[en] We propose a transformation method that simplifies quantitative analysis in the Λ-type electromagnetically induced transparency (EIT) system containing degenerate Zeeman states. This transformation maps several coupled three-state systems into a simple three-state system. Moreover, we demonstrate that the transformation is an excellent approximation under adiabatic conditions and the calculation results from several coupled systems are in good agreement with those from the simple system. The transformation method is a powerful tool for relevant studies of EIT, slow light, and storage of light

[en] We experimentally demonstrate a low-light-level cross-phase-modulation (XPM) scheme based on the light-storage technique in laser-cooled ⁸⁷Rb atoms. The proposed scheme can achieve a similar phase shift and has the same figure of merit as one using static electromagnetically induced transparency under the constant coupling field. Nevertheless, the phase shift and the energy loss of a probe pulse induced by a signal pulse are neither influenced by the coupling intensity nor by the atomic optical density in the light-storage XPM scheme. This scheme enhances the flexibility of the experiment and makes possible conditional phase shifts on the order of π with single photons

[en] We observed the transient oscillation in the spectra of electromagnetically induced transparency by rapidly sweeping the probe laser frequency. The spectra were measured with laser-cooled ⁸⁷Rb atoms. We show that the amplitude of the transient oscillation decays exponentially at a rate of Ω_c²/2Γ, where Ω_c is the Rabi frequency of the coupling laser and Γ is the spontaneous decay rate of the excited state. Using the transient oscillation, we demonstrate a simple method to determine Ω_c. This method is particularly useful with the low-intensity coupling laser

[en] We have systematically studied the method proposed by Patnaik et al. [Phys. Rev. A 69, 035803 (2004)] that manipulates the retrieval of stored light pulses. The measured probe pulse width of the retrieval is inversely proportional to the intensity of the reading field. We also show that the method does not introduce any phase shift or jump into the retrieved pulses. Our study demonstrates that the distortion at the output of the light storage can be corrected by manipulating the retrieval process and the phase information of the stored pulses can remain intact during the process

[en] We have experimentally studied the transient behaviors of photon switching by quantum interference in laser-cooled ⁸⁷Rb atoms. The experimental results are consistent with theoretical predictions. We show that the rise time of the probe absorption cannot be less than 2/Γ where Γ is the spontaneous decay rate of the excited states. In the low-intensity limit, the rise time is equal to 2Γ/(Ω_c²+Ω_s²) for the scheme used here, where Ω_c and Ω_s are the Rabi frequencies of the coupling and switching fields. A simple picture based on the dark and nondark states is provided to explain these transient behaviors

[en] We study the creation of stationary light pulses (SLPs), i.e., light pulses without motion, based on the effect of electromagnetically induced transparency with two counterpropagating coupling fields in cold atoms. We show that the Raman excitations created by counterpropagating probe and coupling fields prohibit the formation of SLPs in media of cold and stationary atoms such as laser-cooled atom clouds, Bose condensates or color-center crystals. A method is experimentally demonstrated to suppress these Raman excitations and SLPs are realized in laser-cooled atoms. Furthermore, we report the first experimental observation of a bichromatic SLP at wavelengths for which no Bragg grating can be established. Our work advances the understanding of SLPs and opens a new avenue to SLP studies for few-photon nonlinear interactions.

[en] We have experimentally studied the propagation behaviors of light pulses in an electromagnetically induced transparency (EIT) medium. Both phase variation in different parts of a pulse and distortion of the pulse shape are observed. The consistency between the experimental data and theoretical predictions is satisfactory. Our study explains the physical origins of the phase variation and the shape distortion, shows that the phase variation should be taken into consideration in applications utilizing the EIT scheme in which two-photon detuning must exist, and provides better understanding of the propagation behavior of the slow light

[en] We describe a proof-of-principal experiment demonstrating the use of spread spectrum technology at the single photon level. We show how single photons with a prescribed temporal shape, in the presence of interfering noise, may be hidden and recovered.

[en] We model the effects of the atomic thermal motion on the propagation of a light pulse in an electromagnetically induced transparency medium by introducing a set of effectively temperature-dependent parameters, including the Rabi frequency of the coupling field, optical density and relaxation rate of the ground state coherence, into the governing equations. The validity of this effective theory is verified by the close agreement between the theoretical results and the experimental data.

[en] We developed the Adomian's decomposition method to work for the electromagnetically induced transparency (EIT) problem. The method is general and capable to solve the coupled nonlinear partial differential equations for a light pulse passing through a three-level Λ-type coherent medium. This EIT system is described by the coupled Maxwell-Schroedinger equations and optical Bloch equations. In the weak probe field case, the results agree with perturbation solutions and experimental data. In the stronger probe field case while perturbation may fail, our results reproduce experimental data well. With the techniques of spatial and time partitions, we extend the decomposition method that will be versatile for the investigation of the light pulse propagating through a coherent atomic medium