Letter abstract
Nature Physics 4, 612 - 616 (2008)
Published online: 6 July 2008 | doi:10.1038/nphys1019
Subject Categories: Quantum physics | Techniques and instrumentation | Condensed-matter physics
Sisyphus cooling and amplification by a superconducting qubit
M. Grajcar1,2, S. H. W. van der Ploeg1, A. Izmalkov1, E. Il'ichev1, H.-G. Meyer1, A. Fedorov3, A. Shnirman4 & Gerd Schön5
Laser cooling of atoms paved the way for remarkable achievements in quantum optics, including Bose–Einstein condensation and trapping in optical lattices. Recently, superconducting qubits—micrometre-size superconducting circuits—were shown to act as artificial atoms, exhibiting quantum effects such as Rabi oscillations and Ramsey fringes1, 2, 3. Coupling superconducting circuits to resonators brought them into the realm of quantum electrodynamics4, 5, 6, 7 and opened up perspectives for using them as micro-coolers or to create a population inversion inducing lasing behaviour8, 9, 10, 11, 12. Here, we demonstrate so-called Sisyphus cooling13 and amplification of an LC resonator, which consists of an inductor L and a capacitor C, by a superconducting qubit, furthering the analogies between optical and circuit quantum electrodynamics. In quantum optics, the motion of the atom is cooled or amplified by a laser driving its electronic degrees of freedom. In our system, the roles of the two degrees of freedom are played by the levels of the resonator and the qubit. Red-detuned high-frequency driving of the qubit produces cooling, because the low-frequency LC circuit carries out work in the forward and backward oscillation cycle, always increasing the energy of the qubit. For blue-detuning, the same mechanism leads to Sisyphus amplification and a precursor of lasing. Parallel to the experimental demonstration, we analyse these processes theoretically, quantitatively confirming our interpretation.
- Institute of Photonic Technology, PO Box 100239, D-07702 Jena, Germany
- Department of Experimental Physics, Comenius University, SK-84248 Bratislava, Slovakia
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
- Institut für Theoretische Physik, Universität Innsbruck, A-6020 Innsbruck, Austria
- Institut für Theoretische Festkörperphysik and DFG-Center for Functional Nanostructures (CFN), Universität Karlsruhe, D-76128 Karlsruhe, Germany
Correspondence to: M. Grajcar1,2 e-mail: grajcar@fmph.uniba.sk
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