Chun-Liang Wang

Observation of the fluorescence spectrum for a driven cascade model system in atomic beam

We experimentally study the resonance fluorescence from an excited two-level atom when the atomic upper level is coupled by a nonresonant field to a higher-lying state in a rubidium atomic beam. The heights, widths and positions of the fluorescence peaks can be controlled by modifying the detuning of the auxiliary field. We explain the observed spectrum with the transition properties of the dressed states generated by the coupling of the two laser fields. We also attribute the line narrowing to the effects of Spontaneously Generated Coherence between the close-lying levels in the dressed state picture generated by the auxiliary field. And the corresponding spectrum can be viewed as the evidence of Spontaneously Generated Coherence. The experimental results agree well with calculations based on the density-matrix equations.

Goos–Hänchen shift of the reflected beam in a standing-wave coupled electromagnetically induced transparency system

The Goos–Hanchen shift of the reflected beam in a standing-wave coupled electromagnetically induced transparency medium is investigated. We adopt the three-level Λ system as a model of Rb87 atomic media. Under the influence of two counterpropagating coupling fields, the incident beam is converted into a reflected one, with the Goos–Hanchen shift. We briefly discuss the rules for obtaining efficient reflection in such an atomic system, and carefully investigate the Goos–Hanchen shift and its dependence on the beam width of the incident field. Both the cases with and without Doppler broadening are considered. In order to provide a clearer physical picture on the large shift that could be realized, the concept of penetration depth is used to analyze the shift phenomenologically.

Creation and Transfer of Coherence via Technique of Stimulated Raman Adiabatic Passage in Triple Quantum Dots

We propose a scheme for creation and transfer of coherence among ground state and indirect exciton states of triple quantum dots via the technique of stimulated Raman adiabatic passage. Compared with the traditional stimulated Raman adiabatic passage, the Stokes laser pulse is replaced by the tunneling pulse, which can be controlled by the externally applied voltages. By varying the amplitudes and sequences of the pump and tunneling pulses, a complete coherence transfer or an equal coherence distribution among multiple states can be obtained. The investigations can provide further insight for the experimental development of controllable coherence transfer in semiconductor structure and may have potential applications in quantum information processing.

Control of coherence transfer via tunneling in quadruple and multiple quantum dots

Transfer and manipulation of coherence among the ground state and indirect exciton states via tunneling in quadruple and multiple quantum dots is analyzed. By applying suitable amplitudes and sequences of the pump and tunneling pulses, a complete transfer of coherence or an arbitrary distribution of coherence of multiple states can be realized. The method, which is an adiabatic passage process, is different from previous works on quantum dot molecules in the way that the population can transfer from the ground state to the indirect exciton states without populating the direct exciton state, and thus no spontaneous emission occurs. This investigation can provide further insight to help the experimental development of coherence transfer in semiconductor structures, and may have potential applications in quantum information processing.

Observation of linewidth narrowing due to a spontaneously generated coherence effect

We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields. We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the latter being a system that exhibits spontaneously generated coherence and can display ultrasharp spectral lines. We find a suitable energy scheme in a Rb-85 atom and experimentally observe the narrowing of the central peak in a rubidium atomic beam. The corresponding spectrum can convincingly demonstrate the existence of spontaneously generated coherence.