Towards a scalable superconducting qubit architecture

Pierre-Marie Billangeon, Yasunobu Nakamura

Simon Lang, Christoph Kutter, I. Eisele +1 more

Ferdinand Helmer, M. Mariantoni, Austin G. Fowler +3 more

We propose an architecture for quantum computing based on superconducting circuits, where on-chip planar microwave resonators are arranged in a two-dimensional grid with a qubit at each intersection. This allows any two qubits on the grid to be coupled at a swapping overhead independent of their distance. We demonstrate that this approach encompasses the fundamental elements of a scalable fault-tolerant quantum-computing architecture.

Runqi Kang, Q. P. Hu, Xiao Cai +4 more

The dark photon is a well-motivated dark matter candidate that appears in many extensions of the standard model. A fundamental mass-range-sensitivity dilemma is always haunting the dark photon search experiments: resonant haloscopes have excellent sensitivity but are narrowband, while nonresonant haloscopes are broadband but not as sensitive as the resonant ones. A scalable architecture integrating numerous resonant haloscopes would be a desirable solution to this dilemma. However, even the concept of a scalable search remains rarely explored due to the size limitation of conventional haloscopes imposed by the dark photon wavelength. Here, we propose and demonstrate a novel architecture using superconducting qubits as subwavelength haloscope units. By virtue of the scalability of superconducting qubits, it is possible to integrate multiple qubits with different frequencies on a chip-scale device. Furthermore, the frequencies of the qubits can be tuned to extend the search mass range. Thus, our scalable architectures allow for sweepable high-sensitivity dark photon searches at multiple frequencies simultaneously. As a proof-of-principle experiment, we designed and fabricated a three-qubit chip and successfully demonstrated a scalable dark-photon search. Our Letter established constraints on dark photons in the mass range of 15.632-15.638, 15.838-15.845, and 16.463-16.468 μeV, simultaneously, and the constraints are much more stringent than the cosmology constraints. In the future, our Letter can be scaled up to boost the scrutiny of new physics.

Ze Zhan, Zishuo Li, Fei Wang +24 more

Superconducting quantum processors have largely converged on transmon-based architectures, while alternative qubit modalities with intrinsic error protection have lacked a demonstrated path to scalable system integration. In particular, although tunable-coupler-mediated interactions have been validated for small fluxonium systems, it remains unclear whether such designs can be scaled to a multi-qubit lattice. Here, we establish a scalable fluxonium processor architecture based on a modular qubit-coupler unit cell engineered to suppress residual interactions and spectator errors in a many-qubit lattice. The system enables parallel single-qubit gate fidelities approaching 99.99% and two-qubit CZ gate fidelities around 99%. With an optimized gate duration of 32 ns, the best CZ gate fidelity reaches 99.9%. We further validate this architecture in a 22-qubit processor based on the same configuration, where parallel operations enable the deterministic generation of Greenberger-Horne-Zeilinger states involving up to 10 qubits. Together, these results demonstrate that the fluxonium-tunable-coupler unit cell composes without emergent interaction pathologies and establish fluxonium as a scalable superconducting qubit platform.

Joseph Suttle, Neereja Sundaresan, Srikanth J. Srinivasan +10 more