Few-Qubit Lasing in Circuit QED
speaker: Valentina Brosco (Institut für Theoretische Festkörperphysik , Universität Karlsruhe)abstract: Motivated by recent experiments 1, which demonstrated lasing and cooling of the electromagnetic modes in a resonator coupled to a superconducting qubit, we describe the specific mechanisms creating the population inversion, and we study the spectral properties of these systems in the lasing state 2. Different levels of the theoretical description, i.e., the semi-classical and the semi-quantum approximation, as well as an analysis based on the full Liouville equation are compared. We extend the usual quantum optics description to account for strong qubit-resonator coupling and include the effects of low-frequency noise. We focus in particular on the phase coherence and diffusion of the electromagnetic field in the lasing state proving that in the strong coupling regime the phase diffusion rate depends non-monotonically on the qubit-resonator detuning. Due to this non-monotonic behaviour, in single-qubit lasers, the optimal lasing conditions are generally realized out of resonance, an effect which may lead to a double peak structure in the maser spectrum. Finally, in order to clarify the peculiar properties of single qubit lasers, we discuss the modifications occurring in the lasing state when many qubits are coupled to the resonator and the scaling of the diffusion rate with the number of qubits. 1 O. Astafiev et al., Nature 449, 588 (2007); M. Grajcar et al., Nature Physics 4, 612 (2008). 2 S. Andr\’e, V. Brosco, A. Shnirman, and G. Sch\”on Phys. Rev. A 79 053848 (2009); S. Andr\’e, V. Brosco, M. Marthaler, A. Shnirman, and G. Sch\”on, arxiv:0908.4227 (2009).
timetable:
Sat 7 Nov, 15:30 - 16:00, Aula Bianchi Scienze
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