Wenxian Zhang

Physical mechanisms for the unique optical properties of chalcogen-hyperdoped silicon

A series of fundamental properties from atomic geometry, electronic band structure, optical absorption, to dynamics are systemically studied for the silicon doped with supersaturated chalcogens (S, Se, and Te). The atomic structures in a broad energy range are obtained and distinguished as three classes named the substitutional, interstitial, and quasi-substitutional. Their relative energies varying with the S, Se, and Te samples reveal that the concentration of impurity atoms occupying the substitutional position, which plays an important role in optical absorption, will be different and get progressively higher from S-, Se-, to Te-hyperdoped silicon. Electronic band structures show that for the most atomic geometries the defect-related states do appear into the gap of silicon, and the optical absorption calculations clarify that they are the very origin of the broadband absorption of chalcogen-hyperdoped silicon. Combining the optical absorption properties with the structural transformation from molecular-dynamics simulations, we disclose the micromechanism of annealing-induced reduction of infrared absorptance. Furthermore, we conclude that both the different concentrations of the substitutional doping and structural transformation will lead to the different annealing-induced reduction of infrared absorptance for S-, Se-, and Te-hyperdoped silicon as observed in experiments.

Localization of spin mixing dynamics in a spin-1 Bose-Einstein condensate

We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein condensate by a temporal modulation of spin exchange interaction, which is tunable with optical Feshbach resonance. Adopting techniques from coherent control, we demonstrate the localization and freezing of spin mixing dynamics, and the suppression of the intrinsic dynamic instability and spontaneous spin domain formation in a ferromagnetically interacting condensate of {sup 87}Rb atoms. This work points to a promising scheme for investigating the weak magnetic spin dipole interaction, which is usually masked by the more dominant spin exchange interaction.

Magnetic-field-induced dynamical instabilities in an antiferromagnetic spin-1 Bose-Einstein condensate

We theoretically investigate four types of dynamical instability, in particular the periodic and oscillatory type

Preserving coherent spin and squeezed spin states of a spin-1 Bose-Einstein condensate with rotary echoes

{I}_{O}

Manipulating dipolar and spin-exchange interactions in spin-1 Bose-Einstein condensates

, in an antiferromagnetic spin-1 Bose-Einstein condensate in a nonzero magnetic field, by employing the coupled-mode theory and numerical method. This is in sharp contrast to the dynamical stability of the same system in zero field. Remarkably, a pattern transition from a periodic dynamical instability

Excitation of large-scale delocalized quantum state by local interactions

{I}_{O}

Rebuilding of destroyed spin squeezing in noisy environments

to a uniform one

Heisenberg-scaled magnetometer with dipolar spin-1 condensates

{\mathit{\text{III}}}_{O}

Quantum hydrodynamics and expansion of a strongly interacting Fermi gas

occurs at a critical magnetic field. All four types of dynamical instability and the pattern transition are ready to be detected in

Preserving squeezed spin states of a spin-1 Bose-Einstein condensate with rotary echoes

^{23}\mathrm{Na}