At C12, we’re building quantum computers by crafting the highest quality qubits using ultra-pure materials and perfected processes to control every individual electron. We believe carbon will be central to the next generation of quantum hardware—and our latest breakthrough, published in Nature Communications, confirms our scientific approach.
Carbon nanotubes offer:
These properties make them ideal candidates for building high-quality spin qubits. Combined with our patented fabrication process, which allows precise integration into quantum chips, we can scale this technology with consistency and control.
Crucially, our system couples quantum circuits to a microwave bus—a coplanar resonator that enables long-range coupling between qubits. It is essential for scalability: it would reduce the complexity of controlling dense spin qubit arrays, simplifies fan-out, and creates the opportunity to interface with nearby classical logic—an important step towards overcoming input/output bottlenecks in large-scale quantum chips.
The microwave bus also supports potentially fast and multiplexed readout, a key requirement for quantum error correction. Enhancing qubit connectivity unlocks the architectural flexibility needed for next-generation, high-performance quantum error correction codes.
Together with our collaborators at École Normale Superieure (ENS), we demonstrated the longest coherence time ever achieved in a carbon-based quantum circuit: 1.3 microseconds. That’s a 100x improvement over prior carbon-based results, and 10x better than silicon qubits in similar conditions.
Notably, this result was achieved at 300 millikelvins, a relatively high operating temperature compared to other leading qubit platforms like superconducting qubits. This thermal robustness is another advantage of carbon-based circuits —this enables denser chip architectures and simplifies cryogenic requirements, both critical factors for scaling.
What makes this result particularly meaningful isn’t just the coherence time—it’s the architecture that made it possible.
Our team engineered a circuit quantum electrodynamics (cQED) device where a suspended carbon nanotube hosts a single electron. This nanotube is connected to the microwave cavity, allowing it to couple with photons—the fundamental particles of light.
This suspended geometry eliminates many common noise sources, such as charge traps at interfaces, and creates a low-noise environment ideal for stable quantum operations. The result is a remarkably clean system that preserves quantum states far beyond what was previously thought possible in semiconducting qubits.
Coherence time is a key performance metric for quantum systems. It determines how long a qubit remains in a usable quantum state before noise corrupts it.
Longer coherence means:
This milestone shows that carbon-based architectures can rival and even outperform today’s dominant platforms under the right conditions.
This achievement isn’t just a scientific result. It’s a proof point that our approach—combining materials science, quantum electronics, and advanced device engineering—can push the limits of what’s possible.
At C12, we’re pioneering a new path to utility-scale quantum computing. A path that begins with clean, controllable qubits and leads to full-stack, fault-tolerant machines. A path that’s unique at scale.
As Matthieu Desjardins, CTO and co-founder at C12, says, "This landmark result strengthens our strategic choice to develop a carbon nanotube-based spin qubit technology. Since the inception of C12, we have focused our effort on an architecture coupling spin qubits to superconducting resonators—an approach that satisfies all essential criteria for scalability, especially long-range coupling. The remarkable coherence achieved with our suspended carbon nanotubes confirms that we have made the right technological choice—one we’re excited to enhance further through our latest advances."
Adding to this perspective, Matthieu Delbecq, Assistant Professor at ENS and C12’s scientific advisor, notes: “This coherence time is a breakthrough for carbon-based qubits—but it's just the beginning. The suspended geometry and microwave bus give us the control and flexibility to scale. We're now engineering even cleaner systems to push coherence even further."
For those willing to dive deep into the science behind, read the full paper named “Microsecond-lived quantum states in a carbon-based circuit driven by cavity photons”, which is now live in Nature Communications.
Also, C12 is currently hiring across engineering and research roles, including quantum measurement and PhD (CIFRE) positions. If you’re curious about building quantum computers from the atom up, visit our Careers page to learn more.
