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A decoherence resilient quantum memory for topological quantum skyrmions

Hong Gao, Chengyuan Wang, Yongkun Zhou, Shuya Zhang, Yun Chen, Jinwen Wang, Xinji Zeng, Dong Wei, Xin Yang, Pei Zhang, Andrew Forbes, Mingtao Cao, FuLi LI

Published Mar 20, 2026• 0 citations
Publisher

Abstract

Abstract Quantum skyrmions as topologically structured quantum photonic states are promising candidates for enabling robust quantum information processing in real-world environments where entanglement is fragile. The state-of-the-art allows their creation as single photon and entangled states, but their storage in a quantum memory is crucial to realise real applications, e.g., quantum repeaters for quantum networks as well as gates and synchronisation for quantum computers. Here we demonstrate the first entanglement mediated quantum memory of quantum skyrmions in cold atomic ensembles. To achieve this, we produce the first narrow-band quantum skyrmions from spontaneous four‑wave mixing, yielding a sub‑natural linewidth compatible with atomic transitions. We then store the spatially encoded photon (one of the entangled pair) in an electromagnetically induced transparency memory, subjecting it to light‑matter interaction and decoherence while its entangled partner remains free, thus demonstrating the first storage and retrieval of quantum topology. Crucially, we observe that the Skyrme number remains resilient even as entanglement decays under storage noise, demonstrating the inherent topological robustness of the non‑local state. Our work establishes cold atomic ensembles as an integrated platform for quantum topological photonics, combining narrowband entanglement generation, reconfigurable topological engineering, and coherent quantum storage. These results bridge structured light, quantum information, and topological physics, and open pathways toward topologically protected quantum repeaters and noise-resilient quantum networks, where topology itself acts as a resource for preserving quantum information.

