Symmetry restoration and quantumness reestablishment

A realistic quantum many-body system, characterized by a generic microscopic Hamiltonian, is accessible only through approximation methods. The mean field theories, as the simplest practices of approximation methods, commonly serve as a powerful tool, but unfortunately often violate the symmetry of the Hamiltonian. The conventional BCS theory, as an excellent mean field approach, violates the particle number conservation and completely erases quantumness characterized by concurrence and quantum discord between different modes. We restore the symmetry by using the projected BCS theory and the exact numerical solution and find that the lost quantumness is synchronously reestablished. We show that while entanglement remains unchanged with the particle numbers, quantum discord behaves as an extensive quantity with respect to the system size. Surprisingly, discord is hardly dependent on the interaction strengths. The new feature of discord offers promising applications in modern quantum technologies.

Broadband optical amplification near 1300 nm in bismuth-doped germanate glass

In this paper, we present the broadband optical amplification in bismuth-doped germanate glass, at the second telecommunication window when excited with 808 nm and 980 nm laser diodes, respectively. The amplification range is from 1272 nm to 1348 nm wavelength, which is within the O-band of silica fiber communication. This bismuth-doped glass can be used as ultra broadband amplification material for wavelength-division-multiplexing (WDM) at the second telecommunication window.

Mg，Ti共掺Al2O3透明多晶陶瓷光谱性能研究

Transparent polycrystalline MgO and TiO2 codoped Al2O3 ceramics were fabricated by conventional solid-state pressureless processing. The absorption, emission and excitation spectra of ( Mg, Ti : Al2O3 ceramics were measured. Owing to charge compensation of Mg2+, only UV absorption around 250nm was observed due to O2- -> Ti4+ charge transfer transitions (CT) when Ti content was low. As a result, the emission peaks of isolated Ti4+ ion located at 280-290nm and 410-420nm were observed. Besides absorption peak of V, ion, the characteristic absorption peak of V, ion centered at 490nm was observed in Mg, Ti) : Al2O3 ceramics when Ti content was high. The emission spectra of Ti3+, ion in polycrystalline Al2O3 ceramics coincide with that of Ti: Al2O3 single crystal.

Cr4+在Al2O3多晶体中的光谱性能研究

Transparent polycrystalline Cr:Al2O3 ceramics were synthesized by conventional pressureless synthesis processing. The absorption and emission spectra of Cr:Al2O3 ceramics specimens before and after annealing were measured at room temperature. It was discovered that the emission spectra of Cr4+ in Al2O3 octahedral coordination site is in infrared wavelength range of 1100-1600 nm. The emission peak of Cr4+ is centered at 1223 nm, which is similar to that of Cr4+ in tetrahedral site. Al2O3 has smaller lattice constant, resulting in the larger crystal field strength, so there is a blue shift in the peak of Cr4+:Al2O3 ceramics compared to those of other Cr4+-doped crystals. And the emission band is much narrower with full width at half maximum Delta lambda 37 nm.

Effect of La2O3 on microstructure and transmittance of transparent alumina ceramics

Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H-2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical densities (T. D.) with increasing content of La2O3. With increasing holding time during sintering, much less pores and larger grains were found in the sintered alumina samples. Higher transmittance was achieved in alumina codoped with MgO and La2O3 as compared with that doped with MgO only. The total-transmittance of alumina sample is up to 86% at a wavelength range of 300 - 800 nm.