Alice & Bob Reports Cat-Qubit Progress in French Quantum Computing Program

Introduction

Alice & Bob, a French fault‑tolerant quantum‑computing firm, has released a progress report on Phase 1 of the French government’s PROQCIMA programme. The effort, coordinated by the French Defense Innovation Agency (AID) and the Direction générale de l’Armement, aims to deliver two universal quantum‑computer prototypes capable of supporting 1,000 logical qubits by 2032. In its first four‑year phase, Alice & Bob was tasked with demonstrating the core operations of its cat‑qubit error‑correction architecture on real hardware.

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Demonstrated hardware capabilities

Alice & Bob built three independent demonstrators – two on 6‑qubit chips and one on a 12‑qubit chip – and reported the following milestones:

• Noise‑biased CNOT gates between cat qubits that preserve intrinsic protection against bit‑flip errors, a prerequisite for the bias‑preserving error‑correction scheme.
• Measure‑and‑reset cycles for auxiliary qubits, enabling rapid syndrome extraction and preparation for subsequent correction rounds. Performance metrics were broadly aligned with PROQCIMA targets.
• Repeated distance‑3 repetition‑code cycles across three data qubits, representing the smallest code capable of correcting a single quantum error.
• Logical error‑rate measurement across the full register. While the rate was quantified, it has not yet dropped below the theoretical error‑correction threshold.
• A non‑Clifford gate on a cat qubit, an essential step toward universal fault‑tolerant computation and the generation of “magic states.”

These results confirm that each building block of Alice & Bob’s cat‑qubit logical qubit can be realized on physical hardware, providing a concrete foundation for further scaling.

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Digital twin and automated monitoring

Alongside the hardware experiments, Alice & Bob developed a digital twin of its processor. By feeding measured performance data into the twin, simulations identified qubit‑coherence consistency as the primary lever for pushing logical error rates below the fault‑tolerance threshold.

The company also deployed its proprietary MnR (monitoring and recalibration) software, which runs continuously when the quantum‑processing unit (QPU) is idle. The system tracks more than 50 performance indicators per qubit, automatically detecting drift and triggering recalibration. This automation reduces downtime—previously a drift‑correction could consume up to a full day—thereby keeping the processor at a stable performance level.

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Outlook within PROQCIMA

PROQCIMA is structured as a ten‑year competition: after the initial four‑year assessment, three candidates will continue, with two ultimately selected for the final eight‑year development phase. Alice & Bob joins four other French firms—Pasqal, Quandela, Quobly, and C12—in the first‑phase cohort.

The Phase 1 report underscores that the cat‑qubit approach is technically viable, yet achieving fault tolerance will require further improvements in qubit coherence and error‑rate reduction. The digital twin and MnR tools provide a roadmap for these enhancements, positioning Alice & Bob to remain competitive as the programme narrows to the final candidates.

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Practical takeaways

• Proof of concept achieved – All core cat‑qubit operations have been demonstrated on real chips.
• Logical error rates still above threshold – Continued work on coherence and error mitigation is essential.
• Automation matters – The MnR system illustrates how software can dramatically improve QPU uptime and consistency.
• Strategic positioning – Successful Phase 1 results keep Alice & Bob in contention for the next PROQCIMA stage, where scaling to 1,000 logical qubits will be the ultimate test.

Alice & Bob’s progress marks a significant step toward fault‑tolerant quantum computing in France, highlighting both the promise of cat‑qubits and the engineering challenges that remain.