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Based on the principle of quantum coherence and quantum spatial positioning,the experimental scheme of the quantum spatial positioning is designed.The spectrum characteristics of the entanglement photons with spontaneous type-II parametric down-conversion pumped by a broadband frequency pulse laser are discussed.The characteristics of the second-order coherent function and the impact of the phase matching conditions on the quantum spatial positioning are analyzed.It is shown that awith the increase of the pump band-width,the coherence of entangled biphoton is diminished,and the measuring accuracy of the quantum spatial positioning is also reduced.

A theoretical research on the variation of the absorption and dispersion profiles and population distribution of each level in a ladder-four-level system driven by two coherent fields has been made. Whether the variation occurs or not depends on the effect of quantum interference, the detuning of the upper coherent field and the separation of the two intermediate levels. A dressed-state analysis is introduced to explain the numerical results.

We report on an experimental observation of constructive quantum interference between two atomic transition pathways 3P1/2-5S (or 4D) and 3P3/2-5S (or 4D) via equal-frequency hybrid excitation and collision-aided radiative excitation in an Na2-Na system. Through the special excitation processes, constructive quantum interference is realized for a Λ-type quantum-beat configuration with a widely-spaced doublet (about 17 cm-1) in the excited sodium atom driven by one laser. The dependences of quantum interference on the argon buffer gas pressure and sample temperature are also examined.

The redox potential of a class of donor-acceptor-donor (D-A-D) molecules, bis(5-substituent-2,3,3,-trimethyl-indolenium-2-ylidene)squaraines (Sq 1-8), were determined. All the dyes exhibit two reversible oxidation potentials in methanol. C-5 substituents at the indolenium moieties exert a small effect on the first oxidation potential, and the substituent effect is attributed to the inductive parameters. The frontier orbital energy levels were calculated by the AM1-SCF method. A good linear relationship between the highest occupied molecular orbital energy level and the first oxidation potential was found. (C) 1999 Elsevier Science Ltd. All rights reserved.

A novel and high resolution method for measuring quantum states with incoherent light in the time-domain is presented. Taking Autler-Townes effect as an example, the physical process and the evolution rule during measurement are discussed by an explicit analytical formulation in detail; and the influence of measuring process on the quantum state is disclosed. With this method, very small splitting of the energy-level and large energy-level space can be measured readily at the same time, while the transverse relaxation rate of the system can be obtained directly by checking the decay time of the signal. Compared with the characteristics of the measuring methods between the time-domain and frequency-domain, we found that the measuring quantum states with incoherent light in the time-domain is robust and valid for disclosing information of the quantum state completely.

We present the analytic expressions for different types of quantum interference effects in coherent instantaneous state quantum system, and discuss the behaviors of the optics and quantum interference, respectively. The important role that the geometrical phase plays in quantum interference is analyzed in detail for the first time. It is demonstrated theoretically that the measurement of the geometrical phase can be realized by appropriately choosing the pulse area of the pump field. The valid control of the quantum interference is achieved by manipulating the chirped pump field.

It is realized that coherent population trapping (CPT) and electromagnetically induced transparency (EIT) are modulated by coherent phase modulation in a Vtype atomic system excited by delaytime laser pulses; the modulation period can reach femtosecond order if the proper energy levels are selected. The relation between the delaytime laser pulse and the population of each energy level are investigated by the numerical and analytical solutions. The characteristic and regularity of population modulated by laser fields phase are obtained as well. Utilizing this mechanism, one can get the quantum switch,of which the modulation period can get to femtosecond order.

In this paper, we study the effects of Rabi frequencies and multi-path radiation on the electromagnetically induced transparency (EIT) and the inversionless gain in a ladder- four-level system driven by two-coherent fields- The Rabi frequencies of the field-driven transition from the upper level to middle levels play an important role for the realization of the ultra-narrow EIT and inversionless gain- Different excitation mechanism can change the position of the EIT- The action of the spontaneous alignment of the dipole moment is investigated- The explanation for the numerical results is presented using the theory of dressed state