On-demand generation of all four Bell states using a single PPKTP entangled photon source

Quantum Physics [Submitted on 21 Apr 2026] On-demand generation of all four Bell states using a single PPKTP entangled photon source Gayatri Thik, Amit Loyal, Srinivasan K, Raghavan G We present a compact, automated, high-brightness entangled photon source capable of generating all four Bell states with high fidelity. The system utilizes a type-0 quasi-phase-matched PPKTP crystal embedded within a polarization Sagnac interferometer. We introduce a switching scheme based on the controlled, motorized translation of the nonlinear crystal. This device is capable of generating any one of the Bell states on-demand. Experimentally, we demonstrate that translating the crystal from the interferometer's balanced position repeatedly toggles the state between |\phi^+ \rangle and |\phi^- \rangle (as well as |\psi^+ \rangle and |\psi^- \rangle) at regular intervals of 122 \pm 14 ~\mu m. Subsequently, a half-wave plate (HWP) in the idler arm transitions between the quantum states |\phi^{\pm}\rangle and |\psi^{\pm}\rangle. While the non-collinear geometry imposes an upper limit on the translation range as verified via EMCCD imaging, the source however, displays very little change of intensity in the operational window. State purity and entanglement are certified through quantum state tomography (QST), visibility measurements, Bell state measurements (BSM), and CHSH inequality violations, confirming that the source is robust and provides a repeatable, high-fidelity output. Comments: 11 pages, 13 figures, one table, Journal paper Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2604.19013 [quant-ph]   (or arXiv:2604.19013v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2604.19013 Focus to learn more Submission history From: Srinivasan K Dr [view email] [v1] Tue, 21 Apr 2026 03:04:23 UTC (25,980 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-04 References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)