Demonstration of a cold atom beam splitter on atom chip

We report an experimental demonstration of a new scheme to split cold atoms on an atom chip. The atom chip consists of a U-wire and a Z-wire. The cold atom cloud is initially loaded and prepared in the Z-trap, which is split into two separate parts by switching on the current of the U-wire. The two separate atom clouds have a distance more than one millimeter apart from each other and show almost symmetrical profiles, corresponding to about a 50/50 splitting ratio.

Parametric resonance and cooling on an atom chip

This paper observes the parametric excitation on atom chip by measuring the trap loss when applying a parametric modulation. By modulating the current in chip wires, it modulates not only the trap frequency but also the trap position. It shows that the strongest resonance occurs when the modulation frequency equals to the trap frequency. The resonance amplitude increases exponentially with modulation depth. Because the Z-trap is an anharmonic trap, there exists energy selective excitation which would cause parametric cooling. We confirm this effect by observing the temperature of atom cloud dropping.

Single layer atom chip for magnetically trapping one-dimensional array of ultracold atoms

We propose a wire configuration to create a one-dimensional （1D） array of magnetic microtraps for trapping ultracold atoms. The configuration is formed by replacing the central part of the Z-wire pattern with a zigzag wire. We simulate the performance of this pattern by the finite element method which can take both the width and depth of the wire into consideration. The result of simulation shows that this configuration can create magnetic microtraps which can be separated and combined by changing bias magnetic field. We manage to split Z-wire trap and prove that similar result can occur for the new wire configuration. The fabrication processes of the atom chip are also introduced. Finally we discuss the loading method.

Dynamic splitting and merging of an atom cloud on an atom chip

Chip-based atom interferometers bring together the advantages of atom chips and Bose-Einstein condensates. Their central prerequisite is that a condensate can be coherently split into two halves with a determined relative phase. This paper demonstrates the dynamical splitting and merging of an atom cloud with two U-wires on an atom chip. Symmetrical and asymmetrical splittings are realized by applying a bias field with different directions and magnitudes. The trajectories of the splitting are consistent with theoretical calculations. The atom chip is a good candidate for constructing an atom interferometer.

Bose-Einstein condensation on an atom chip

This paper reports an experiment of creating Bose-Einstein condensate （BEC） on an atom chip. The chip-based Z-wire current with a homogeneous bias magnetic field creates a tight magnetic trap, which allows for a fast production of BEC. After a 4.17-s forced radio frequency evaporative cooling, a condensate with about 3000 atoms appears. The transition temperature is about 300 nK. This compact system is quite robust, allowing for versatile extensions and further studying of BEC.

Microwave coherent manipulation of cold atoms in optically induced fictitious magnetic traps on an atom chip

We propose a novel on-chip platform for controlling and manipulating cold atoms precisely and coherently. The scheme is achieved by producing optically induced fictitious magnetic traps（OFMTs） with 790 nm（for -（87）Rb） circularly polarized laser beams and state-dependent potentials simultaneously for two internal atomic states with microwave coplanar waveguides. We carry out numerical calculations and simulations for controlled collisional interactions between OFMTs and addressable single atoms＇ manipulation on our designed hybrid atom chips. The results show that our proposed platform is feasible and flexible, which has wide applications including collisional dynamics investigation, entanglement generation,and scalable quantum gates implementation.

Direct loading of atoms from a macroscopic quadrupole magnetic trap into a microchip trap

We demonstrate the direct loading of cold atoms into a microchip 2-mm Z-trap, where the evaporative cooling can be performed efficiently, from a macroscopic quadrupole magnetic trap with a high loading efficiency. The macroscopic quadrupole magnetic trap potential is designed to be moveable by controlling the currents of the two pairs of anti-Helrnholtz coils. The cold atoms are initially prepared in a standard six-beam magneto-optical trap and loaded into the macroscopic quadrupole magnetic trap, and then transported to the atom chip surface by moving the macroscopic trap potential. By means of a three-dimensional absorption imaging system, we are able to optimize the position alignment of the atom cloud in the macroscopic trap and the microchip Z-shaped wire. Consequently, with a proper magnetic transfer scheme, we load the cold atoms into the microchip Z-trap directly and efficiently. The loading efficiency is measured to be about 50%. This approach can be used to generate appropriate ultracold atoms sources, for example, for a magnetically guided atom interferometer based on atom chip.

Production and guidance of pulsed atomic beams on chip

We demonstrated two experimental methods of producing and guiding pulsed atomic beams on chip. One is to trap atoms first in a U-type magneto-optical trap on the chip, then transfer them to the magnetic guide field and push them simultaneously by a continuous force from the power imbalance of the magneto-optical trap laser beams hence the pulsed cold atom beams are produced and move along the magnetic guide to the destination. The other is to trap atoms directly by a H-type magneto-optical trap, then push them to make them move along the magnetic guide field, thus high rate cold atom beams can be produced and guided on the chip.

Review of chip-scale atomic clocks based on coherent population trapping

Research on chip-scale atomic clocks （CSACs） based on coherent population trapping （CPT） is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the re- liability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance＇s collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research.

