We propose a scheme for two-dimensional sub-half-wavelength atom localization using two lasers with equal frequencies, and obtain the analytical expression of conditional position probability (CPP) using a spontaneous-emission spectrum for a four-level atom which passes through two-dimensional orthogonal standing-wave fields. The quantum interference effect between two decay channels leads to extreme spectral narrowing and quenching of spontaneous emission in some regions of the standing-wave field, which results in the appearance of a high-spatial-resolution localization peak. The two-dimensional sub-half-wavelength atom localization is obtained with high precision and high spatial resolution by adjusting the relative phase and detuning.

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We propose a theoretical scheme in a cold rubidium-87 (87Rb) atomic ensemble with a non-Hermitian optical structure, in which a lopsided optical diffraction grating can be realized just with the combination of single spatially periodic modulation and loop-phase. Parity-time (PT) symmetric and parity-time antisymmetric (APT) modulation can be switched by adjusting different relative phases of the applied beams. Both PT symmetry and PT antisymmetry in our system are robust to the amplitudes of coupling fields, which allows optical response to be modulated precisely without symmetry breaking. Our scheme shows some nontrivial optical properties, such as lopsided diffraction, single-order diffraction, asymmetric Dammam-like diffraction, etc. Our work will benefit the development of versatile non-Hermitian/asymmetric optical devices.

The effect of viscosity and viscosity difference and boundary patterned slip on mixing in a micro mixer has been numerically studied using lattice Boltzmann method (LBM). The slip and no-slip ratio is not constant and varies irregularly, and viscosity is altered by changing the relaxation time in LBE equation. The slip boundary condition is simulated by specular reflection boundary and the no-slip boundary condition is simulated by bounce back boundary. It has been found that it is feasible to optimize the micro mixer design by combining the viscosity effect and boundary patterned ratio altogether.