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

光子学和量子电子学目前是物理学中发展最快的领域之一，因为它们与未来的信息处理、通信和传感具有至关重要的相关性。这些场处理自然界中的两个基本量子，即光子和电荷载流子，根据量子电动力学理论绑定在一起。然而，探索量子导体的量子光学的发展直到最近才作为一个交叉学科领域出现，在通过量子电子学创造和控制量子微波辐射方面具有新的前景。特别强大的是基于超导量子电路关键部件的器件，即直流偏压约瑟夫森结(JJ)和微波谐振器。它们允许达到强电荷-光相互作用的领域，结合基本完美地将电能转化为光子能量。在第一个资助期(2017-2021年)，并与我们在CEA Saclay的法国合作伙伴密切合作，我们大力推动了约瑟夫森光子学这一新领域的发展。描述和发展了用于单光子和纠缠微波光子的多用途明亮源，并探索了超出量子电阻的高阻抗区域的基本性质。然而，可能的技术应用仍然受制于一个关键的缺点，即低电压波动引起的相扩散。这一延续计划的目标是解决这一问题，特别是在强电荷-光耦合(有效精细结构常数约为1)的情况下，初步实验数据显示存在多达9个光子的多光子共振。这不仅为量子微波工程提供了令人着迷的新工具，也为研究新的物理，即量子区域的相位稳定(量子锁定)铺平了道路，在这种区域可能会发生量子相位滑移，有望通过实验进行监测。作为推广，我们将考虑基本约瑟夫森光子元件的网络，以揭示同步的量子特性，并展望在太赫兹区域发展相位同步高强度源的前景。这项工作计划的一个重要部分将是继续与我们在CEA/Saclay的实验合作伙伴进行卓有成效和成功的合作。

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.