Guo Yan-Qing

Growth characteristics of amorphous-layer-free nanocrystalline silicon films fabricated by very high frequency PECVD at 250°C

Amorphous-layer-free nanocrystalline silicon films were prepared by a very high frequency plasma enhanced chemical vapor deposition (PECVD) technique using hydrogen-diluted SiH4 at 250°C. The dependence of the crystallinity of the film on the hydrogen dilution ratio and the film thickness was investigated. Raman spectra show that the thickness of the initial amorphous incubation layer on silicon oxide gradually decreases with increasing hydrogen dilution ratio. High-resolution transmission electron microscopy reveals that the initial amorphous incubation layer can be completely eliminated at a hydrogen dilution ratio of 98%, which is lower than that needed for the growth of amorphous-layer-free nanocrystalline silicon using an excitation frequency of 13.56 MHz. More studies on the microstructure evolution of the initial amorphous incubation layer with hydrogen dilution ratios were performed using Fourier-transform infrared spectroscopy. It is suggested that the high hydrogen dilution, as well as the higher plasma excitation frequency, plays an important role in the formation of amorphous-layer-free nanocrystalline silicon films.

Quantum State Transfer among Three Ring-Connected Atoms*

A robust quantum state transfer scheme is discussed for three atoms that are trapped by separated cavities linked via optical fibers in a ring connection. It is shown that, under the effective three-atom Ising model, an arbitrary unknown quantum state can be transferred from one atom to another deterministically via an auxiliary atom with maximum unit fidelity. The only required operation for this scheme is replicating turning on/off the local laser fields applied to the atoms for two steps with time cost . The scheme is insensitive to cavity leakage and atomic position due to the condition Δ ≈ κ g. Another advantage of this scheme is that the cooperative influence of spontaneous emission and operating time error can reduce the time cost for maximum fidelity and thus can speed up the implementation of quantum state transfer.

Remote Generation of Entanglement for Individual Atoms via Optical Fibres

The generation of atomic entanglement is discussed in a system that atoms are trapped in separate cavities which are connected via optical fibres. Two distant atoms can be projected to Bell-state by synchronized turning off of the local laser fields and then performing a single quantum measurement by a distant controller. The distinct advantage of this scheme is that it works in a regime where Δ ≈ κ g, which makes the scheme insensitive to cavity strong leakage. Moreover, the fidelity is not affected by atomic spontaneous emission.The generation of atomic entanglement is discussed in a syst em that atoms are trapped in separate cavities which are connected via optical fibers. Two distant atoms can be projected to Bell-state by synchronized turning off the local laser fields and then performing a single quantum me asur ment by a distant controller. The distinct advantage of this scheme is that it works in a regime that ∆ ≈ κ ≫ g, which makes the scheme insensitive to cavity strong leakage. Moreover, the fidelity is not a ffected by atomic spontaneous emission.

Remote atom entanglement in a fibre-connected three-atom system

An Ising-type atom-atom interaction is obtained in a fibre-connected three-atom system. The interaction is effective when ? ? ?0 ? g. The preparations of remote two-atom and three-atom entanglements governed by this interaction are discussed in a specific parameter region. The overall two-atom entanglement is very small because of the existence of the third atom. However, the three-atom entanglement can reach a maximum very close to 1.

A Position-Dependent Two-Atom Entanglement in Real-Time Cavity QED System

We study a special two-atom entanglement case in assumed cavity QED experiment in which only one atom effectively exchanges a single photon with a cavity mode. We compute two-atom entanglement under position-dependent atomic resonant dipole-dipole interaction (RDDI) for large interatomic separation limit. We show that the RDDI, even that which is much smaller than the maximal atomic Rabi frequency, can induce distinct diatom entanglement. The peak entanglement reaches a maximum when RDDI strength can compare with the Rabi frequency of an atom.