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 90 people, including over 20 PhDs, has over 20 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: We are seeking a Senior Quantum RF Engineer to lead the design, integration, and validation of RF and microwave systems for quantum-computing hardware. You will develop low-noise, high-fidelity signal chains supporting quantum-device control and readout, from room-temperature electronics through cryogenic interconnects and device packaging.   Key responsibilities: You will design RF and microwave architectures for quantum control, readout, amplification, and signal routing. You will develop components and subsystems including filters, amplifiers, mixers, couplers, resonators, attenuators, bias networks, and impedance-matching structures. You will design and validate room-temperature and cryogenic RF signal chains. You will perform electromagnetic simulation, link-budget analysis, noise analysis, and signal-integrity optimization. You will characterize components and systems using vector network analyzers, spectrum analyzers, signal generators, oscilloscopes, and noise-measurement equipment. You will optimize phase noise, noise figure, gain, linearity, isolation, bandwidth, cross-talk, and thermal loading. You will develop calibration, de-embedding, and automated test procedures. You will support the integration of RF electronics with quantum processors, cryostats, interposers, PCBs, cables, connectors, and advanced packaging. You will diagnose performance limitations involving reflections, interference, grounding, shielding, drift, and thermal effects. You will define requirements, interfaces, test plans, and acceptance criteria for RF subsystems. You will lead technical reviews and collaborate with quantum scientists, electronics engineers, packaging teams, firmware developers, and external suppliers. You will mentor junior engineers and contribute to RF design standards, technology roadmaps, and laboratory best practices. ABOUT YOU: * Master’s degree or PhD in electrical engineering, applied physics, quantum engineering, or a related field. * You have substantial experience designing and testing RF or microwave systems. * You have strong knowledge of S-parameters, impedance matching, transmission lines, resonators, noise, nonlinearities, and signal integrity. * You have experience with electromagnetic and circuit-simulation tools such as Ansys HFSS, CST Studio Suite, Keysight ADS, or equivalent. * You have hands-on experience with RF laboratory instrumentation and measurement techniques. * You have experience designing RF PCBs, microwave assemblies, or integrated interconnects. * You have proficiency with Python, MATLAB, or similar tools for automation and data analysis. * You have demonstrated ability to lead complex technical projects and resolve multidisciplinary engineering problems.   Really nice to have:  * Experience with superconducting, semiconductor-spin, trapped-ion, neutral-atom, or other quantum-computing platforms. * Knowledge of qubit control and dispersive readout techniques. * Experience developing systems operating at cryogenic temperatures. * Familiarity with cryogenic amplifiers, circulators, isolators, parametric amplifiers, and superconducting microwave devices. * Experience with IQ modulation, direct digital synthesis, FPGA-based control, multiplexed readout, or real-time feedback. * Understanding of electromagnetic compatibility, packaging effects, thermalization, and magnetic shielding. * Experience transitioning RF systems from laboratory prototypes to reliable, scalable products. * Record of technical leadership, patents, publications, or contributions to complex research programs. WHAT WE OFFER: What we offer:  66,000 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 want to have a key role in a growing startup with challenges at the frontier of the 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 60-people team 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!