Generation and application of two-photon Raman laser for manipulation of internal state of Cs atom

Abstract

Two-photon Raman process (TPRP) is an important technique in controlling the atomic internal states. It plays an important role in quantum manipulation and quantum information process. A reliable Raman laser for specific atom is the first step to demonstrate TPRP and quantum manipulation of an atom. In this paper, we theoretically analyze the two-photon Raman process regarding to Cesium “clock states” |6S1/2, F=4, mF=0 and |6S1/2, F=3, mF=0, and we obtain the dependences of the corresponding Rabi frequency on one-and two-photon detunings and one-photon Rabi frequencies in a realistic multi-level Cesium atom system. We find that to obtain an atom state flopping efficiency of 0.99 the Raman laser power fluctuation should be controlled to be smaller than 3.2%. We also report our simple experimental Raman laser system for TPRP of Cesium atom based on a fiber waveguide phase modulator. The phase modulator is driven by a 4.6 GHz microwave source and the two first-order sidebands with a frequency difference of 9.19 GHz are filtered out by a Fabry-Pérot cavity with a finesse of 48. After an amplitude-modulator-based intensity stabilization system, a total power of 73 μupW with a fluctuation of 2.2% within 90 min is obtained. By applying this Raman laser to a single Cesium atom trapped in a micrometer size far-off resonant trap (FORT), we obtain Raman spectra between Cesium “clock states” |6S1/2, F=4, mF=0 and |6S1/2, F=3, mF=0. The discrepancy between the two-photon resonance frequency and the defined clock frequency 9.192631770 GHz is due to the differential Stark shifts by FORT beam and Raman beams as well as the inaccuracy of the microwave source. By varying the Raman pulse length we also show the corresponding Rabi flopping with a rate of 153 kHz, which is consistent with the theoretical calculation. The obtained state transfer efficiency of 0.75 is much smaller than theoretical expectation 0.99, which is mainly limited by the state initialization efficiency. The Raman laser system reported in this paper is simple and reliable to realize and it provides a reliable method to manipulate the Cesium internal state. Moreover it could also be easily extended to other system for quantum manipulation of other species of atom.