project title: Cooling of nanomechanical resonators to ground state
project leader: Prof. Alexander Shnirman
access given (in days): 7
access used (in days): 5
local host: Dr. Tero Heikkilä
home institution: Institute for Theoretical Physics, Univ. of Innsbruck
country of institution: Austria
starting date (yyyy-mm-dd): 2008-03-27
Cooling of a mechanical oscillating beam into its quantum-mechanical ground state has become one of the most fascinating goals of low-temperature science. So far, the lowest phonon occupation numbers achieved have still been rather large n ~ 20, mostly due to spurious heating by the detection setup. Here, we theoretically consider prospects of ground-state cooling of a nanomechanical beam when it interacts non-resonantly with a nearby Josephson charge-phase qubit. This setup offers the advantage that detection of the qubit uses existing techniques, introducing only minimal back-action.
Alexander Shnirman visited the ULTI site in connection to the ULTI users meeting He proposed two methods for cooling electrical resonators coupled to driven quantum two-level systems. The first of these is coined "Sisyphus cooling", where the resonator is coupled to the two-level system biased close to a degenerate point and the system is driven with a near-resonant field. Combination of red-detuned driving and spontaneous emission processes leads to a situation where the resonator has to do work on the qubit, resulting into a cooling of the resonator. The second method is based on coupling an anharmonic resonator close to resonance to Rabi oscillations in the qubit. Now depending on which side of the Rabi resonance the resonator energy resides, it can either cool down or heat up. These concepts can be readily implemented also in mechanical resonators, a topic studied intensively experimentally today in the low temperature community.