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# Quantum Impurity Physics with Microwave Photons

### Moshe Goldstein (Yale University)

#### 17.12.2012 at 10:00

We consider the propagation of microwave photons along an array of superconducting grains with a set of weakly-coupled grains at its center. Quantum fluctuations of charge on the weakly-coupled grains make the process of ?photon splitting? effective. In such a process, an incoming photon may be split into a number of photons of lower energy. The minimal number of photons so created depends on the symmetry properties of the corresponding quantum impurity model. As an example, we consider a specific circuit allowing quantum fluctuations between two charge configurations of two weakly-coupled grains, thus mimicking the behavior of an anisotropic Kondo impurity. We relate the total rate of conversion of incoming photons into the lower-energy ones to the linear dynamic spin susceptibility of the Kondo model. The spectral distribution of the outgoing photons yields information about higher-order local correlations in the quantum impurity dynamics.

A 249 - Theresienstr. 37