For a superconducting qubit driven to perform Rabi oscillations and coupled to a slow electromagnetic or nanomechanical oscillator we describe previously unexplored quantum optics effects. When the Rabi frequency is tuned to resonance with the oscillator, the latter can be driven far from equilibrium. Blue detuned driving leads to a population inversion in the qubit and a bistability with lasing behavior of the oscillator; for red detuning the qubit cools the oscillator. This behavior persists at the symmetry point where the qubit-oscillator coupling is quadratic and decoherence effects are minimized. There the system realizes a "single-atom-two-photon laser."

The nucleosynthesis of heavy proton-rich nuclei in a stellar photon bath at temperatures of the astrophysical γ-process was investigated where the photon bath was simulated by the superposition of bremsstrahlung spectra with different endpoint energies. The method was applied to derive (γ,n) cross sections and reaction rates for several platinum isotopes.PACS numbers: 26.30.+k, 98.80.Ft, 26.45.+h The trans-iron nuclei have been synthesized by neutron capture in the s-and r-processes, except the p-nuclei (p for proton-rich), with relative abundances of the order of 0.01 to 1% [1]. The main production mechanism of the p-nuclei is assumed to be photodisintegration in the γ-process, i.e. by (γ,n), (γ,p), and (γ,α) reactions induced on heavier seed nuclei synthesized in the s-and r-processes. Typical parameters for the γ-process are temperatures of 2 ≤ T 9 ≤ 3 (T 9 is the temperature in units of 10 9 K), densities ρ ≈ 10 6 g/cm 3 , and time scales τ in the order of seconds. Several astrophysical sites for the γ-process have been proposed, whereby the oxygenand neon-rich layers of type II supernovae seem to be good candidates. However, no definite conclusions have been reached yet [1], predominantly due to the lack of experimental data for the cross sections and reaction rates of the γ-induced reactions at astrophysically relevant energies. All reaction rates have been derived theoretically using statistical model calculations [1-6].The energy distribution of a thermal photon bath at a temperature T is given by the Planck distributionwhere n γ (E, T ) is the number of γ-rays at energy E per unit of volume and energy interval. In a photon-induced reaction B(γ,x)A the distribution leads to a temperature dependent decay rate λ(T ) of the initial nucleus Bwith the speed of light c and the cross section of the γ-induced reaction σ (γ,x) (E). Obviously, λ is also the production rate of the residual nucleus A. In the following we will focus on photodisintegration by the (γ,n) reactions. A large number of (γ,n) cross sections has been measured over the years [7,8]. However, most of the data have been obtained around the giant dipole resonance (GDR), i.e. at energies much higher than those in stars, and practically no data exist for the p-nuclei. The integrand in Eq. (2) is given by the product of the γ flux c n γ (E, T ), which decreases steeply with increasing energy E, and the cross section σ (γ,x) (E), which increases with E approaching the GDR region. The product leads then to a window at an effective energy E eff with a width ∆ similar to the Gamow window for charged-particle-induced reactions. If one assumes a typical threshold behavior of the (γ,n) cross section close to the threshold energy E thr , the effective energy is approximately given by E eff = E thr + 1 2 kT , and the typical width ∆ is in the order of 1 MeV (Fig. 1). 191 Pt reaction (E thr = 8676 keV) in a thermal photon bath with temperature T9 = 2.5. The Planck distribution nγ (E, T ) (dotted line) and the (γ,n) cross section σ(E) (dashed line) are giv...

Superconducting qubits coupled to electric or nanomechanical resonators display effects previously studied in quantum electrodynamics (QED) and extensions thereof. Here we study a driven qubit coupled to a low-frequency tank circuit with particular emphasis on the role of dissipation. When the qubit is driven to perform Rabi oscillations, with Rabi frequency in resonance with the oscillator, the latter can be driven far from equilibrium. Blue detuned driving leads to a population inversion in the qubit and lasing behavior of the oscillator ("single-atom laser"). For red detuning the qubit cools the oscillator. This behavior persists at the symmetry point where the qubit-oscillator coupling is quadratic and decoherence effects are minimized. Here the system realizes a "single-atom-twophoton laser". Φ Φ x (t) ac J J J M M C L U