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Physical Review A

Quantum coherence effects in quasidegenerate two-level atomic systems

Yabin Dong, Haihong Wang, Jiangrui Gao, Junxiang Zhang

Published Dec 12, 2006• 8 citations
Publisher

Abstract

The wealth of quantum coherence effects depending on the orientation of external magnetic field, the polarization of coupling and probe lights, and the Rabi frequency of the coupling beam are studied in transition ${F}_{e}=2\ensuremath{\leftrightarrow}{F}_{g}=3$ of Cs ${\mathrm{D}}_{2}$ line. The split of electromagnetically induced transparency (EIT) resonances on two or three resonances determined by the different combination of the polarization of interaction lights and the direction of applied magnetic fields is obtained. The shifting and widening of the EIT resonances with the strength of the magnetic field (i.e., Zeeman splitting in the upper and lower levels) and Rabi frequency of the coupling beam increasing are also discussed. It may develop into the potential application for tunable multichannel optical information storage. On the other hand, an explanation of observed asymmetry of spectra by laser frequency offset from the optical resonance is given with theoretical calculation, which is in good agreement with the experimental results.

DOI
10.1103/physreva.74.063810

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The wealth of quantum coherence effects depending on the orientation of external magnetic field, the polarization of coupling and probe lights, and the Rabi frequency of the coupling beam are studied in transition Fe=2\ensuremath↔Fg=3{F}_{e}=2\ensuremath{\leftrightarrow}{F}_{g}=3Fe​=2\ensuremath↔Fg​=3 of Cs D2{\mathrm{D}}_{2}D2​ line. The split of electromagnetically induced transparency (EIT) resonances on two or three resonances determined by the different combination of the polarization of interaction lights and the direction of applied magnetic fields is obtained. The shifting and widening of the EIT resonances with the strength of the magnetic field (i.e., Zeeman splitting in the upper and lower levels) and Rabi frequency of the coupling beam increasing are also discussed. It may develop into the potential application for tunable multichannel optical information storage. On the other hand, an explanation of observed asymmetry of spectra by laser frequency offset from the optical resonance is given with theoretical calculation, which is in good agreement with the experimental results.
Widening and shifting the EIT windows in a closed transition F e = 2 ↔ F g = 3 driven by linearly polarized coupling lights and probed by circularly polarized lights are observed in Cs vapour. It is shown that by increasing the strength of magnetic field i.e. Zeeman splitting in the upper and lower levels, the electromagnetically induced transparency window is divided into two windows and the EIT maxima are shifted away from the zero detuning. In the contrast, if the strength of the magnetic field is fixed and the Rabi frequency of coupling beam is increased, the two EIT windows become wider, and the gap between the two EIT windows becomes smaller and smaller. These effects are also theoretically discussed and they are qualitatively in agreement with the theoretical results.
We have theoretically and experimentally studied the quantum coherence effects of a degenerate transition F g = 3↔ F e = 2 system interacting with a weak linearly polarized (with σ ± components) probe light and a strong linearly polarized (with σ ± components) coupling field. Due to the competition between the drive Rabi frequency and the Zeeman splitting, electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) are present at the different values of applied magnetic field in the case where the Zeeman splitting of excited state Δ e is larger than the Zeeman splitting of ground state Δ g (i.e. Δ e >Δ g ).
The polarization spectra of electromagnetically induced transparency (EIT) for Zeeman sublevels in a cascade system with Rydberg state are demonstrated. The magnitude dependence of Rydberg-EIT on the polarizations of probe and coupling laser fields is studied, and shown mainly due to the strengths of relative dipole matrix elements between degenerate Zeeman sublevels. We further investigate the polarization spectra of Rydberg-EIT in the optimal polarization combinations of left-handed and right-handed circularly polarized fields when an external magnetic field is applied. The existence of nondegenerate Zeeman sublevels in an external magnetic field results in the splitting of Rydberg-EIT. The theoretical calculations are very consistent with the experimental spectra.
For a closed transition Fe = 1 ↔ Fg = 2 driven by linearly polarized light and probed by circularly polarized light, quantum coherence effects induced by the Zeeman sublevels belonging to the different states are investigated. When the Zeeman splitting Δe of the excited level is larger than the Zeeman splitting Δg of the ground level, by increasing the drive Raby frequency, only the widening of the electromagnetically induced transparency (EIT) window with positive dispersion is found. In the opposite case, i.e. Δe ≤ Δg, in a moderate drive Rabi frequency, electromagnetically induced absorption with negative dispersion is obtained due to the shifting of the transparency points. Moreover, for the case of Δe ≤ Δg, a transition from subluminal to superluminal light propagation is predicted at the zero pump–probe detuning.
We investigate the quantum coherence effects of a closed transition F e = 1 ↔ F g = 0 driven by transverse linearly polarized light field (with [sgrave] ± components) and probed by another transverse, linearly polarized light field. Owing to the competition of two-photon gain and single-photon absorption, the absorption spectrum is shown as a combination of electromagnetically induced transparency (EIT) and Mollow absorption spectrum (MAS). In the degenerate case, the MAS covers the EIT window at the pump-probe detuning centre. In the magnetic field, two single-photon absorption peaks inside the EIT windows appear when the drive Rabi frequency is smaller than the Zeeman splitting while, when the Rabi frequency is larger than the Zeeman splitting, we find four emission peaks due to the two-photon gain. A transition from positive to negative dispersion is obtained, which means a shift between the subluminal and superluminal group velocities.
We theoretically investigate the optical response of a degenerate four-level Λ\LambdaΛ-type atomic system under the influence of an external magnetic field. The applied magnetic field lifts the degeneracy of the ground sublevels via the Zeeman effect, thereby altering the two-photon resonance conditions for electromagnetically induced transparency (EIT) formation and causing the atomic response to evolve from single-EIT to double-EIT, accompanied by shifts in the EIT positions. Such variations in the EIT positions result in corresponding changes in the dispersion and group index curves, allowing the selection of desired frequency regions for different response regimes. As a result, the system can switch between transparency and absorption, as well as between slow and fast light. These findings highlight the feasibility of controlling light propagation via magnetic field, with potential applications in optical switching and quantum information technologies.