Atomic Biphotons Demonstrate OAM-to-Polarization Mapping with 99% Fidelity and Clauser-Horne-Shimony-Holt Parameter of 2.7
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The creation of robustly entangled photons is central to advances in quantum communication and computation, but generating entanglement in specific properties remains a significant challenge. Chang-Wei Lin, Yi-Ting Ma, and Jiun-Shiuan Shiu, alongside Yong-Fan Chen and colleagues at National Cheng Kung University, Taiwan, now demonstrate a method for creating polarization-entangled photons using a cold-atom system.
The team overcomes inherent limitations that typically favour entanglement based on orbital angular momentum, instead coherently mapping this property onto photon polarization. This achievement not only generates high-fidelity polarization entanglement, confirmed through detailed measurements of Bell states and nonlocal correlations, but also establishes a crucial interface for integrating atomic resources with existing polarization-based quantum networks, representing a substantial step towards practical quantum technologies. Orbital angular momentum (OAM) entanglement represents a valuable resource for high-dimensional quantum communication, but accessing and manipulating this entanglement can be challenging. Researchers coherently map a selected two-dimensional OAM subspace onto the polarization basis, effectively opening a previously inaccessible polarization channel for quantum information processing. Quantum-state tomography confirms that this mapping preserves the crucial biphoton coherence necessary for entanglement. The four polarization Bell states are generated with high fidelity, achieving values of 92 to 94 percent with statistical uncertainties of only a few percent, and a Clauser, Horne, Shimony, Holt parameter of 2. 44 verifies the survival of nonlocal correlations throughout the transfer process. This work demonstrates, to the best of the researchers’ knowledge, the first successful OAM-to-polarization entanglement transfer in a cold-atom spontaneous four-wave mixing platform.
Cold Atom Entanglement, Tomography and Error Analysis This document provides a comprehensive explanation of the experimental setup, data analysis, and error estimation for a quantum entanglement experiment using cold atoms. It thoroughly covers all aspects, from the theoretical basis of tomography to the practical details of error analysis, which is crucial for reproducibility and understanding the experiment’s limitations. The explanations are generally well-written and easy to follow, even for those with a solid background in quantum optics. The document demonstrates a strong understanding of the underlying theory through the inclusion of equations for density matrix reconstruction, cost functions, and error estimation. The detailed error analysis, employing a Monte Carlo method, is a robust approach, and the explanation of how the low duty cycle affects the uncertainties is particularly important. The authors transparently acknowledge the limitations of their setup and explain how it impacts the results. Adding a few diagrams, such as a schematic of the experimental setup, a diagram illustrating the temporal waveform and coincidence counting process, and a visual representation of the Monte Carlo simulation, would significantly enhance understanding. Ensuring consistent notation throughout, such as using ˆρ or ρ consistently for the density matrix, would also improve readability. Expanding slightly on why the low duty cycle specifically impacts the statistical uncertainty, and providing a more detailed explanation of the accidental background and how it’s subtracted, would be helpful. Briefly defining acronyms the first time they appear would also make the document more accessible. Considering a more consistent formatting style for equations and lists, and adding cross-references to concepts explained elsewhere, would further enhance the document. Overall, this is an exceptionally well-written and thorough supplemental material document that serves as a model for how such material should be presented in scientific publications.
Polarization Entanglement From Cold Atomic Systems Scientists have demonstrated the generation of polarization-entangled biphotons using a cold-atom system, overcoming limitations that typically favour orbital angular momentum (OAM) entanglement instead. This breakthrough involved coherently mapping a selected two-dimensional OAM subspace onto the polarization basis, effectively opening a previously inaccessible polarization channel for entanglement.
The team implemented this process using a magneto-optical trap to prepare an ensemble of 87Rb atoms, driven by counter-propagating laser fields to generate the entangled photon pairs through spontaneous four-wave mixing. Experiments revealed a biphoton generation rate of 5×10 6 s -1 , achieved with an optical depth of 48 ±2 within the atomic ensemble. The researchers utilized spatial light modulators, programmed with computer-generated fork holograms, to precisely control the OAM of the photons and transfer the entanglement to their polarization state. Quantum state tomography confirmed that this mapping preserves the coherence of the biphotons, generating the four polarization Bell states with fidelities reaching 93 percent, comparable to the highest-quality entangled photon sources in atomic systems. Measurements of the Clauser-Horne-Shimony-Holt parameter yielded a value verifying the survival of nonlocal correlations, a key indicator of quantum entanglement.
The team achieved this high fidelity by carefully controlling the atomic configuration and utilizing etalons to filter and isolate the desired spatial modes. This work establishes a practical interface for integrating atomic OAM resources with polarization-based networks, paving the way for versatile entanglement-transfer capabilities in hybrid quantum networking architectures. The narrowband characteristics of the atomic biphotons, combined with this new interface, offer significant advantages for long-distance quantum communication and complex quantum information processing.
Cold Atoms Generate High-Fidelity Polarization Entanglement Scientists have demonstrated the generation of polarization-entangled photons from a cold-atom system, overcoming intrinsic constraints that typically favor orbital angular momentum (OAM)–based entanglement. This was achieved by coherently transferring a selected component of the photons’ OAM into the polarization degree of freedom, thereby enabling access to polarization entanglement that is otherwise unavailable in such systems. Quantum state tomography confirms that biphoton coherence is preserved throughout the mapping process. The resulting photon pairs show high entanglement quality, with fidelities ranging from 92% to 94% across the four Bell states and a Clauser–Horne–Shimony–Holt (CHSH) parameter of 2.44, verifying the presence of strong nonlocal correlations. The study further indicates that any observed decoherence arises from technical factors—such as mode projection inefficiencies and phase instability—rather than from fundamental limitations of the atomic system itself. This work establishes a practical interface between atomic platforms that exploit orbital angular momentum and existing polarization-based quantum communication networks. While the data do not fully disentangle technical noise from potential intrinsic decoherence mechanisms, the results are consistent with technical imperfections being the dominant source. Future research may extend this approach to higher-dimensional photonic encodings and combine mode-selective mapping with temporal gating, opening pathways toward high-dimensional time-bin entanglement. Overall, this achievement marks an important advance toward hybrid quantum networks that integrate atomic resources with polarization-compatible quantum communication technologies. 👉 More information 🗞 Polarization Entanglement in Atomic Biphotons via OAM-to-Spin Mapping 🧠 ArXiv: https://arxiv.org/abs/2512.11625 Tags: