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1. Singly-excited resonant open quantum system Tavis-Cummings model with quantum circuit mapping

   https://doi.org/10.1038/s41598-023-46138-4  

   Marinkovic, Marina Krstic; Radulaski, Marina (November 2023, Scientific Reports)

   Abstract Tavis-Cummings (TC) cavity quantum electrodynamical effects, describing the interaction ofNatoms with an optical resonator, are at the core of atomic, optical and solid state physics. The full numerical simulation of TC dynamics scales exponentially with the number of atoms. By restricting the open quantum system to a single excitation, typical of experimental realizations in quantum optics, we analytically solve the TC model with an arbitrary number of atoms with linear complexity. This solution allows us to devise the Quantum Mapping Algorithm of Resonator Interaction withNAtoms (Q-MARINA), an intuitive TC mapping to a quantum circuit with linear space and time scaling, whoseN+1 qubits represent atoms and a lossy cavity, while the dynamics is encoded through 2Nentangling gates. Finally, we benchmark the robustness of the algorithm on a quantum simulator and superconducting quantum processors against the quantum master equation solution on a classical computer. 

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2. Quantum optical memory for entanglement distribution

   https://doi.org/10.1364/OPTICA.493732  

   Lei, Yisheng; Kimiaee_Asadi, Faezeh; Zhong, Tian; Kuzmich, Alex; Simon, Christoph; Hosseini, Mahdi (November 2023, Optica)

   Optical photons are powerful carriers of quantum information, which can be delivered in free space by satellites or in fibers on the ground over long distances. Entanglement of quantum states over long distances can empower quantum computing, quantum communications, and quantum sensing. Quantum optical memories are devices designed to store quantum information in the form of stationary excitations, such as atomic coherence, and are capable of coherently mapping these excitations to flying qubits. Quantum memories can effectively store and manipulate quantum states, making them indispensable elements in future long-distance quantum networks. Over the past two decades, quantum optical memories with high fidelities, high efficiencies, long storage times, and promising multiplexing capabilities have been developed, especially at the single-photon level. In this review, we introduce the working principles of commonly used quantum memory protocols and summarize the recent advances in quantum memory demonstrations. We also offer a vision for future quantum optical memory devices that may enable entanglement distribution over long distances. 

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3. Topological Qubits as Carriers of Quantum Information in Optics

   https://doi.org/10.3390/app9030575  

   Jaeger, Gregg; Simon, David; Sergienko, Alexander (February 2019, Applied Sciences)

   Winding number is a topologically significant quantity that has found valuable applications in various areas of mathematical physics. Here, topological qubits are shown capable of formation from winding number superpositions and so of being used in the communication of quantum information in linear optical systems, the most common realm for quantum communication. In particular, it is shown that winding number qubits appear in several aspects of such systems, including quantum electromagnetic states of spin, momentum, orbital angular momentum, polarization of beams of particles propagating in free-space, optical fiber, beam splitters, and optical multiports. 

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4. Entanglement of nanophotonic quantum memory nodes in a telecom network

   https://doi.org/10.1038/s41586-024-07252-z  

   Knaut, C M; Suleymanzade, A; Wei, Y-C; Assumpcao, D R; Stas, P-J; Huan, Y Q; Machielse, B; Knall, E N; Sutula, M; Baranes, G; et al (May 2024, Nature)

   Abstract A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected by fibre optical infrastructure^1–3. Here we demonstrate a two-node quantum network composed of multi-qubit registers based on silicon-vacancy (SiV) centres in nanophotonic diamond cavities integrated with a telecommunication fibre network. Remote entanglement is generated by the cavity-enhanced interactions between the electron spin qubits of the SiVs and optical photons. Serial, heralded spin-photon entangling gate operations with time-bin qubits are used for robust entanglement of separated nodes. Long-lived nuclear spin qubits are used to provide second-long entanglement storage and integrated error detection. By integrating efficient bidirectional quantum frequency conversion of photonic communication qubits to telecommunication frequencies (1,350 nm), we demonstrate the entanglement of two nuclear spin memories through 40 km spools of low-loss fibre and a 35-km long fibre loop deployed in the Boston area urban environment, representing an enabling step towards practical quantum repeaters and large-scale quantum networks. 

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5. Continuous recoil-driven lasing and cavity frequency pinning with laser-cooled atoms

   https://doi.org/10.1038/s41567-025-02854-4  

   Schäfer, Vera_M; Niu, Zhijing; Cline, Julia_R_K; Young, Dylan_J; Song, Eric_Yilun; Ritsch, Helmut; Thompson, James_K (April 2025, Nature Physics)

   Abstract Laser-cooled gases of atoms interacting with the field of an optical cavity are a versatile tool for quantum sensing and the simulation of quantum systems. These systems can exhibit phenomena such as self-organization phase transitions, lasing mechanisms, squeezed states and protection of quantum coherence. However, investigations of these phenomena typically occur in a discontinuous manner due to the need to reload atomic ensembles. Here we demonstrate hours-long continuous lasing from laser-cooled⁸⁸Sr atoms loaded into a ring cavity. The required inversion to produce lasing arises from inversion in the atomic-momentum degrees of freedom, which is linked to the self-organization phase transitions and collective atomic recoil lasing observed previously only in a cyclic fashion. We find that over a broad parameter range, the sensitivity of the lasing frequency to changes in cavity frequency is significantly reduced due to an atomic loss mechanism, suggesting a potential approach for mitigating low-frequency cavity noise. Our findings open opportunities for continuous cavity quantum electrodynamics experiments and robust and continuous super-radiant lasers. 

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