Unbreakable secret communication has been a dream from ancient time. It is quantum physics that gives us hope to turn this wizardly dream into reality. The rapid development of quantum cryptography may put an end to the history of eavesdropping. This will be largely due to the advanced techniques related to single quanta, especially infrared single photons. In this paper, we report on our research works on single-photon control for quantum cryptography, ranging from single-photon generation to single-photon detection and their applications.

We review the developments of the multipole expansion approach in quantum chromodynamics and its applications to hadronic transitions and some radiative decays of heavy quarkonia. Theoretical predictions are compared with updated experimental results.

A Shell-model-like approach suggested to treat the pairing correlations in relativistic mean field theory is introduced, in which the occupancies thus obtained have been iterated back into the densities. The formalism and numerical techniques are given in detail. As examples, the ground state properties and low-lying excited states for Ne isotopes are studied. The results thus obtained are compared with the data available. The binding energies, the odd even staggering, as well as the tendency for the change of the shapes in Ne isotopes are correctly reproduced.

The present theory of atom optics is established mainly on the Schrödinger equations or the matrix mechanics equation. The authors present a new theoretical formulation of atom optics: Feynman s path integral theory. Its advantage is that one can describe the diffraction and interference of atoms passing through slits (or grating), apertures, and standing wave laser field in Earth s gravitational field by using a type of wave function and calculation is simple. For this reason, we derive the wave functions of particles in the following configurations: single slit (and slit with the van der Waals interaction), double slit, N slit, rectangular aperture, circular aperture, the Mach Zehnder-type interferometer, the interferometer with the Raman beams, the Sagnac effect, the Aharonov Casher effect, the Kapitza Dirac diffraction effect, and the Aharonov Bohm effect. The authors give a wave function of the state of particles on the screen in abovementioned configurations. Our formulas show good agreement with present experimental measurements.

In this review article, we discuss both experimentally and theoretically the second-order double-slit interference for a thermal light source which is random in transverse propagating direction. We show that when the bandwidth of the noise spectrum is increased, the first-order interference pattern disappears while the sub-wavelength pattern fringe emerges in the intensity correlation measurement. Our theoretical description, which is carried out in contrast with coherent light and two-photon state sources, demonstrates that this effect can be explained in accordance with the Hanbury Brown and Twiss experiment.

Electron plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in quartz, fused silica, K9 glass, and Soda Lime glass was investigated by pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging have been used to determine plasma density, relaxation time, and electron collision time in the conduction band. In these materials, the electron collision time is about several femtoseconds when the electron density is in the 10¹⁹cm^-3 range. The electron relaxation processes are different: lifetime is about 170 fs in pure quartz and fused silica, and about 100 ps in K9 and Soda Lime glass. The modified electron band by doped ions is regarded to be responsible for the difference of decay time in these materials.

One- or quasi one-dimensional zinc oxide nanostructures possess plenty of morphologies. Only by controlling the gas flow rates, and partial pressures of argon, oxygen and zinc vapor, can various types of high-quality ZnO nanomaterials (such as wires, belts, arrays, saws or combs, tetraleg rods, nails, and pins) be synthesized through pure zinc powder evaporation without a catalyst at the temperature range of 600 700?C. In this study, deposited nanostructures were characterized by means of scanning electron microscopy, X-ray diffraction and high-resolution transmission electron microscopy. The authors propose and discuss the growth mechanisms of various ZnO. In addition, properties of room temperature photoluminescence and field emission of several typical ZnO nanostructures are measured and investigated.

This paper summarizes our recent work on the application of high static magnetic fields to the austenite-to-ferrite transformation and the tempering processes in hot-rolled 42CrMo steel. The thermodynamic and kinetic effects of the high magnetic fields on austenite decomposition and the influences of the high magnetic field on carbide precipitation and the matrix recovery during high-and low-temperature tempering are briefly outlined. Insight into these aspects may provide better understanding of the effects of high magnetic fields on diffusional phase transformations and is of both theoretical significance and technical interest.

