Towards coherent manipulation of the ground states of single cesium atom confined in a microscopic far-off-resonance optical dipole trap

摘要

This work deals with the cooling and trapping of single cesium (Cs) atoms in a large-magnetic-gradient magneto-optical trap (MOT) and the confinement of single Cs atoms in a far-off-resonance optical dipole trap (FORT). The experiment setup is based on two large-numerical-aperture lens assemblies which allow us to strongly focus a 1064-nm TEM_(00)-mode Gaussian laser beam to a 1/e~2 radius of ~ 2.3 μm to form a microscopic FORT for isolating single atom with environment and to efficiently collect the laser-induced-fluorescence photons emitted by single atoms for detecting and recognizing single atom's internal state. We have tried both of "bottom-up" and "top-down" loading schemes to confine single atoms in the microscopic FORT. In the "bottom-up" scheme, we have successfully prepared single Cs atoms in the MOT and transferred it into FORT with a probability of almost 100%. In the "top-down" scheme, we have achieved ~ 74% of single atom loading probability in the FORT using light-assisted collisions induced by blue detuning laser and with prepared many Cs atoms in the MOT. The relaxation time in hyperfine level of ground state of trapped single Cs atom is measured to be ~5.4 s. To coherently manipulate atomic quantum bits (qubit) encoded in the clock states (mF = 0 states in F_g = 3 and 4 hyperfine levels) of single Cs atom via the two-photon simulated Raman adiabatic passage (STIRAP), we have prepared two phase-locked laser beams with a frequency difference of ~ 9.192 GHz by optically injecting an 852-nm master laser to lock the +1-order sideband of a 9-GHz current-modulated slave diode laser. The two phase-locked laser beams are used to drive STIRAP process in the Λ-type three-level system consists of Cs |6S_(1/2) F_g = 4, m_F = 0> and |6S_(1/2) F_g = 3, m_F = 0< long-lived clock states and Cs |6S_(1/2) F_e = 4, m_F = +1 > excited state with the single-photon detuning of ~ -20 GHz. Rabi flopping experiments are in progress.