Founded in 2020 and based in the heart of Paris, C12’s mission is to be at the center of one of the biggest technological breakthroughs of the century and change the course of history by building a universal quantum computer. At C12, we believe that achieving a true breakthrough in quantum computing requires rethinking the fundamentals. That’s why our founders—deeply rooted in academic and engineering excellence—have chosen carbon nanotubes as the building blocks of our quantum processors. This ultra-pure material dramatically reduces error rates, boosts performance, and minimizes hardware overhead—key ingredients for scalable, fault-tolerant quantum computing. By crafting a unique approach that scales, we aim to revolutionize quantum computing just as silicon transformed classical computing.   Since our founding, we’ve raised over €25 million in funding, published 11 scientific papers, and secured 8 patents. Today, our fast-growing team of 80+, including 25 PhDs, has over 26 nationalities represented. We have our own cutting-edge lab spaces in Paris' historic Panthéon district, where scientists, engineers, and innovators work side-by-side to tackle some of the most exciting technical challenges of our time.   If you're passionate about shaping the future of quantum technology and want to make a real impact, C12 offers a unique environment to grow, learn, and innovate. YOUR ROLE AT C12 QUANTUM ELECTRONICS: As Thermal Modeling & Cryogenic Systems Engineer (Quantum Hardware), you will play a central role in enabling the next generation of our quantum computers. You will own the thermal architecture and thermal models of complex cryogenic quantum systems that combine a growing number of qubits with increasingly sophisticated cryo-electronics. Your work will be critical to ensuring system scalability, thermal stability and quantum performance. You will operate at the intersection of cryogenics, thermal physics, electronics, and quantum hardware whilst working closely with quantum physicists and engineers.    Key responsibilities: Develop and maintain system-level thermal models of quantum hardware systems, including qubits, wiring, passive components, and cryo-electronics across all cryogenic stages Work closely with system engineers and physicists to identify thermal constraints and scaling bottlenecks, evaluate architecture options and guide system design decisions. Own the thermal budget, including trade-off analysis of different technological options (qubit architectures, wiring schemes, cryo-electronics integration levels, materials) Own the thermal performance of cryogenic quantum hardware platforms by defining and executing validation experiments, correlating predictions with measurements, investigating discrepancies and implementing solutions to inform thermal and system architecture decisions Design and evaluate thermalization strategies for signals, wiring, and cryo-electronics, including materials and interfaces, to minimize heat loads while preserving signal integrity. Participate in the integration and operation of cryogenic test platforms, including instrumentation, thermal characterization and investigation of unexpected system behavior Document thermal assumptions models, and design rules to support product development ABOUT YOU: You have a Masters or PhD in Mechanical Engineering, Physics, Cryogenics or a closely related field with at least 3 years of experience in industry You have a strong background in thermal engineering and cryogenics You have proven experience building and maintaining thermal models to guide design decisions You are comfortable working across disciplines with quantum hardware, electronics, and systems teams You are hands-on with dilution refrigerators and multi-stage cryogenic platforms You have demonstrated expertise in thermal modeling and simulation using analytical and numerical methods. You have experience defining and managing thermal budgets in systems with dense wiring and/or cryo-electronics You are familiar with RF and DC wiring, signal thermalization and heat sinking at cryogenic temperatures You have experience validating thermal models through experimental measurements and data analysis You have programming or scripting experience for data analysis and model automation (e.g. Python, Matlab) Prior experience in quantum hardware, superconducting systems, or other ultra-low-temperature technologies is a strong plus WHAT WE OFFER:  * 65,000 euros - 78,000 euros yearly base salary  * Stock options for every employee (BSPCE/ESOP) * Sponsored trip to conferences around the world * A highly dynamic international team * Swile meal vouchers * Mental health support with moka.care * Training budget/ Annual Learning & Development Allowance * Sabbatical leave (after 2 years in the company) * Vibrant office culture (two office spaces in the heart of Paris, team lunches, offsite events, Friday breakfasts..)   YOU SHOULD JOIN US IF... * You like hands-on work and technology * You want to contribute to achieving landmark results in quantum computing, making a difference in the emerging quantum technologies * You want to work within a team of 80+ people with various backgrounds in nanofabrication, quantum electronics, and carbon nanotube science to create a revolutionary quantum computing processor * You want to thrive in an exceptional scientific environment with several industrial and academic partners * You share our values (excellence, scientific integrity, diversity, curiosity, and care) and want to help us define our product-focused culture and ambition to accelerate   We still encourage even if you don’t meet all the requirements. Rest assured, we are committed to finding the right fit for our team and are open to adjusting compensations based on skills and experiences. Applications from women are especially welcomed!