Fault-tolerant modular quantum computing with surface codes using single-shot emission-based hardware

TL;DR

This paper proposes a fault-tolerant modular quantum computing architecture using emission-based surface codes that generate entangled states in a single shot, improving success rates and thresholds without extensive memory gates.

Contribution

It introduces a novel emission-based scheme for surface codes that produces GHZ states in a single shot, eliminating the need for slow two-qubit memory gates and enhancing fault-tolerance thresholds.

Findings

Achieves fault-tolerance thresholds of approximately 0.19% with modest hardware.

Demonstrates generation of Bell, W, and GHZ states in a single shot.

Improves success rates for entanglement distribution in quantum networks.

Abstract

Fault-tolerant modular quantum computing requires stabilizer measurements across the modules in a quantum network. For this, entangled states of high quality and rate must be distributed. Currently, two main types of entanglement distribution protocols exist, namely emission-based and scattering-based, each with its own advantages and drawbacks. On the one hand, scattering-based protocols with cavities or waveguides are fast but demand stringent hardware such as high-efficiency integrated circulators or strong waveguide coupling. On the other hand, emission-based platforms are experimentally feasible but so far rely on Bell-pair fusion with extensive use of slow two-qubit memory gates, limiting thresholds to $\approx 0.16\%$. Here, we consider a fully distributed surface code using emission-based entanglement schemes that generate GHZ states in a single shot, i.e., without the need for Bell-pair fusions. We show that our optical setup produces Bell pairs, W states, and GHZ states, enabling both memory-based and optical protocols for distilling high-fidelity GHZ states with significantly improved success rates. Furthermore, we introduce protocols that completely eliminate the need for memory-based two-qubit gates, achieving thresholds of $\approx 0.19\%$ with modest hardware enhancements, increasing to above $\approx 0.24\%$ with photon-number-resolving detectors. These results show the feasibility of emission-based architectures for scalable fault-tolerant operation.