基于磁光阱中~6Li冷原子的真空度测量

2018年第26届国际计量大会召开后,伴随着国际单位制的重新定义,真空量值加速了其量子化进程.在超高/极高真空测量领域,可基于囚禁在磁光阱中的冷原子与背景气体碰撞的损失率以及损失率系数反演真空度.本文从磁光阱中冷原子真空测量的基本原理出发,基于量子散射理论小角近似和冲激近似计算了~6Li冷原子与背景气体碰撞的损失率系数,并利用光缔合法测定了在一定磁场和光场条件下的磁光阱阱深,基于两级磁光阱装置通过拟合冷原子数的衰减曲线精确提取出了碰撞损失率.最后在1×10^-8—5×10^-6 Pa压强范围内将真空反演量值与电离计示数对比,分析了制约测量精度提高的因素并提出了改进措施.     

ν↓型三能级原子系统中Raman跃迁增强的Kerr非线性效应

在理论上研究了ν↓型三能级原子系统Raman跃迁中的线性和非线性极化率．研究表明：Raman跃迁中，如果原子完全被抽运到与控制光作用的基态时，将导致介质对探针光的线性极化率为零，而三阶非线性极化率不为零．通过减小原子两基态间的无辐射衰减速率γ12，可以极大地增强交叉Kerr非线性效应．     

Λ型三能级原子系统中Raman跃迁增强的Kerr非线性效应

在理论上研究了Λ型三能级原子系统Raman跃迁中的线性和非线性极化率.研究表明: Raman 跃迁中，如果原子完全被抽运到与控制光作用的基态时，将导致介质对探针光的线性极化率 为零，而三阶非线性极化率不为零.通过减小原子两基态间的无辐射衰减速率γ_{12，可以极大地增强交叉Kerr非线性效应.}     

Frequency-locked tunable LD laser with a broad bandwidth

Using lock-in amplifer and proportional, integral, and derivative (PID) electric circuit, the frequency of diode laser is stabilized on a highly mechanical stable Fabry-Perot (FP) cavity transmission peak. When the frequency locking system is on, the frequency tunable range of the laser is about 4 GHz around the D1 transition of Rb. The laser frequency tuning is implemented by scanning the FP cavity length. The fluctuation of frequency of the output laser is less than 1 MHz, and the drift of the center frequency is less than 1.5 MHz in 1.5 min. This system has great potential of the application in the experimental investigation of the interaction between light and atoms, especially, for the case of far off the atomic resonance.     

在Λ型三能级原子系统中实现光减速及光存储

在充缓冲气体的87Rb原子样品中, 通过探针光、耦合光与Λ型三能级原子相互作用过程中的量子干涉效应,产生了窄线宽的EIT透明窗口,由此实现了探针光群速度的降低.在最好的实验参数条件下,探针光群速度降低到c/42000.同时,研究了光群速减慢与介质温度、耦合光功率以及单光子频率失谐量之间的关系.在此基础上,通过控制耦合光与探针光的通断,实现了光脉冲在原子蒸汽中的存储与读取.     

~6Li原子跃迁频率和超精细分裂的精密测量

本文实现了可用于锂原子频率精密测量的冷原子系统,获得了大数目的原子样品;利用西西弗斯冷却和速度选择相干布居俘获实现了~6Li的冷原子的灰色黏胶冷却,原子的温度被冷却到多普勒冷却极限以下,达到50μK;利用光学频率梳,实验上测量了D1线的跃迁频率和超精细分裂,测量结果和理论计算相接近,可以和目前最精确的测量相比较.这些测量为进一步的轻质量原子频率的精密测量、α常数以及核半径的精确标定打下了基础.     

Optimized geometry and electronic structure of graphyne-like silicyne nanoribbons

Silicyne, a silicon allotrope, which is closely related to silicene and has graphyne-like structure, is theoretically investigated in this work. Its optimized geometry and electronic band structure are calculated by means of the first-principles frozen-core projector-augmented wave method implemented in the Vienna ab initio simulation package (VASP). We find that the lattice parameter is 9.5, the silicon chain between hexagons is composed of disilynic linkages (-Si≡Si-) rather than cumulative linkages (=Si=Si=), and the binding energy is 3.41 eV per atom. The band structure is calculated by adopting the generalized gradient approximation and hybrid functionals. The band gap produced by the HSE06 functional is 0.73 eV, which is nearly triple that by the generalized gradient approximation of Perdew-Burke-Ernzerhof functional.     

半导体激光器的线宽压窄及频率连续调谐

我们利用共焦F—P腔光学弱反馈技术，实现了单模GaAlAs半导体激光器线宽压窄、频率锁定及连续调谐。其线宽从自由运转时的10MHz被压窄到45kHz，并可将频率锁定于共焦F—P腔。实验证明，在弱反馈情况下，激光器的频率连续调谐范围与共焦FP腔的光强反馈量近似成正比，实现了在铷原子D2线附近1．2GHz的频率连续调谐，     

用于冷原子的高精度磁场锁定系统

磁场调控的Feshbach共振是调控原子间相互作用最常用的基本工具,减小磁场起伏,对于提高超冷原子散射共振的稳定性有着重要意义.本文通过一套分流磁场锁定系统,实现了百高斯磁场下相对不确定度为10^-6量级的磁场锁定,相较于未经锁定时,低频电流噪声得到45 dB以上的抑制.利用本文的锁定方法,~6Li原子团Rabi振荡相干时间提高了9.6倍,有效延长了超冷原子系统的相干时间.同时根据原子的Raman损耗谱标定了磁场均方根噪声,通过选择无相互作用的528 Gs (1 Gs=10^-4 T)处进行检测,磁场均方根噪声抑制到1.2 mGs,相较于未经锁定时,磁场均方根噪声降低16倍,磁场锁定相对不确定度为2.27×10^-6.这样的磁场锁定系统,可以为超冷原子气体提供精确稳定的背景磁场,对延长量子存储寿命、精确调控原子散射、开展凝聚态物理模拟等超冷量子气体实验有重要意义.     

Numerical study on characteristic of two-dimensional metal/dielectric photonic crystals

An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of twodimensional(2D) metal/dielectric photonic crystals.Based on the photonic band structures,the dependence of flat bands and photonic bandgaps on two parameters(dielectric constant and filling factor) are investigated for two types of 2D metal/dielectric(M/D) photonic crystals,hole and cylinder photonic crystals.The simulation results show that band structures are affected greatly by these two parameters.Flat bands and bandgaps can be easily obtained by tuning these parameters and the bandgap width may reach to the maximum at certain parameters.It is worth noting that the hole-type photonic crystals show more bandgaps than the corresponding cylinder ones,and the frequency ranges of bandgaps also depend strongly on these parameters.Besides,the photonic crystals containing metallic medium can obtain more modulation of photonic bands,band gaps,and large effective refractive index,etc.than the dielectric/dielectric ones.According to the numerical results,the needs of optical devices for flat bands and bandgaps can be met by selecting the suitable geometry and material parameters.