrosymmetric crystal classes in terms of their suitability. Using coupled mode theory, we then numerically analyze cuboid waveguides made from two materials that are highly relevant to integrated photonics: lithium niobate, a well-established platform, and barium titanate, an emerging alternative. We find that barium titanate consistently outperforms lithium niobate by providing a higher nonlinear efficiency and high concurrence over a significantly broader spectral range. These findings outline a practical route toward highly efficient, fabrication-friendly, and scalable sources of polarization-entangled photons for integrated quantum photonic circuits. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_21228 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Generation of polarization-entangled Bell states in monolithic photonic waveguides by leveraging intrinsic crystal properties Vrckovnik, Trevor G. Arslan, Dennis Eilenberger, Falk Schmitt, Sebastian W. Optics Applied Physics Quantum Physics Advanced photonic quantum technologies -- from quantum key distribution to quantum computing -- require on-chip sources of entangled photons that are both efficient and readily scalable. In this theoretical study, we demonstrate the generation of polarization-entangled Bell states in structurally simple waveguides by exploiting the intrinsic properties of nonlinear crystals. We thereby circumvent elaborate phase-matching strategies that commonly involve the spatial modulation of a waveguide's linear or nonlinear optical properties. We derive general criteria for the second-order susceptibility tensor that enable the generation of cross-polarized photon pairs via spontaneous parametric down-conversion in single-material waveguides. Based on these criteria, we systematically categorize all birefringent, non-centrosymmetric crystal classes in terms of their suitability. Using coupled mode theory, we then numerically analyze cuboid waveguides made from two materials that are highly relevant to integrated photonics: lithium niobate, a well-established platform, and barium titanate, an emerging alternative. We find that barium titanate consistently outperforms lithium niobate by providing a higher nonlinear efficiency and high concurrence over a significantly broader spectral range. These findings outline a practical route toward highly efficient, fabrication-friendly, and scalable sources of polarization-entangled photons for integrated quantum photonic circuits. |
| title | Generation of polarization-entangled Bell states in monolithic photonic waveguides by leveraging intrinsic crystal properties |
| topic | Optics Applied Physics Quantum Physics |
| url | https://arxiv.org/abs/2506.21228 |