To clarify the contribution of oxygen vacancies to room-temperature ferromagnetism (RTFM) in cobalt doped TiO₂ (Co-TiO₂), and in order to obtain the high level of magnetization suitable for spintronic devices, in this work, Co-TiO₂ nanoparticles are prepared via the sol–gel route, followed by vacuum annealing for different durations, and the influence of vacuum annealing duration on the structure and room-temperature magnetism of the compounds is examined. The results reveal that with an increase in annealing duration, the concentration of oxygen vacancies rises steadily, while the saturation magnetization (M_s) shows an initial gradual increase, followed by a sharp decline, and even disappearance. The maximum M_s is as high as 1.19 emu/g, which is promising with respect to the development of spintronic devices. Further analysis reveals that oxygen vacancies, modulated by annealing duration, play a critical role in tuning room-temperature magnetism. An appropriate concentration of oxygen vacancies is beneficial in terms of promoting RTFM in Co-TiO₂. However, excessive oxygen vacancies will result in a negative impact on RTFM, due to antiferromagnetic superexchange interactions originating from nearest-neighbor Co²⁺ ions.

A mixed light field generated from a two-level atomic ensemble can be used for two-photon interference. In this mixed light field, correlated paired photons generated from a four-wave mixing process provide a signal of two-photon interference, while Rayleigh scattered photons of the pump laser provide a stable reference to calibrate the normalized second-order correlation function. We demonstrate two-photon interference using the Hong–Ou–Mandel and Hanbury Brown–Twiss interferometers. A direct quantitative comparison between theoretical predictions and experimental data is performed under perturbed experimental conditions, which reveal this kind of light source has potential application for quantum metrology.

We report on the observation of the highly forbidden S10–P30 optical clock transition in laser-cooled Hg199 atoms. More than 95% depletion of cold Hg199 atoms is detected in the magneto-optical trap. Using the free-of-field detection method, the AC Stark shift from the cooling laser is removed from the in-field spectroscopy. At low-power clock laser pumping, the linewidth of the clock spectroscopy is approximately 450 kHz (full width at half-maximum), which corresponds to a Doppler broadening at the atom temperature of 60 μK. We determine the S10–P30 transition frequency to be 1,128,575,290.819(14) MHz by referencing with a hydrogen maser and measuring with a fiber optical frequency comb. Moreover, a weak Doppler-free signal is observed.

We present a simple method to measure the spatial coherence of hard x-ray beams. Based on the convolution of Gaussian functions, we analyze the diffraction patterns of a grating irradiated by partially coherent hard x rays with a constrained beam diameter. The spatial coherence properties of an x-ray beam are obtained from the width of the diffraction peaks with high accuracy. The results of experiments conducted by combining a pinhole with a grating show a good agreement with our calculation using the Gaussian–Schell model.

We report the recent progress of our pulsed optically pumped (POP) vapor cell rubidium clock with dispersive detection. A new compact physics package is made. A rubidium cell with a high precision buffer gases mixing ratio is obtained, and the temperature controlling system is renovated to reduce fractional frequency sensitivity to temperature variation. The resolution of the servo control voltage is also optimized. With these improvements, a clock frequency stability of 3.53×10 13 at 1 s is obtained, and a fractional frequency stability of 4.91×10 15 is achieved at an average time of τ=2000 s.

We investigate the spin dynamics, starting from the initial band-insulating state, of fermionic high-spin atoms in optical superlattices. Through numerical simulations and analytical calculations, we determine the time evolution behavior of the system. When the spin-changing strength and tunneling strength are comparable, the spin dynamics feature a spin-changing oscillation with the amplitude modulated by the superexchange interaction. When the double-well potential is very shallow, the spin dynamics feature a simple harmonic oscillation with the oscillation frequencies related only to the spin-changing strength, which can be properly explained with the perturbation model.