Hanzhuang Zhang

Observation of light amplification without population inversion in sodium

Abstract We discuss the results of experiments on the amplification of visible electromagnetic radiation without population inversion using sodium vapor as the active medium. The main result of this work is the amplification of a weak probe beam at a wavelength of 589.0 nm in the presence of an intense, pulsed, coherent driving field at 589.6 nm.

Inversionless light amplification in sodium

Abstract Light amplification without population inversion in sodium vapor is reported. The result of this work is the amplification of a weak probe beam at a wavelength of 589.0 nm when the atoms are driven coherently by a long pulse at 589.6 nm, and the amplification of a weak probe beam at 589.6 nm when the atoms are driven coherently at 589.0 nm. The population contributions in the upper and lower lasing levels are calculated through the absorption spectra.

Response to modulation of parameters in the vibro-rotational model for a CO2 laser

The response of a single mode CO2 laser to modulation of pump, loss, and cavity length based on the vibro-rotational model is analysed and compared with similar analyses for the two-level rate equation model for laser action.

Fidelity of structured amplitude-damping channels

We study the properties of the fidelity of one-qubit operations in amplitude damping channels and reveal their properties as a function of coupling to the photonic crystal environment. We show that there is a direct connection between the information fidelity and the detuning of the atomic frequency from the photonic band gap (PBG). When the atomic transition frequency is far inside the band gap, the time evolution of the fidelity maintains asymptotically a steady-state value and can be controlled by the controllable PBG environment. We finally study the entanglement fidelity of the two-qubit system in this quantum channel. The theoretical results could be applied to the implementation of linear-optical and solid-state quantum information processing in nanostructured materials.

Influences of Microscopic Parameters of Tripod Like Chiral Molecules on the First Zero-Frequency Hyperpolarizabilities

In this study, we derived explicitly the zero-frequency first hyperpolarizabilities of tripod like chiral molecules based on a three-coupled-oscillator model and determined the relations of the zero-frequency first hyperpolarizabilities with molecular structure, molecular chirality and the wavelength of incident light. Furthermore, we also simulated numerically the influences of microscopic parameters of chiral molecules and the wavelength of incident light on the first zero-frequency hyperpolarizabilities. We observed fact that the influences of microscopic parameters of chiral molecules on zero-frequency first hyperpolarizabilities is different by using different chiral molecular microscopic parameters such as bond angle and molecular chirality. Furthermore, the influences of microscopic molecular parameters on the first zero-frequency hyperpolarizabilities can also help to comprehend nonlinear optical mechanism of chiral molecules.

Quantum speedup of an atom coupled to a photonic-band-gap reservoir

For a model of an atom embedded in a photonic-band-gap reservoir, it was found that the speedup of quantum evolution is subject to the atomic frequency changes. In this work, we propose different points of view on speeding up the evolution. We show that the atomic embedded position, the width of the band gap and the defect mode also play an important role in accelerating the evolution. By changing the embedded position of the atom and the coupling strength with the defect mode, the speedup region lies even outside the band-gap region, where the non-Markovian effect is weak. The mechanism for the speedup is due to the interplay of atomic excited population and the non-Markovianity. The feasible experimental system composed of quantum dots in the photonic crystal is discussed. These results provide new degree of freedoms to depress the quantum speed limit time in photonic crystals.

Radiation amplification without population inversion: a four level model

We report experimental results of radiation amplification without population inversion in sodium according to a four-level model.