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arXiv:2610.16210

Collective Floquet engineering between two distant superconducting artificial atoms

Y. -H. Huang, Jiale Yuan, Z. Q. Niu, Y. -S. Tsai, K. -C. Yu, P. -H. Hsu, K. -M. Hsieh, Haw-Tyng Huang, J. C. Chen, P. Y. Wen, Y. -H. Lin, Z. -R. Lin, Da-Wei Wang, I. -C. Hoi

quant-phSubmitted Oct 12, 2026• Announced Oct 13, 2026• 0 citations
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Abstract

A one-dimensional waveguide is a crucial medium for transferring propagating quantum information between remote qubits, yet the photon-mediated interaction is typically fixed by the static device geometry, qubit parameters, and their couplings to the transmission line. Such an interaction can be engineered to be coherent or dissipative via virtual- or real-photon exchange, respectively, yet its effective strength remains fixed in either case. Here we demonstrate dynamical control over this interaction by applying Floquet engineering to two superconducting qubits coupled to a waveguide terminated by a capacitive mirror. By positioning one qubit at an antinode and the other qubit at a node or an antinode of the resonant standing wave, we realize a Hermitian or non-Hermitian coupling between the two qubits. A periodic flux drive of the qubit frequencies then enables on-demand control of the coherent energy splitting and the collective decay. Our results establish Floquet engineering as a route to dynamically reshape both coherent and dissipative photon-mediated interactions between remote quantum emitters.

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A one-dimensional waveguide is a crucial medium for transferring propagating quantum information between remote qubits, yet the photon-mediated interaction is typically fixed by the static device geometry, qubit parameters, and their couplings to the transmission line. Such an interaction can be engineered to be coherent or dissipative via virtual- or real-photon exchange, respectively, yet its effective strength remains fixed in either case. Here we demonstrate dynamical control over this interaction by applying Floquet engineering to two superconducting qubits coupled to a waveguide terminated by a capacitive mirror. By positioning one qubit at an antinode and the other qubit at a node or an antinode of the resonant standing wave, we realize a Hermitian or non-Hermitian coupling between the two qubits. A periodic flux drive of the qubit frequencies then enables on-demand control of the coherent energy splitting and the collective decay. Our results establish Floquet engineering as a route to dynamically reshape both coherent and dissipative photon-mediated interactions between remote quantum emitters.
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We study the coherent control of microwave photons propagating in a superconducting waveguide consisting of coupled transmission line resonators, each of which is connected to a tunable charge qubit. While these coupled line resonators form an artificial photonic crystal with an engineered photonic band structure, the charge qubits collectively behave as spin waves in the low excitation limit, which modify the band-gap structure to slow and stop the microwave propagation. The conceptual exploration here suggests an electromagnetically controlled quantum device based on the on-chip circuit QED for the coherent manipulation of photons, such as the dynamic creation of laserlike output from the waveguide by pumping the artificial atoms for population inversion.
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We propose and analyze a general scheme to engineer programmable and nonreciprocal interactions in an array of atoms coupled to a photonic waveguide. By subjecting each atom to a local harmonic frequency modulation with a defined phase ${\ensuremath{\theta}}_{i}$, we demonstrate the emergence of effective long-range couplings whose parameters are dynamically controllable. For atoms coupled to a conventional waveguide, the modulation dresses the atomic operators, leading to effective interactions governed by the Bessel function J0{\mathcal{J}}_{0}J0​ whose argument depends on the phase differences $\mathrm{\ensuremath{\Delta}}{\ensuremath{\theta}}_{ij}$. For atoms coupled to a photonic crystal waveguide near its band edge, where the density of states is sharply varying, the modulation can be tuned to selectively activate the J12{\mathcal{J}}_{1}^{2}J12​ term, which simultaneously scales both the coherent and dissipative components of the complex coupling strength ${\mathrm{\ensuremath{\Gamma}}}_{ij}$. Crucially, the spatial profile of the local modulation phases imprints a factor $exp(\mathrm{i}\mathrm{\ensuremath{\Delta}}{\ensuremath{\theta}}_{ij})$ onto the waveguide-mediated coupling strength ${\mathrm{\ensuremath{\Gamma}}}_{ij}$, enabling the synthesis of nonreciprocal quantum interactions. Our approach thus provides a flexible toolbox for simulating a wide range of non-Hermitian Hamiltonians on waveguide-QED platforms.
Photon-mediated interactions between atoms are of fundamental importance in quantum optics, quantum simulations, and quantum information processing. The exchange of real and virtual photons between atoms gives rise to nontrivial interactions, the strength of which decreases rapidly with distance in three dimensions. Here, we use two superconducting qubits in an open one-dimensional transmission line to study much stronger photon-mediated interactions. Making use of the possibility to tune these qubits by more than a quarter of their transition frequency, we observe both coherent exchange interactions at an effective separation of 3λ/4 and the creation of super- and subradiant states at a separation of one photon wavelength λ. In this system, collective atom-photon interactions and applications in quantum communication may be explored.
The radiative properties of quantum emitters are profoundly influenced by their electromagnetic environment. When coupled to a waveguide terminated at one end by a mirror, distant emitters interact strongly via virtual photon exchange, leading to collective superradiant and subradiant states with enhanced or suppressed decay rates. We demonstrate that applying optimal frequency shifts to each emitter enables the formation of perfect single-excitation dark states (i.e. states with zero decay rate) and near-perfect multi-excitation dark states in small ensembles. These collective states can be deterministically prepared with high fidelity using classical driving fields or few-photon pulses propagating along the waveguide. These results, readily implementable in superconducting qubit platforms, open new avenues for quantum information storage, networking and control of light.