The optical rectification coefficient in electric-field biased hyperbolic quantum wells was studied. The analytic expression of optical rectification coefficient of this system is derived by means of density matrix approach and the iterative method. Finally, the numerical results were presented for a typical GaAs electric-field biased hyperbolic quantum wells. The results show that the optical rectification coefficient in this system is larger than that in bulk GaAs material and it will change with the change of the parameter a of the quantum well and the applied electric field F.

The wavelength management method was theoretically investigated for the polarizationentangled twin photons in telecommunication band generated by type-Ⅱ quasi-phase-matched (QPM) spontaneous parametric down-conversion (SPDC) in periodically poled lithium niobate (PPLN) crystals. The wavelength of single-color twin photons from degenerate SPDC can be controlled freely through adjusting the QPM grating period or the working temperature. Especially, adjusting the temperature is more convenient since the QPM grating period is hardly changed once the PPLN structure is fabricated. For the two-color twin photons created by nondegenerate SPDC, strict wavelength exchange of the o-polarization and the e-polarization photons can be realized easily only by tuning the working temperature without pump or structure change.

A scheme was proposed to generate the W-type entangled coherent states of three-cavity fields, after comparing the differences between the discrete-variable quantum information and the continuous-variable quantum information and taking into account that coherent states were presently of practical use and readily available. The scheme was based on the degenerate Raman interaction of a A-type three-level atom with a single-mode field. Three identical cavities were in coherent states and three identical atoms shared a W-type entangled state initially. Let the three atoms interact with the three cavity fields respectively, selected a proper interaction time and detected the three atoms after exiting from their respective cavity. Then the three-cavity fields were projected onto a W-type entangled coherent states. During the atom-field interaction the atoms have no probability of being populated in the upper level, then the atomic spontaneous emissions could be neglected. Therefore, the coherence of the system might be better maintained. Based on current cavity quantum electrodynamics technique, the scheme could be realized experimentally. The W-type entangled coherent states generated was expected to be useful in the continuous-variable quantum information processing. The scheme was generalized to prepare the W-type entangled coherent states of n-cavity fields (n＞3).