DOI
10.21203/rs.3.rs-8838054/v1

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•Dec 5, 2013•2 citations
Abstract Quantum skyrmions as topologically structured quantum photonic states are promising candidates for enabling robust quantum information processing in real-world environments where entanglement is fragile. The state-of-the-art allows their creation as single photon and entangled states, but their storage in a quantum memory is crucial to realise real applications, e.g., quantum repeaters for quantum networks as well as gates and synchronisation for quantum computers. Here we demonstrate the first entanglement mediated quantum memory of quantum skyrmions in cold atomic ensembles. To achieve this, we produce the first narrow-band quantum skyrmions from spontaneous four‑wave mixing, yielding a sub‑natural linewidth compatible with atomic transitions. We then store the spatially encoded photon (one of the entangled pair) in an electromagnetically induced transparency memory, subjecting it to light‑matter interaction and decoherence while its entangled partner remains free, thus demonstrating the first storage and retrieval of quantum topology. Crucially, we observe that the Skyrme number remains resilient even as entanglement decays under storage noise, demonstrating the inherent topological robustness of the non‑local state. Our work establishes cold atomic ensembles as an integrated platform for quantum topological photonics, combining narrowband entanglement generation, reconfigurable topological engineering, and coherent quantum storage. These results bridge structured light, quantum information, and topological physics, and open pathways toward topologically protected quantum repeaters and noise-resilient quantum networks, where topology itself acts as a resource for preserving quantum information.
Optical skyrmions are topological structures of light whose defining property, the skyrmion number, is robust against perturbations. This makes them attractive for applications in quantum information storage, where resilience to decoherence is paramount. However, their preservation during coherent storage remains unexplored. We report the first experimental demonstration of storing and retrieving optical skyrmions in a cold 87^{87}87Rb vapor using a dual-path electromagnetically induced transparency memory. Crucially, we show that the skyrmion number remains invariant for storage times up to several microseconds, even when subjected to imbalanced loss between the two paths and substantial perturbations in control beam power. Our work demonstrates the survival of a non-trivial topological invariant in a quantum memory, marking a significant step towards topologically protected photonic technologies.
An open challenge in the context of quantum information processing and communication is improving the robustness of quantum information to environmental contributions of noise, a severe hindrance in real-world scenarios. Here, we show that quantum skyrmions and their nonlocal topological observables remain resilient to noise even as typical entanglement witnesses and measures of the state decay. This allows us to introduce the notion of digitization of quantum information based on our discrete topological quantum observables, foregoing the need for robustness of entanglement. We compliment our experiments with a full theoretical treatment that unlocks the quantum mechanisms behind the topological behavior, explaining why the topology leads to robustness. Our approach holds exciting promise for intrinsic quantum information resilience through topology, highly applicable to real-world systems such as global quantum networks and noisy quantum computers. Recent work reported a non-local quantum entangled state of photons with skyrmionic topology. Here the authors demonstrate theoretically and experimentally that topological properties of this system are resilient to noise, even as entanglement measures decay, and elucidate the mechanisms behind this robustness.
Topological quasiparticles of light, such as classical and quantum optical skyrmions, have so far relied on fully coherent or pure quantum states whose topology is encoded in the entanglement between polarization and two-dimensional spatial modes. Here we show that skyrmionic topology can emerge directly within the density matrix of a mixed quantum state. We introduce a framework in which a coherence-Stokes vector defines a topological texture over the density matrix, enabling the realization of quantum skyrmions using only a pseudospin and a real or synthetic one-dimensional space of modes. For a single photon, the density matrix is analogous to the coherence matrix of classical light, and can be encoded using partially coherent electromagnetic fields. We further analyze the topological texture encoded in a bipartite entangled photon pair, showing how skyrmions arise not only in the full bi-photon system, but also in its reduced subspaces with any pseudospin-mode combination simultaneously. We then explore the robustness of such skyrmions to environmental noise, and discover their persistence in mixed-quantum states of multiple photons. Finally, we propose a feasible experimental route to generate and measure such skyrmions using integrated photonic networks, and suggest avenues for similar implementations in other quantum systems. Our work paves the way for robustly encoding classical information on partially coherent light or on mixed quantum states and for encoding topological charges on many-body quantum systems.
Skyrmions are a particle-like topology with a quantised skyrmion number, realised across condensed matter and photonic platforms alike. In quantum photonics, they constitute an emerging resource, promising robust quantum information encoding, so far realised as single photon and bi-photon entangled states. Here we report the first visualisation of tripartite entanglement dynamics through topological structure using spin-skyrmion entangled states, where the topology of a single photon is remotely controlled through the spin of its entangled partner. We visualise our tripartite state theoretically by introducing the notion of a topological Bloch sphere that completely captures the entanglement and topolological features of the state. By leveraging this state, we realise the first quantum multiskyrmions, comprising multiple localised skyrmions within a single structure, that emulate signatures of their magnetic counterparts. We verify this experimentally and show that traversing our topological sphere reveals entanglement-driven particle-like motion of the localised topological structures. These dynamics unveil a physical manifestation of tripartite entanglement correlations which we illustrate by example of GHZ-like states, enabling a visualisation of multiple Bell states encoded within our system. Our work opens exciting possibilities for quantum sensing by mapping complex quantum channel features onto topological observables of multipartite states and offers a promising avenue for harnessing quantum topologies for multi-level encoding quantum communication schemes.
A quantum memory is a key component for quantum networks, which will enable the distribution of quantum information. Its successful development requires storage of single-photon light. Encoding photons with spatial shape through higher-dimensional states significantly increases their information-carrying capability and network capacity. However, constructing such quantum memories is challenging. Here we report the first experimental realization of a true single-photon-carrying orbital angular momentum stored via electromagnetically induced transparency in a cold atomic ensemble. Our experiments show that the non-classical pair correlation between trigger photon and retrieved photon is retained, and the spatial structure of input and retrieved photons exhibits strong similarity. More importantly, we demonstrate that single-photon coherence is preserved during storage. The ability to store spatial structure at the single-photon level opens the possibility for high-dimensional quantum memories. Photonic quantum memories are necessary for quantum information networks and can be built using cold atomic gases. In this work, Ding et al. show the first storage and retrieval of single photons carrying orbital angular momentum using electromagnetically induced transparency in a cold rubidium ensemble.
Quantum memories are an essential building block for quantum information science, and in particular for the implementation of quantum communications across long distances. A quantum memory is defined as a system capable of storing and retrieving quantum states on-demand, such as quantum bits (qubits). Atomic ensembles are good candidates for this purpose because they enables strong light-matter coupling in case of a large number of atoms. Moreover, the collective effect, enhanced in the regime of large optical depth, can lead to storage efficiency close to unity. Thus, in this thesis, a large magneto-optical trap for cesium atoms is used as a atomic medium in order to implement a quantum memory protocol based on electromagnetically induced transparency (EIT). First, the EIT phenomenon is studied through a criterion for the discrimination between the EIT and the Autler-Townes splitting models. We then report on the implementation of an EIT-based memory for photonic qubits encoded in orbital angular momentum (OAM) of light. A reversible memory for Laguerre-Gaussian modes is implemented, and we demonstrate that the optical memory preserves the handedness of the helical structure at the single-photon level. Then, a full quantum state tomography of the retrieved OAM encoded qubits is performed, giving fidelities above the classical bound. This showed that our optical memory operates in the quantum regime. Finally, we present the implementation of the so-called DLCZ protocol in our ensemble of cold atoms, enabling the generation of heralded single photons. A homodyne detection setup allows us to realize the quantum tomography of the created photonic state.