Xiao-Gang Wei

Erasure of stored optical information in a Pr3+:Y2SiO5 crystal

We experimentally demonstrate an erasure of stored optical information in a Pr3+:Y2SiO5 crystal by applying an erasing pulse to destroy atomic spin coherence. We observed an erasing efficiency of about 85%. Such an erasing operation of stored optical information may have practical applications in the field of information processing and all-optical network.

Enhanced four-wave mixing by atomic coherence in a Pr3+:Y2SiO5 crystal

We experimentally demonstrate an enhanced four-wave mixing (FWM) based on atomic coherence in a Pr3+:Y2SiO5 crystal. By employing coherent population return and fractional stimulated Raman adiabatic passage to prepare maximum atomic coherence in the crystal, an efficient FWM signal can be generated. By measuring the generated FWM signal, the time-dependent atomic coherence is monitored. Such an enhanced FWM in solids may have practical applications in nonlinear optics and laser spectroscopy.

Optical information transfer between two light channels in a Pr 3+ :Y 2 SiO 5 crystal

We experimentally demonstrate light storage and release in a four-level double-lambda atomic system of a Pr (3+):Y(2)SiO(5) crystal. Based on the technique of light storage, we realize optical information transfer between two light channels. The coherent optical information of a probe pulse stored in the crystal can be selectively released into two different light channels by varying the frequency and propagation direction of the switch-on control field.

Coherence transfer between atomic ground states by the technique of stimulated Raman adiabatic passage

We experimentally and theoretically demonstrate that the atomic coherence can be completely transferred or arbitrarily contributed among the different levels in a four-level atomic (tripod) scheme by a group of coupled pulse sequences. This technique can be applied to the information conversion in slow-light storage, quantum logical gates, and so on, which is based on the atomic coherence effect.

Dark and bright Doppler-free resonances observed in atomic 87Rb vapor

We investigate an inhomogeneously broadened four-level atomic system driven by two strong coherent fields and probed by a weak laser. By carefully adjusting strengths of the driving fields, we can observe a greatly enhanced peak between two dark resonances in the probe absorption spectrum. The enhanced absorption peak will split into two lower ones and then result in a third dark resonance if we gradually weaken one driving field. Ultimately, the whole probe absorption spectrum evolves towards the usual EIT spectrum with only one dark resonance. Based on appropriate numerical calculations and qualitative analysis, we show that the experimental results can be well understood by separately considering the probe absorptions arising from partial atoms with different velocities.

Coherent hole-burning phenomenon in a Doppler broadened three-level Λ-type atomic system

In a Doppler broadened three-level Λ-type atomic system, we investigate the absorption spectrum of a weak probe laser in the presence of a saturating laser and a coupling laser. We find that, in order to observe coherent hole-burnings effectively, the two lower levels should be so well spaced that atomic collisions can be neglected, and the saturating (coupling) laser should counter-propagate (co-propagate) with the probe laser. We also give a qualitative analysis to understand the physical origin of coherent hole-burnings.

Storage and selective release of optical information based on fractional stimulated Raman adiabatic passage in a solid

We demonstrate storage and selective release of a light pulse in a Pr:YSO crystal, which is based on atomic spin coherence created by fractional stimulated Raman adiabatic passage (STIRAP). The fractional STIRAP gives better storage fidelity compared to STIRAP. Selective release of stored optical information and better storage fidelity have practical applications in information processing and all-optical communication.

Slow-light information conversion in a rare-earth-ion-doped solid

We report the experimental observation of a slow-light information conversion via electromagnetically induced transparency (EIT) in a rare-earth-ion-doped solid. Under the EIT-based slow-light regime, by manipulating the spectrum of the control fields, the slowed light pulse is transformed into two different frequency-spatial channels. The pulse shapes and energies in two output channels are further studied. This slow-light information conversion can be used as a controllable frequency-spatial multiplexing of the quantum state of the optical field and will be important in information processing and all-optical networks.

Electro-magnetically induced transparency in a static magnetic field

We investigate both theoretically and experimentally the electro- magnetically induced transparency (EIT) phenomenon of atomic 87Rb at the room temperature with a static magnetic field lifting the degeneracy of all three involved hyperfine levels. Two collinearly propagating and linearly polarized laser fields (a probe field and a coupling field) are used to couple one hyperfine level (the upper level) of the 5P1/2 state to two hyperfine levels (the lower levels) of the 5S1/2 state, respectively. In the case of zero magnetic fields, we observed a deep EIT window with the contrast of about 66%. Here, the EIT window width is limited by both the spontaneous decay rate of the upper level and the coupling field intensity. When a magnetic field parallel to both laser beams is applied, the EIT window is split into three much narrower sub-windows with contrasts of about 32%. If the magnetic field is perpendicular to the laser beams, however, the EIT window is split into four much narrower sub-windows whose contrasts are 32% or 16%. This is because the decomposition of the linearly polarized optical fields strongly depends on the orientation of the used magnetic field. The underlying physics is that, in the limit of a weak probe field, an ideal degenerate three-level system can be split into three or four sets of independent three-level systems by a magnetic field due to the lifting of magnetic sublevels of the involved hyperfine levels. In this paper the absorption spectra corresponding to different magnetic field directions are clearly shown and compared. And a straightforward but effective theoretical method for analyzing the experimental results is put forward. Our theoretical calculations are in good agreement with the experimental results.