Photon decay in circuit QED as a new resource for quantum impurity simulations

We present a new approach to analog simulations of quantum impurity problems in circuit QED. Our approach relies on the phenomenon of single photon decay, which is the decay of a microwave photon into lower energy photons driven by a local quantum non-linearity (impurity) [1, 2]. Although there is no practical analog for a single photon decay in traditional quantum optics, this phenomenon is ubiquitous in the bosonic description of strongly-correlated 1D systems, which is at the heart of the modern understanding of strongly-correlated phenomena. Therefore, photon lifetime data represents the outcome of a non-trivial quantum simulation. As a specific example, we built a system consisting of a weak Josephson junction galvanically embedded into a long section of a high-impedance transmission line. By measuring the photon decay rates and comparing them to a newly developed theoretical model, we successfully verified the simulation outcome in the parameter regime accessible to analytical calculations. Changing the impurity circuit allows us to simulate such important phenomena as electron tunneling in Luttinger liquids and dissipative phase transitions, as well as Kondo physics in and out of equilibrium.
[1] R. Kuzmin et al., arXiv:2010.02099
[2] A. Burshtein et al., arXiv:2010.02630