Berlin 2005 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 24: Symposium Nanomechanics
TT 24.4: Fachvortrag
Dienstag, 8. März 2005, 12:00–12:35, TU H104
Cooling and squeezing nanomechanical resonators with Josephson qubits — •Alexander Shnirman1, Peter Rabl2, Ivar Martin3, Lin Tian1,2, and Peter Zoller2 — 1Institut für Theoretische Festkörperphysik, Universität Karlsruhe, D-76128 Karlsruhe — 2Institute for Theoretical Physics, University of Innsbruck, A-6020 Austria — 3Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
We propose an application of a single Cooper pair box (Josephson qubit) for active cooling of nanomechanical resonators. Latest experiments with Josephson qubits demonstrated that long coherence time of the order of microsecond can be achieved in special symmetry points. Here we show that this level of coherence is sufficient to perform an analog of the well known in quantum optics “laser” cooling of a nanomechanical resonator capacitively coupled to the qubit. By applying an AC driving to the qubit or the resonator, resonators with frequency of order 100 MHz and quality factors higher than 103 can be efficiently cooled down to their ground state, while lower frequency resonators can be cooled down to micro-Kelvin temperatures.
In addition we show how the resonator can be driven into a squeezed state by choosing the appropriate coupling to a Josephson charge qubit. The stationary squeezed state of the resonator exhibits a reduced noise in one of the quatrature components by a factor of 0.5 - 0.2. These values are obtained for a 100 MHz resonator with a Q-value of 104 to 105 and for T≈25 mK. We show that the coupling to the charge qubit can be used to detect the squeezed state via measurements of the excited state population. Furthermore, by extending this measurment procedure a complete quantum state tomography of the resonator state can be performed. This provides a universal tool to detect a large variety of different states and to proove the quantum nature of a nanomechanical oscillator.