- Dr. Gianluca Aiello - former UniTN MSc student, now PhD graduand at Laboratoire de Physique des Solides, CNRS, Université Paris Saclay, Orsay, France
In this talk I will discuss the properties and the dynamics of a high impedance microwave cavity galvanically coupled to a DC biased Josephson junction. The cavity is realized in granular Aluminum, a disordered superconductor with high kinetic inductance, which allowed us to obtain modes with a high quality factor (up to 20000) and a characteristic impedance of approximately 5 kΩ. The occupation and the properties of the cavity modes are strongly affected by the charge tunneling processes occurring in the junction connected to the cavity. Because the characteristic impedance of the modes is non negligible, compared to the quantum of resistance RK ≈ 25.8 kΩ, high order non linear processes are observed.
At low voltages compared to the superconducting gap of the junction, the dominant process is the inelastic tunneling of Cooper pairs, which populates the different cavity modes. We directly measure the photon emission in one mode at 6 GHz and observe more than 70 emission peaks as a function of bias voltage, a clear signature of the high non-linearity. At larger voltages close to the gap, quasiparticle tunneling dominates. This dissipative process modifies both the resonance frequency and the linewidth of the modes. A quantum treatment of this process in terms of Lamb shift and quantum jumps is required to quantitatively explain our measurements. These results show the potential of granular Aluminum to realize microwave quantum optics experiments in a regime where charge transport and microwave photons are strongly coupled. Q@TN Lab
Dr. Iacopo Carusotto