Quantum Electric Transport Meets Quantum Optics: Josephson Photonics with Strong Charge-Light Coupling Specifically for the continuation: Strong Light-Matter Coupling in Josephson Photonics: Multi-photon Resonances, Quantum Locking and Synchronization

• Applicant: Professor Dr. Joachim Ankerhold
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459903924

Photonics and quantum electronics are currently among the fastest developing fields in physics due to their paramount relevance for future information processing, communication, and sensing. These fields deal with two fundamental quanta in nature, namely, photons and charge carriers, bound together according to the theory of quantum electrodynamics. However, a development which explores the quantum optics of quantum conductors has emerged only very recently as an interdisciplinary field with new prospects in creating and controlling quantum microwave radiation via quantum electronics. Particularly powerful are devices based on the key components of superconducting quantum electrical circuits, namely, dc-voltage biased Josephson junctions (JJ) and microwave resonators. They allow reaching the domain of strong charge-light interaction in combination with a basically perfect conversion of electrical into photonic energy. In the first funding period (2017-2021) and in close collaboration with our French partners at the CEA Saclay we substantially pushed forward this new field of Josephson Photonics. Bright versatile sources for single and entangled microwave photons have been described and developed and fundamental properties in the high impedance regime beyond the quantum resistance have been explored. However, possible technological applications still suffer from one crucial drawback, namely, phase diffusion by low voltage fluctuations. The goal of this continuation project is to solve this problem, particularly in the regime of strong charge-light coupling (effective fine structure constant on the order of 1), where preliminary experimental data show the existence of multi-photon resonances of up to nine photons. This not only offers fascinating new tools for quantum microwave engineering but also paves the road to investigate new physics, namely, phase stabilization in the quantum regime (quantum locking), where quantum phase slips may occur which are expected to be monitored experimentally. As a generalization, we will consider networks of basic Josephson Photonic elements to reveal quantum properties of synchronization with the prospect to develop phase-synchronized high intensity sources in the THz regime. An essential part of this work program will be the continuation of the very fruitful and successful collaboration with our experimental partners at the CEA/Saclay.

• DFG Programme: Research Grants
• International Connection: France, United Kingdom
• Co-Investigator: Dr. Ciprian Padurariu
• Cooperation Partners: Professor Dr. Andrew Armour; Dr. Daniel Esteve