Fault-tolerant quantum computing with a microwave Cat Bus

Abstract

The scalability of fault-tolerant neutral-atom quantum computers is constrained by the latency of shuttling with optical tweezers, imposing a stringent trade-off between qubit overhead and circuit depth in quantum algorithm compilation. Here we propose a hardware-efficient, shuttling-free architecture that achieves all-to-all connectivity. Remote Rydberg atoms are resonantly entangled through a microwave ``Cat Bus''---a cavity mode autonomously stabilized in a bosonic cat state. The Cat Bus natively supports the highly parallelized execution of one-to-many $\mathrm{CZ}^n$ gates with exponentially suppressed crosstalk. We derive the resulting cat--atom error channel from the underlying interactions and physical constraints. For fault-tolerant operation, we develop a hardware-aware scheduling scheme that exploits the native cat--atom $\mathrm{CZ}^{n}$ gate to construct a syndrome-extraction circuit with minimum depth. We benchmark the architecture using hypergraph-product (HGP) codes and estimate a 180-fold reduction in syndrome-extraction cycle time at $N=10^5$ data qubits compared with an atom-rearrangement-based architecture. Under matched two-qubit depolarizing noise, the corresponding error threshold increases from $0.55\%$ to $0.72\%$. Under the hardware-derived error model, we obtain a threshold of $0.80\%$, corresponding to a threshold cooperativity of $C_{\mathrm{th}}=7.8 \times 10^4$, compatible with experimentally accessible parameters for Rydberg-coupled microwave-cavity systems. By avoiding atom transport, the Cat Bus provides a route towards high-speed, fault-tolerant neutral-atom quantum computation.

The paper asks whether cavity-mediated interactions can remove atom-shuttling latency from neutral-atom fault-tolerant computing. It proposes a static atom array coupled to crossed rows and columns of microwave resonators, each stabilized in a bosonic cat manifold. Projecting the resonant atom–cavity interaction into this manifold yields approximately commuting conditional rotations, enabling a native cat–atom $\mathrm{CZ}^n$ gate whose duration is independent of target count at fixed cat amplitude. The analysis derives leading photon-loss and Rydberg-decay channels, with optimized process infidelity $\epsilon_{n,\min}=\pi\sqrt{n/(2C)}$ for cooperativity $C=g^2/(\kappa_1\gamma)$. Assumed parameters give a 142 ns native gate. For hypergraph-product codes, syndrome extraction is compiled through star-based scheduling, with minimum depth within the specified scheduling model determined by a minimum vertex cover. The estimated cycle time scales as $N^{1/2}$ and is 180 times shorter than an atom-rearrangement estimate at $N=10^5$ data qubits. Stabilizer-circuit simulations with BP+OSD decoding give thresholds of approximately $0.72\%$ with cat flags versus $0.55\%$ for rearrangement under matched pairwise depolarizing noise. A hardware-derived stochastic model gives $0.80\%$, mapped to $C_{\mathrm{th}}\approx7.8\times10^4$. These are architectural estimates and quantum-memory simulations, not experimental results. Threshold benchmarks assume ideal single-qubit gates, preparation, measurement and idling, and replace atomic leakage by unheralded depolarizing noise. The channel derivation omits finite-dissipative-gap corrections. Large-code logical failure rates are extrapolated from empirical fits; universal fault-tolerant logical gates remain future work.