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arXiv:2603.14854

Cavity-Free Distributed Quantum Computing with Rydberg Ensembles via Collective Enhancement

Muhammad Ali Shahbaz, Aman Ullah

quant-phSubmitted Mar 16, 2026• Announced Mar 17, 2026• 0 citations• Revised Jun 8, 2026 (v2)
v1 · Mar 16, 2026v2 · Jun 8, 2026
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Abstract

We present a complete protocol for cavity-free quantum networking based on collective enhancement in Rydberg atom ensembles. The scheme combines Rydberg blockade, collectively enhanced light--matter coupling, and phase-matched directional emission to remove the need for optical cavities while retaining efficiencies comparable to cavity-assisted interfaces. The protocol proceeds in three steps: (i)~local control--ensemble entanglement generated by Rydberg blockade with gate fidelity $F_{\mathrm{gate}}\approx 99.93\%$; (ii)~atom--photon conversion through Raman emission from an oblate spheroidal ensemble, yielding directional emission efficiency $η_{\mathrm{dir}}\approx 73\%$ and single-node efficiency $η_{\mathrm{node}}\approx 40\%$; and (iii)~remote atom--atom entanglement via Hong--Ou--Mandel interference, producing Bell states with fidelity $F>97.5\%$. Incorporating quantum memories allows up to $M\approx 100$ retry attempts within a coherence time $T_2>100\,μ\mathrm{s}$, enabling entanglement generation rates of approximately $4\,\mathrm{kHz}$ over a 20~km separation. Collectively enhanced Rydberg ensembles thus provide a practical, cavity-free interface for scalable distributed quantum computing and secure quantum communication.

