Xiaomin Feng

Power broadening of electromagnetically induced transparence resonance

The width of an electromagnetically induced transparency (EIT) resonance is studied theoretically for an ideal three-level system in a L-type configuration. The optical Bloch equations are solved and the power broadening behavior of the EIT resonance is studied as a function of both couple and probe laser intensities over a broad range. It is shown that at relative low couple laser intensity there is a quadratic dependence of the EIT width on the couple laser Rabi frequency and at large couple laser intensity the EIT resonance evolve into the well known dynamic Stark splitting and its width has a linear dependence on the couple Rabi frequency. The dependence of the EIT width on the probe laser intensity shows different characteristics with the dependence on the couple laser intensity. Furthermore, the probe laser causes saturation and this is also discussed in this paper.

Control an electromagnetically induced transparence feature with a microwave field

In this paper we present a theoretical study of the effect of a microwave field on an EIT feature. The EIT feature is associated with the well-known three-level Λ type configuration where a pump and probe laser field couples two separate optical transitions. In addition to these two laser fields, there is a microwave field which drives one of the two lower levels of the Λ type three-level system to another hyperfine level. The EIT feature is studied as a function of microwave field frequency and intensity. Our results show that the presence of a microwave field can dramatically modify the EIT feature. When microwave is resonant with the hyperfine transition, the EIT feature can be split into two EIT features. When it is off resonant with the hyperfine transition, it causes a frequency shift of the EIT feature, reminiscent of the well-known light shift effect.

Phase control of linewidth of electromagnetically induced transparency coupled by double fields

The effect of the relative phase on the spectral linewidth of electromagnetically induced transparency is studied in a Λ-type three-level configuration coupled by double coupling fields and the result is presented in this paper. We show that the relative phase between the double coupling fields has a great degree of influence on the spectral width of electromagnetically induced transparency window. The linewidth can be controlled by changing the relative phase. Particularly, as the double coupling fields have opposite phases, the linewidth of EIT window can be extremely narrow distinctly.

Effect of the Bloch-Siegert Shift in a Strongly Driven Transition: High-Order Autler-Townes Doublets

The effect of the Bloch-Siegert shift on a strongly driven transition is further investigated in a V-shaped three-level configuration. Under the condition of taking into account the counter-rotating component, the absorption profiles of the probe field is dominated by a series of doublets, including well-known Autler-Townes doublet and its high-order resonances. The dependence of properties of the secondary Autler-Townes doublet on the driving Rabi intensity is diccussed in this paper.

Optical switching property of electromagnetically induced transparency in a Λ system

In this paper we study the coherent transient property of a Λ-three-level system (Ωd = 0) and a quasi- Λ -four-level system (Ωd>0). Optical switching of the probe field can be achieved by applying a pulsed coupling field or rf field. In Λ -shaped three-level system, when the coupling field was switched on, there is a almost total transparency of the probe field and the time required for the absorption changing from 90% to 10% of the maximum absorption is 2.9Γ0 (Γ0 is spontaneous emission lifetime). When the coupling field was switched off, there is an initial increase of the probe field absorption and then gradually evolves to the maximum of absorption of the two-level absorption, the time required for the absorption of the system changing from 10% to 90% is 4.2Γ0. In four-level system, where rf driving field is used as switching field, to achieve the same depth of the optical switching, the time of the optical switching is 2.5Γ0 and 6.1Γ0, respectively. The results show that with the same depth of the optical switching, the switch-on time of the four-level system is shorter than that of the three-level system, while the switch-off time of the four-level system is longer. The depth of the optical switching of the four-level system was much larger than that of the three-level system, where the depth of the optical switching of the latter is merely 14.8% of that of the former. The speed of optical switching of the two systems can be increased by the increase of Rabi frequency of coupling field or rf field.

Quantum interference in a Λ system using a low frequency driving field

We investigate the quantum interference effects in a cyclic three-level system with a microwave field driving transition between two low levels. By solving the relative density matrix equations of motion, we obtain the absorption profile of the probe field and identify the conditions under which gain may develop. We demonstrate numerically that the absorption line shape depends on the ratio of the intensities of coupling and driving microwave field. When the intensity of coupling field is much weaker than that of driving field, there is a multi-EITs in the probe absorption spectrum. However, if the intensity of both fields is strong, amplification without inversion occurs in different regime of probe frequency. In addition, we predict that larger amplification is obtained when the coupling field is detuned from exact resonance.