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arXiv:2605.12018 · PRX Quantum

Enabling Deterministic Passive Quantum State Transfer with Giant Atoms

Oliver Diekmann, Enrico Di Benedetto, Nicolas Jungwirth, Daniele De Bernardis, Zeyu Kuang, Francesco Ciccarello, Stefan Rotter, Peter Rabl, Alejandro Gonzalez-Tudela, Carlos Gonzalez-Ballestero

quant-phSubmitted May 12, 2026• Announced May 13, 2026• 0 citations• Revised May 28, 2026 (v2)

v1 · May 12, 2026 v2 · May 28, 2026 v3 · Sep 15, 2026

Abstract

Achieving quantum state transfer in passive ways can become a powerful asset for scalable quantum networks. Here, we demonstrate how giant atoms coupled to 1D waveguides provide a platform for such a passive, deterministic transfer. Engineering the position and strength of coupling points, we show that the nonlocal interaction can be utilized for the emission of time-reversal-symmetric single-photon wavepackets by spontaneous decay. We first derive general analytical conditions under which arbitrary qubit decays can be mapped to wavevector-dependent couplings that guarantee perfect state transfer in the continuum limit of infinitely many coupling points. Then, for experimentally relevant configurations with a finite number of coupling points, we demonstrate that high transfer fidelities can still be achieved by optimization, reaching 87% with only two coupling points and exceeding 99% with ten or more. We further analyze the robustness of the protocol against disorder in leg positioning and extend the formalism to environments with nonlinear dispersion, showing that dispersion-induced distortions can be fully compensated by judiciously chosen setups. Our results establish giant atoms as a powerful platform for realizing high-fidelity quantum state transfer in a setting without time-dependent control, opening new avenues for scalable quantum networks and engineered light-matter interfaces.

Journal reference: PRX Quantum 7, 043013 (2026)
DOI: 10.1103/6wcb-nj42
Comments: 14 pages, 6 figures

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Three-qubit gates are highly beneficial operations in quantum computing, enabling compact implementations of quantum algorithms and efficient generation of multipartite entangled states. However, realizing such gates with high fidelity remains challenging due to crosstalk, complex control requirements, and the overhead of parametric or tunable couplers. In this work, we propose and analyze the implementation of fast, high-fidelity three-qubit gates using giant atoms -- artificial atoms coupled to a waveguide at multiple spatially separated points. By leveraging interference effects intrinsic to the giant-atom architecture, we demonstrate that native three-qubit gates, such as the controlled-CZ-SWAP (CCZS) and the dual-iSWAP (DIV), can be realized through simple frequency tuning, without the need for complex pulse shaping or additional hardware. We evaluate gate performance under realistic decoherence and show that fidelities exceeding 99.5% are achievable with current experimental parameters in superconducting circuits. As an application, we present a scalable protocol for preparing three- and five-qubit GHZ states using minimal gate depth, achieving high state fidelity within sub-300ns timescales. Our results position giant-atom systems as a promising platform for entangled-state preparation and low-depth quantum circuit design in near-term quantum computers and quantum simulators.

In this paper, we propose a high-fidelity scheme for generating entangled states in a system of two and three giant atoms coupled to the coupled resonator waveguide. Our approach leverages the bound state in the continuum, which is robust against waveguide disorder. Specifically, we achieve a fidelity exceeding

98\%

for Bell state generation, overcoming the limitations of conventional decoherence-free interaction mechanisms. This scheme can be readily extended to a three-giant-atom system for generating W states. In both the two- and three-atom setups, the maximally entangled states are generated in a short time and remain stable even as time approaches infinity. Our proposal is feasible for implementation on state-of-the-art solid-state quantum platforms and significantly broadens the applications of giant atoms and waveguide QED system in quantum information processing.

Parametric amplification offers a powerful means to enhance quantum interactions through field squeezing, yet it typically introduces additional noise which accelerates quantum decoherence, a major obstacle for scalable quantum information processing. The squeezing field is implemented in cavities rather than continuous waveguides, thereby limiting its scalability for applications in quantum simulation. Giant atoms, which couple to waveguides at multiple points, provide a promising route to mitigate dissipation via engineered interference, enabling decoherence-free interactions. We extend the squeezing-amplified interaction to a novel quantum platform combining giant atoms with traveling-wave parametric waveguides based on

χ^{(2)}

nonlinearity. By exploiting destructive interference between different coupling points, the interaction between giant atoms is not only significantly enhanced but also becomes immune to squeezed noise. Unlike conventional waveguide quantum electrodynamics without a squeezing pump, the giant emitters exhibit both exchange and pairing interactions, making this platform particularly suitable for simulating many-body quantum physics. More intriguingly, the strengths of these interactions can be smoothly tuned by adjusting the squeezing and coupling parameters. Our architecture thus provides a versatile and scalable platform for quantum simulation of strongly correlated physics and paves the way toward robust quantum control in many-body regimes.

In this paper, we propose a high-fidelity scheme for generating entangled states in a system of two and three giant atoms coupled to the coupled resonator waveguide. Our approach leverages the bound state in the continuum, which is robust against waveguide disorder. Specifically, we achieve a fidelity exceeding

98%

for Bell state generation, overcoming the limitations of conventional decoherence-free interaction mechanisms. This scheme can be readily extended to a three-giant-atom system for generating

W

states. In both the two- and three-atom setups, the maximally entangled states are generated in a short time and remain stable even as time approaches infinity. Our proposal is feasible for implementation on state-of-the-art solid-state quantum platforms and significantly broadens the applications of giant atoms and waveguide QED systems in quantum information processing.