A very effective tool, namely, the analytical expression of the fractional parentage coefficients (FPC), is introduced in this paper to deal with the total spin states of N-body spinor bosonic systems, where N is supposed to be large and the spin of each boson is one. In particular, the analytical forms of the one-body and two-body FPC for the total spin states with {N} and {N-1,1} permutation symmetries have been derived. These coefficients facilitate greatly the calculation of related matrix elements, and they can be used even in the case of N→∞. They appear as a powerful tool for the establishment of an improved theory of spinor Bose Einstein condensation, where the eigenstates have the total spin S and its Z-component being both conserved.

Because the rates of quantum key distribution systems are too low, the interleaving technique and interpolation technique are used to extend the capacity of the quantum key warehouse to increase the quantum key rates of quantum secure communication systems. The simulation shows that the interleaving technique and interpolation technique can extend random sequences and that their randomness are invariable. The correlative theory and technique of digital signal processing is an effective method of extending the quantum key warehouse.

The ionization potentials and fine structure splittings of 1s²nl (l = s, p, and d; n"d9) states for lithium-like V²⁰⁺ ion are calculated by using the full-core plus correlation (FCPC) method. The quantum defects of these three Rydberg series are determined according to the single-channel quantum defect theory (QDT). The energies of any highly excited states with n"e10 for these series can be reliably predicted using the quantum defects that are function of energy. The dipole oscillator strengths for the 1s²2s 1s²np and 1s²2p 1s²nd (n"d9) transitions of V²⁰⁺ ion are calculated with the energies and FCPC wave functions obtained above. Combining the QDT with the discrete oscillator strengths, the discrete oscillator strengths for the transitions from the given initial state to highly excited states (n"e10) and the oscillator strength density corresponding to the bound-free transitions are obtained.

A method of fabricating dual-wavelength fiber Bragg grating with a uniform phase mask is demonstrated. Theoretical analysis and numerical simulation using Matrix method are given. The moving exposing technique is adopted. Good control over the grating s reflectivity and the separation of the two Bragg wavelengths is enabled by adjusting the stretch, the length of the grating, and the exposure. A grating with two equal transmission peaks of 19.5 dB is obtained by using this method, and the separation of the two Bragg wavelengths is 0.78 nm.

The Raman spectra of unintentionally doped gallium nitride (GaN) and Mg-doped GaN films were investigated and compared at room temperature and low temperature. The differences of E₂ and A₁(LO) mode in two samples are discussed. Stress relaation is observed in Mg-doped GaN, and it is suggested that Mg-induced misfit dislocation and electron phonon interaction are the possible origins. A peak at 247 cm^-1 is observed in both the Raman spectra of GaN and Mg-doped GaN. Temperature-dependent Raman scattering experiment of Mgdoped GaN shows the frequency and intensity changes of this peak with temperature. This peak is attributed to the defect-induced vibrational mode.

Superconducting MgB₂ thick film has been prepared via hybrid physical chemical vapor deposition method on Al₂O₃ (0001) substrate by using B₂H₆ and magnesium ingot as raw materials reacted from 730 to 830?C for 40 min under 20 to 30 kPa. Its thickness is about 40 ?m. The MgB₂ thick film shows T_c (onset) = 39.0 K and Tc (0) = 37.2 K. X-ray diffraction pattern shows that the film grown along (101) direction has small amount of impurities of Mg and MgO. Scanning electron microscopy and energy dispersive X-ray spectroscopy indicated that these impurities existed indeed and were Mg rich. The MgO film was formed on the surface of the MgB₂ thick film to further protect the sample from oxidation. We presented a new mechanism for the formation of the thick film.

During the fabrication of intrinsic Josephson junctions (IJJs) with Bi₂Sr₂CaCu₂O_8+δ (BSCCO) single crystals, the superconductivity of the surface Cu O layer is degraded because of