Podcast Episode Details

Carbon nanotube qubits with Pierre Desjardins

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Episode 66

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Pierre Desjardins is the cofounder of C12, a Paris-based quantum computing hardware startup that specializes in carbon nanotube-based spin qubits. Notably, Pierre founded the company alongside his twin brother, Mathieu, making them the only twin-led deep-tech startups that we know of! Pierre’s journey is unconventional—he is a rare founder in quantum hardware without a PhD, drawing instead on engineering and entrepreneurial experience. The episode dives into what drew him to quantum computing and the pivotal role COVID-19 played in catalyzing his career shift from consulting to quantum technology.

C12’s Technology and Unique Angle

C12 focuses on developing high-performance qubits using single-wall carbon nanotubes. Unlike companies centered on silicon or germanium spin qubits, C12 fabricates carbon nanotubes, tests them for impurities, and then assembles them on silicon chips as a final step. The team exclusively uses isotopically pure carbon-12 to minimize magnetic and nuclear spin noise, yielding a uniquely clean environment for electron confinement. This yields ultra-low charge noise and enables the company to build highly coherent qubits with remarkable material purity.

Key Technical Innovations

• Spin-Photon Coupling: C12’s system stands out for driving spin qubits using microwave photons, drawing inspiration from superconducting qubit architectures. This enables the implementation of a “quantum bus”—a superconducting interconnect that allows long-range coupling between distant qubits, sidestepping the scaling bottleneck of nearest-neighbor architectures.
• Addressable Qubits: Each carbon nanotube qubit can be tuned on or off the quantum bus by manipulating the double quantum dot confinement, providing flexible connectivity and the ability to maximize coherence in a memory mode.
• Stability and Purity: Pierre emphasizes that C12’s suspended architecture dramatically reduces charge noise and results in exceptional stability, with minimal calibration drift, over years-long measurement campaigns—a stark contrast with many superconducting platforms.

Recent Milestones

C12 celebrated its fifth anniversary and recently demonstrated the first qubit operation on their platform. The company achieved ultra-long coherence times for spin qubits coupled via a quantum bus, publishing these results in *Nature*. The next milestone is demonstrating two-qubit gates mediated by microwave photons—a development that could set a new benchmark for both C12 and the wider quantum computing industry.

Challenges and Outlook

C12’s current focus is scaling up from single-qubit demonstrations to multi-qubit gates with long-range connectivity, a crucial step toward error correction and practical algorithms. Pierre notes the rapid evolution of error-correcting codes, remarking that some codes they are now working on did not exist two years ago. The interview closes with an eye on the race to demonstrate long-distance quantum gates, with Pierre hoping C12 will make industry headlines before larger competitors like IBM.

Notable Quotes

• “The more you dig into this technology, the more you understand why this is just the way to build a quantum computer.”
• “We have the lowest charge noise compared to any kind of spin qubit—this is because of our suspended architecture.”
• “What we introduced is the concept of a quantum bus… really the only way to scale spin qubits.”

Episode Themes

• Entrepreneurship in deep tech without a traditional research background
• Technical deep dive on carbon nanotube spin qubits and quantum bus architecture
• Materials science as the foundation of scalable quantum hardware
• The importance of coherence, noise reduction, and tunable architectures in quantum system design

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  Published on 1 month ago