This episode is a first for the show - a repeat of a previously posted interview on The New Quantum Era podcast! I think you'll agree the reason for the repeat is a great one - this episode, recorded at the APS Global Summit in March, features a conversation John Martinis, co-founder and CTO of QoLab and newly minted Nobel Laureate! Last week the Royal Swedish Academy of Sciences made an announcement that John would share the 2025 Nobel Prize for Physics with John Clarke and Michel Devoret “for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.” It should come as no surprise that John and I talked about macroscopic quantum mechanical tunnelling and energy quantization in electrical circuits, since those are precisely the attributes that make a superconducting qubit work for computation.

The work John is doing at Qolab, a superconducting qubit company seeking to build a million qubit device, is really impressive, as befits a Nobel Laureate and a pioneer in the field. In our conversation we explore the strategic shifts, collaborative efforts, and technological innovations that are pushing the boundaries of quantum computing closer to building scalable, million-qubit systems.

Key Highlights

• Emerging from Stealth Mode & Million-Qubit System Paper:
  • Discussion on QoLab’s transition from stealth mode and their comprehensive paper on building scalable million-qubit systems.
  • Focus on a systematic approach covering the entire stack.
• Collaboration with Semiconductor Companies:
  • Unique business model emphasizing collaboration with semiconductor companies to leverage external expertise.
  • Comparison with bigger players like Google, who can fund the entire stack internally.
• Innovative Technological Approaches:
  • Integration of wafer-scale technology and advanced semiconductor manufacturing processes.
  • Emphasis on adjustable qubits and adjustable couplers for optimizing control and scalability.
• Scaling Challenges and Solutions:
  • Strategies for achieving scale, including using large dilution refrigerators and exploring optical communication for modular design.
  • Plans to address error correction and wiring challenges using brute force scaling and advanced materials.
• Future Vision and Speeding Up Development:
  • QoLab’s goal to significantly accelerate the timeline toward achieving a million-qubit system.
  • Insight into collaborations with HP Enterprises, NVIDIA, Quantum Machines, and others to combine expertise in hardware and software.
• Research Papers Mentioned in this Episode:
  • Position paper on building scalable million-qubit systems

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
• The dynamic evolution of error correction and industry competition

Listeners interested in cutting-edge hardware, quantum startup journeys, or the science behind scalable qubit platforms will find this episode essential. Pierre provides unique clarity on why C12’s approach offers both conceptual and practical advantages for the future of quantum computing,