Superinductor-based Quantum Technologies with Ultrastrong Couplings

Superconducting quantum circuits form one of the most promising solid state platforms for quantum computing. This success builds on the naturally large interaction between light, represented by microwave signals, and matter, embodied by superconducting qubits.

Microwave photons are used at every stage of quantum information protocols: qubit manipulation, qubit readout and qubit-qubit coupling. To describe this rich and ubiquitous light-matter interaction, the community has relied so far on the conceptual tools inherited from quantum optics. However, atoms and photons interact weakly, perfectly justifying the use of the rotating wave approximation (RWA), which states that non-resonant processes can be safely neglected. The situation with superconducting circuits is quite different since qubits can literally be wired to transmission lines carrying microwave photons. And limitations of the RWA have already been pointed out for qubit readout or driven-dissipative protocols.

SiUCs will follow a radically new approach: we will harness the potentiality of very large light-matter coupling -often referred to as ultra-strong coupling- instead of fighting it. In order to address this challenging approach in a controlled way, we will develop an architecture based on superinductors. Resonators and transmission lines built from such components display impedances close to the quantum of resistance (RQ~6.5 kOhms) at gigahertz frequencies, with very low losses, allowing a boost in light-matter interaction. SiUCS will more specifically focus on improving the efficiency of qubit operations involving light-matter interactions. In addition, superinductors will be used to engineer a missing device of the superconducting quantum circuit toolbox: the microwave single photon detector. Finally, unique many-body physics associated to ultrastrong couplings will be investigated thanks to purposely designed quantum simulators.


  • Coordinator: Pol Forn Díaz (Institut de Física DÁltes Energies – IFAE, ES)
  • Ioan Pop (Karlsruhe Institute of Technology, DE)
  • Milena Grifoni (Regensburg University, DE)
  • Miroslav Grajcar (Slovak Academy of Science, SK)
  • Nicolas Roch (CNRS, FR)
  • Elisabetta Paladino (CNR, IT)


MID-TERM REPORTING: Presentation of the mid-term results of the project


Call year

Call 2019

Call topic

Q-computation, Q-information sciences

Area of research

Quantum computation, Quantum information sciences

Start date

April 2020


36 (+14) months

Funding support

€ 1 285 916,91

Project status

In Progress