Lasing in circuit quantum electrodynamics with strong noise

We study a model which can describe a superconducting single electron transistor (SSET) or a double quantum dot coupled to transmission-line oscillator. In both cases the degree of freedom is given by a charged particle, which couples strongly to the electromagnetic environment or phonons. We consider the case where a lasing condition is established and study the dependence of the average photon number in the resonator on the spectral function of the electromagnetic environment. We focus on three important cases: a strongly coupled environment with a small cut-off frequency, a structured environment peaked at a specific frequency and 1/f-noise. We find that the electromagnetic environment can have a substantial impact on the photon creation. Resonance peaks are in general broadened and additional resonances can appear

Photon-Number Squeezing in Circuit Quantum Electrodynamics

A superconducting single-electron transistor (SSET) coupled to an anharmonic oscillator, e.g., a Josephson junction-L-C circuit, can drive the latter to a nonequilibrium photon number state. By biasing the SSET in a regime where the current is carried by a combination of inelastic quasiparticle tunneling and coherent Cooper-pair tunneling (Josephson quasiparticle cycle), cooling of the oscillator as well as a laser like enhancement of the photon number can be achieved. Here we show, that the cut-off in the quasiparticle tunneling rate due to the superconducting gap, in combination with the anharmonicity of the oscillator, may create strongly squeezed photon number distributions. For low dissipation in the oscillator nearly pure Fock states can be produced.Comment: 5 pages, 5 figure

Irreversibility on the Level of Single-Electron Tunneling

We present a low-temperature experimental test of the fluctuation theorem for electron transport through a double quantum dot. The rare entropy-consuming system trajectories are detected in the form of single charges flowing against the source-drain bias by using time-resolved charge detection with a quantum point contact. We find that these trajectories appear with a frequency that agrees with the theoretical predictions even under strong nonequilibrium conditions, when the finite bandwidth of the charge detection is taken into account