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Gerd Schön, S. Andre, V. Brosco, J. Hauss, M. Marthaler (University of Karlsruhe, Germany) A. Shnirman (University of Innsbruck, Austria) A. Fedorov (Delft University of Technology, The Netherlands) Several recent experiments on quantum state engineering with superconducting circuits realized concepts originally introduced in the field of quantum optics. Motivated by one such experiment [1] we investigate a Josephson qubit coupled to a slow LC oscillator with frequency (~MHz) much lower than the qubit's energy splitting (~GHz). The qubit is ac-driven to perform Rabi oscillations, and the Rabi frequency is tuned to resonance with the oscillator. The properties of this/ driven circuit QED system/ depend strongly on relaxation and decoherence effects in the qubit [2]. We investigate both one-photon and two-photon qubit-oscillator coupling, the latter being dominant at the symmetry point of the qubit. When the qubit driving frequency is blue detuned, we find that the system exhibits lasing behavior (single-atom laser); for red detuning the qubit cools the oscillator. Similar behavior is expected in an accessible range of parameters for a Josephson qubit coupled to a nano-mechanical oscillator. In a different parameter regime, furthering the analogies between superconducting and quantum optical systems we investigate Sisyphus damping, which is the key element of the Sisyphus cooling protocol, as well as its exact opposite, Sisyphus amplification [3]. [1] E. Il'ichev /et al./, Phys. Rev. Lett. 91, 097906 (2003) [2] Single-qubit lasing and cooling at the Rabi frequency, J. Hauss et al., cond-mat/0701041, Phys. Rev. Lett. in print. [3] Sisyphus damping and amplification by a superconducting qubit, M. Grajcar et al., arXiv:0708.0665 [cond-mat.supr-con] |
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