Superconducting micromasers

by Prof. Valentina Brosco (Sapienza - Università di Roma)

Thursday 9 Apr 2009, 15:00 → 17:00 Europe/Rome

Aula Conversi (Dip. di Fisica - Ed. Marconi)

In a number of recent experiments superconducting nanocircuits coupled on chip to electrical resonators displayed quantum electrodynamic effects opening the field of "circuit QED". By creating a population inversion between two charge states in a biased superconducting single-electron transistor coupled to a microstripline resonator, O. Astafiev et al. [Nature 449, 588 (2007)] realized experimentally for the first time a superconducting micromasers. This device is essentially different from conventional (many atoms) masers: one single artificial atom is strongly excited and strongly coupled to the resonator. After an introduction to superconducting quantum circuits and their application to circuit QED, we discuss the spectral properties of the resonator field in superconducting micromasers. We explain many of the experimental observations, showing that strong coupling can lead to a double peak structure in the spectrum and that low-frequency noise is responsible for the inhomogeneous broadening of the maser line. Furthermore we discuss phase locking induced by an additional coherent driving of the resonator.