基于微波相位补偿的56 km高精度光纤微波频率传递

报道了实验室内56 km光纤微波频率传递的实验研究,在56 km的传递距离上实现了1.8×10^-15/s,4×10^-18/10⁴s的传递稳定度。系统通过环回法比较往返传递的微波信号相位获得链路上的相位扰动量,并实时控制本地发射端的微波发射信号相位实现预补偿。在环回往返传递的不同方向上,系统方案采用不同频率的微波调制信号,这种方法极大避免了光寄生反射效应的影响,同时利用色散补偿光纤改善探测信号相噪等措施,提高了系统的传递稳定度。     

Observation of Autler-Townes Effect in ElectromagneticaUy Induced Transparency

We report an experimental observation of Autler-Townes doublet splitting in electromagnetically induced transparency （EIT） resonance. The splitting is introduced by a coherent microwave field, which perturbs a three-level A-type EIT system through an auxiliary level. The doublet splitting of EIT resonance is demonstrated in two cases, where the microwave field shares a common lower level with coupled or probe transition, respectively. The dependence of doublet splitting on microwave field intensity and detuning is measured. This may provide a feasible way of manipulating the atomic states with both laser and microwave field.     

Photonic generation of RF and microwave signal with relative frequency instability of 10~(-15)

We demonstrate the ultra-stable frequency sources aiming to improve the short-time instability of primary frequency standards. These sources are realized by using photonic generation approach, and composed of ultra-stable lasers, opticalfrequency-combs, optical signal detecting parts, and synthesizers. Preliminary evaluation shows that the sources produce fixed-frequency at 9.54(/9.63) GHz, 10 MHz, and tunable-frequency around 9.192 GHz with relative frequency instability of 10~(-15) for short terms.     

Ground state of rotating ultracold quantum gases with anisotropic spin orbit coupling and concentrically coupled annular potential

Motivated by recent experimental realization of synthetic spin–orbit coupling in neutral quantum gases, we consider the quasi-two-dimensional rotating two-component Bose–Einstein condensates with anisotropic Rashba spin–orbit coupling subject to concentrically coupled annular potential. For experimentally feasible parameters, the rotating condensate exhibits a variety of rich ground state structures by varying the strengths of the spin–orbit coupling and rotational frequency.Moreover, the phase transitions between different ground state phases induced by the anisotropic spin–orbit coupling are obviously different from the isotropic one.     

基于光学时延补偿的50 km光纤微波频率传递

报道了利用50 km光纤实现4.38×10~(-15)@1 s和2.80×10~(-18)@65.5×10~3s稳定度的微波频率传递的实验研究.实验系统采用多普勒噪声消除技术,通过在本地端探测往返传递的微波信号相位获得链路上的相位变化信息,并实时控制光延迟调整机构进行补偿.光延迟控制采用压电陶瓷的快速拉伸和慢速光纤温控联合方式,可实现5 ns和千赫兹带宽的光延迟控制,能够实现光纤噪声的长期高精度补偿.与电相位补偿相比,光延迟补偿受微波泄露的影响相对较小,而微波泄露影响在类似系统难以避免,因此这种方式更利于获得高稳定度的频率传递.此外,系统采用变频往返传递消除光寄生反射效应,以及色散补偿光纤减小因色散引起的调制信号衰减等措施,提高了系统的技术指标.