Alice & Bob

Overview

Alice & Bob is a Paris quantum hardware company with a distinctive idea. Most quantum computers use qubits that suffer from two kinds of errors, bit flips and phase flips, and correcting both requires many extra physical qubits. Alice & Bob's cat qubits are engineered so that bit flips become exponentially rare, leaving only phase flips to correct. That could cut the number of physical qubits needed for a useful machine by a large factor.

The company has more than 200 employees, has raised about 130 million euros in total, and works from sites in Paris and Boston. It sells research access to its processors and is building toward a fault-tolerant computer that it expects to deliver by the end of the decade.

History and background

Alice & Bob was founded in 2020 by Théau Peronnin and Raphaël Lescanne, who built the first cat-qubit experiments while working in the research groups around the École Normale Supérieure in Paris and Lyon, Mines Paris, and Inria. The company's name comes from the characters traditionally used to describe quantum communication. The cat-qubit technique it pioneered was later adopted by Amazon's quantum hardware team.

In December 2024 it published a white paper and a five-milestone roadmap, and in January 2025 it raised a 100 million euro Series B, one of the largest rounds for a European quantum startup at the time. In 2026 the venture arm of Nvidia invested, and in June 2026 the company signed a memorandum of understanding with Bull to deepen collaboration on integrating cat-qubit machines into high-performance computing centers.

How the technology works

A cat qubit is named after Schrödinger's cat. Instead of storing information in a single two-level system, it stores a quantum state in a microwave resonator as a superposition of two classical-like states of light. A carefully designed circuit continually pumps and dissipates photons in pairs so that the resonator is pushed back toward those two states. The result is that the rate of bit-flip errors falls exponentially as the average number of photons in the cat state increases, while phase-flip errors rise only linearly.

This asymmetry lets error correction use a simple repetition code against the remaining phase flips, instead of the more demanding two-dimensional codes needed for ordinary qubits. Alice & Bob's Boson 4 chip reported bit-flip times of up to seven minutes in 2024, a record for superconducting qubits at that time, and the company later reported bit-flip lifetimes of more than an hour on a newer design.

The roadmap names its chip series after elements. Boson, which masters the cat qubit, is described as complete. Helium aims to build a below-threshold logical qubit from 18 cat qubits and is in progress in 2026. Lithium connects logical qubits and demonstrates fault-tolerant gates, Beryllium delivers universal gates using magic-state factories, and Graphene, the 2030 target, would pack 100 logical qubits into about 2,000 cat qubits with a logical error rate of one in a million. These targets are plans, not results.

Products and platforms

Processors in our Hardware Database

• Alice & Bob Boson 4 (cat qubit chip) — 1 qubits, released 2024

Key milestones

Strengths and challenges

Strengths

• A design that removes one error type at the hardware level and could sharply reduce qubit overhead.
• Record-setting bit-flip suppression results.
• Strong backing from French and European investors, plus Nvidia.
• A clear, staged public roadmap with named milestones.

Challenges and open questions

• Phase-flip errors still require correction, and the Helium logical qubit has not yet been shown below threshold.
• Cat-qubit gates are harder to engineer than for conventional transmons, and extending the approach to many qubits is unproven.
• The 2030 Graphene target is ambitious, and the company will need to scale from a handful of qubits to thousands.
• Larger competitors, including Google, IBM, and Amazon, have greater resources.

Why it matters

Alice & Bob represents the idea that smarter qubit design, not only more qubits, could be what makes quantum computers practical. If cat qubits deliver their promised hardware efficiency, a useful machine could need far fewer components than the roadmaps of IBM and Google imply.

For students, it is also a clear example of how quantum error correction works in practice. The company's focus on suppressing one error type physically and correcting the other in software shows how hardware and code design can be co-optimized.

Latest news

• Alice & Bob and Bull sign a memorandum of understanding to deepen cat-qubit collaboration for high-performance computing — June 2026
• Nvidia's venture capital arm invests in Alice & Bob — 2026
• Alice & Bob reports bit-flip lifetimes of more than an hour on a new cat-qubit design — Late 2025
• Alice & Bob announces a 50 million dollar advanced quantum lab in Paris — 2025

Frequently asked questions

This profile is written for educational purposes and summarizes public announcements, company filings, and published research. Last reviewed: September 30, 2026. It is not investment advice. Check the company's official channels for the latest figures and claims.

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