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arXiv:1006.3633•Physical Review A•Nov 29, 2010•85 citations
We present a complete protocol for cavity-free quantum networking based on collective enhancement in Rydberg atom ensembles. The scheme combines Rydberg blockade, collectively enhanced light--matter coupling, and phase-matched directional emission to remove the need for optical cavities while retaining efficiencies comparable to cavity-assisted interfaces. The protocol proceeds in three steps: (i)~local control--ensemble entanglement generated by Rydberg blockade with gate fidelity Fgate≈99.93%F_{\mathrm{gate}}\approx 99.93\%Fgate​≈99.93%; (ii)~atom--photon conversion through Raman emission from an oblate spheroidal ensemble, yielding directional emission efficiency ηdir≈73%η_{\mathrm{dir}}\approx 73\%ηdir​≈73% and single-node efficiency ηnode≈40%η_{\mathrm{node}}\approx 40\%ηnode​≈40%; and (iii)remote atom--atom entanglement via Hong--Ou--Mandel interference, producing Bell states with fidelity F>97.5%F>97.5\%F>97.5%. Incorporating quantum memories allows up to M≈100M\approx 100M≈100 retry attempts within a coherence time T2>100 μsT_2>100\,μ\mathrm{s}T2​>100μs, enabling entanglement generation rates of approximately 4 kHz4\,\mathrm{kHz}4kHz over a 20km separation. Collectively enhanced Rydberg ensembles thus provide a practical, cavity-free interface for scalable distributed quantum computing and secure quantum communication.
Scalable quantum computers and quantum networks require the combination of quantum processing nodes with efficient light-matter interfaces to distribute quantum information in local or long-distance quantum networks. Neutral-atom arrays have both been coupled to Rydberg states to enable high-fidelity quantum gates in universal processing architectures, and to optical cavities to realize interfaces to photons. However, combining these two capabilities and coupling atom arrays to highly excited Rydberg states in the mode of an optical cavity has been an outstanding challenge. Here we present a novel cavity-coupled Rydberg array that achieves this long-standing goal. We prepare, detect, and control individual atoms in a scalable optical tweezer array, couple them strongly to the optical mode of a high-finesse optical cavity and excite them in a controlled way to Rydberg states. We show that high-cooperativity coupling to an optical cavity -- demonstrated via the dispersive shift of the resonance of the cavity in presence of the atoms -- and strong Rydberg interactions -- demonstrated via the collective enhancement of Rydberg coupling in the atomic array -- can be achieved in our setup at the same spatial location. Our presented experimental platform opens the path to several new directions, including the realization of quantum network nodes, quantum simulation of long-range interacting, open quantum systems and photonic-state engineering leveraging high-fidelity Rydberg control.
Realizing large-scale quantum networks requires the generation of high-fidelity quantum entanglement states between remote quantum nodes, a key resource for quantum communication, distributed computation, and sensing applications. However, entanglement distribution between quantum network nodes is hindered by optical transmission loss and local operation errors. Here, we propose a quantum repeater architecture that synergistically integrates Rydberg-atom quantum processors with optical cavities to overcome these challenges. Our scheme leverages cavity-mediated interactions for efficient remote entanglement generation followed by Rydberg-interaction-based entanglement purification and swapping. Numerical simulations, incorporating realistic experimental parameters, demonstrate the generation of Bell states with 99% fidelity at rates of 1.1 kHz between two nodes in a local-area network (distance 0.1km0.1\phantom{\rule{0.2em}{0ex}}\mathrm{km}0.1km), and can be extended to metropolitan-area (25km25\phantom{\rule{0.2em}{0ex}}\mathrm{km}25km) or intercity (250km250\phantom{\rule{0.2em}{0ex}}\mathrm{km}250km, with the assistance of frequency converters) networks with a rate of 0.1 kHz. This scalable approach opens up near-term opportunities for exploring quantum network applications and investigating the advantages of distributed quantum information processing.
A principal goal of distributed quantum processing is the ability to generate, manipulate, and transfer quantum states between distant nodes of a quantum network. These protocols generally require connecting photonic and material carriers of quantum information. Here we present two experimental realizations of light-matter interfaces that allow for engineered atom-photon interactions in free-space settings. First, we utilize reconfigurable arrays of trapped single atoms to study light scattering in low-dimensional systems. We observe noncollinear phase-matching geometries that have suppressed sensitivity to particle localization. We show that the scattered radiation can be controllably enhanced or diminished as a result of Bragg interference. Such scattering can be used for mapping collective states within an array of neutral atoms onto propagating light fields and for establishing quantum links between separated arrays. Second, we create a quasi-two-level system in a regime of Rydberg excitation blockade for a mesoscopic ensemble of several hundred atoms confined in a magic-wavelength optical lattice. We demonstrate coherent driving and Ramsey interference measurements of light shifts, with timescales on the order of ∼ 10 μs. Whereas the coupling producing the Rabi oscillations is enhanced by a factor of √N, there is no corresponding enhancement for the light shifts. These results may prove useful in applying collective qubits with Rydberg interactions to scalable quantum networking architectures.
Integrating Rydberg-state control of atom-atom interactions with cavity control of atom-light interactions enables the combination of local entangling operations with photon-mediated long-range coupling, measurement, and communication. Such integration is challenging because electric fields generated by charges on cavity optics and by cavity-stabilizing actuators may disturb Rydberg-state coherence. Here, we couple a Rydberg tweezer array to a high-cooperativity optical cavity, suppressing the electric fields produced by cavity length actuation so that the residual field variation of about 3 mV/cm3~\mathrm{mV/cm}3 mV/cm rms does not limit Rydberg coherence. We demonstrate two capabilities that neither system provides alone. First, we use Purcell-enhanced fluorescence to read out atoms directly in the ground-Rydberg basis within 7.5 μs7.5~μ\mathrm{s}7.5 μs, well within the Rydberg-state lifetime, with ground- and Rydberg-state detection infidelities of 3%3\%3% and 5%5\%5%, respectively, and with low atom loss. Second, we use Rydberg-Rydberg interactions to control collective light-atom scattering into the cavity mode. Specifically, we drive blockaded Rabi oscillations between a state with two ground-state atoms, which scatter collectively with a superradiant or subradiant rate controlled by the atomic positions, and an entangled state with a single Rydberg excitation, which scatters like a single atom. These capabilities open routes toward networked Rydberg processors, mid-circuit measurements in analog quantum simulators, and many-body quantum optics with entangled emitters coupled collectively to light.
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The realization of a Jaynes-Cummings model in the optical domain is proposed for an atomic ensemble. The scheme exploits the collective coupling of the atoms to a quantized cavity mode and the nonlinearity introduced by coupling to high-lying Rydberg states. A two-photon transition resonantly couples the single-atom ground state $|g\ensuremath{\rangle}$ to a Rydberg state $|e\ensuremath{\rangle}$ via a nonresonant intermediate state $|i\ensuremath{\rangle}$, but due to the interaction between Rydberg atoms only a single atom can be resonantly excited in the ensemble. This restricts the state space of the ensemble to the collective ground state $|G\ensuremath{\rangle}$ and the collectively excited state $|E\ensuremath{\rangle}$ with a single Rydberg excitation distributed evenly on all atoms. The collectively enhanced coupling of all atoms to the cavity field with coherent coupling strengths which are much larger than the decay rates in the system leads to the strong coupling regime of the resulting effective Jaynes-Cummings model. We use numerical simulations to show that the cavity transmission can be used to reveal detailed properties of the Jaynes-Cummings ladder of excited states and that the atomic nonlinearity gives rise to highly nontrivial photon emission from the cavity. Finally, we suggest that the absence of interactions between remote Rydberg atoms may, due to a combinatorial effect, induce a cavity-assisted excitation blockade whose range is larger than the typical Rydberg dipole-dipole interaction length.