Integrated physics package of a chip-scale atomic clock

The physics package of a chip-scale atomic clock （CSAC） has been successfully realized by integrating vertical cavity surface emitting laser （VCSEL）, neutral density （ND） filter, λ/4 wave plate, 87Rb vapor cell, photodiode （PD）, and magnetic coil into a cuboid metal package with a volume of about 2.8 cm3. In this physics package, the critical component, 87Rb vapor cell, is batch-fabricated based on MEMS technology and in-situ chemical reaction method. Pt heater and thermistors are integrated in the physics package. A PTFE pillar is used to support the optical elements in the physics package, in order to reduce the power dissipation. The optical absorption spectrum of 87Rb D1 line and the microwave frequency correction signal are successfully observed while connecting the package with the servo circuit system. Using the above mentioned packaging solution, a CSAC with short-term frequency stability of about 7 × 10^-10τ-1/2 has been successfully achieved, which demonstrates that this physics package would become one promising solution for the CSAC.

Stable ^(85)Rb micro vapour cells:fabrication based on anodic bonding and application in chip-scale atomic clocks

We describe the microfabrication of ^85Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb. Under controlled conditions, the pure metallic Rb drops and buffer gases were obtained in the cells with a few mm^3 internal volumes during the cell sealing process. At an ambient temperature of 90 ℃ the optical absorption resonance of ^85Rb D1 transition with proper broadening and the corresponding coherent population trapping （CPT） resonance, with a signal contrast of 1.5% and linewidth of about 1.7 kHz, have been detected. The sealing quality and the stability of the cells have also been demonstrated experimentally by using the helium leaking detection and the after-9-month optoelectronics measurement which shows a similar CPT signal as its original status. In addition, the physics package of chip-scale atomic clock （CSAC） based on the cell was realized. The measured frequency stability of the physics package can reach to 2.1 × 10^-10 at one second when the cell was heated to 100 ℃ which proved that the cell has the quality to be used in portable and battery-operated devices.

植保无人机实时变量喷洒控制系统设计与试验

针对目前植保无人机在手动作业时,需要人为控制农药流量大小和植保机飞行速度,无法实现农药流量和飞行速度的实时匹配,造成农药喷洒不均匀的问题,开发了一种实时变量农药喷洒的控制系统。系统以STM32F103ZET6单片机为核心,使用GPS北斗定位模块进行速度和位置信息采集,基于PWM技术控制离心喷头的转速和水泵的药液流量,通过流量计反馈实时流量,形成闭环系统,并使用PID算法对整个系统进行精准控制。工作时,基于USART HMI串口屏设计的上位机远程实时地控制离心喷头转速和农药流量,同时在上位机的液晶屏幕上显示飞行参数等信息。试验结果表明:植保无人机实时变量喷洒控制系统可行,系统开机初始化时间为3.5s;在地面站离主设备1m~1km之间,系统响应时间为10~45ms之间,且农药流量控制系统的实际流量和理论流量之间的平均误差为2.2%。

增厚DBR型894 nm窄线宽VCSEL

垂直腔面发射激光器(VCSEL)是芯片级原子钟(CSAC)的主流光源,其光束质量会影响CSAC的各项性能。扩展VCSEL内部有效腔长能够以压缩冷腔线宽的方式压窄器件最终辐射激光的线宽,从而可以减小CSAC短时间内的计时频率噪声。根据所计算的VCSEL表面反射谱,将VCSEL中4层下分布式布拉格反射镜(DBR)的厚度由常规的四分之一波长增加至404 nm,压缩了VCSEL冷腔线宽,并生长了对应的外延结构,制备了通过增厚DBR扩展有效腔长的894 nm窄线宽VCSEL。测试结果表明,研制的VCSEL在90℃下波长为893.1 nm,功率为0.335 mW,线宽约为32 MHz,且具有稳定的偏振特性。

冷原子光栅磁光阱的研制及CPT信号的探询

相干布居囚禁原子钟在小型化方面具备不可替代的优势。由于热原子气室内部高压缓冲气体的限制,导致其频率稳定度仍有进一步提升的空间。利用激光冷却原子技术作为替代,可以有效提升其中长期性能。然而,目前的冷原子物理系统仍然相对复杂,不利于原子钟整体系统的集成化和小型化。我们研制了高衍射效率光栅芯片、平面磁阱芯片以及微小型真空腔室,共同构建基于平面核心器件的磁光阱,利用单光束捕获冷原子2×106个。此外,为了简化CPT冷原子钟的激光系统,通过单激光结合时分复用系统的方式,仅用单一Rb D2线激光实现了原子冷却与CPT探询。以上的工作为将来实现微小型化高性能冷原子CPT钟的最终锁定和性能评估奠定了重要理论和技术基础。

原子陀螺研究进展及展望

原子陀螺是基于量子物理原理和量子技术的新型高性能惯性传感器,在国防、军用以及民用等领域均具有广阔的应用前景,已成为国内外惯性技术领域的研究热点。目前原子陀螺主要分为核磁共振陀螺、无自旋交换弛豫陀螺和原子干涉陀螺,分别对它们的研究历程和现状进行了详细介绍,并对原子陀螺的未来发展趋势方向进行了展望,最后针对国内原子陀螺技术研究提出了一些思考。

基于MEMS技术的原子气室封装工艺

在基于MEMS技术原子气室的制备工艺中,难度较大的是碱金属的填充技术及阳极键合封装工艺,该工艺流程直接影响原子气室的质量。为进一步简化原子气室的制备工艺,设计了“双腔式”原子气室结构,采用先阳极键合,再化学反应的方法实现了原子气室批量化的封装。单个原子气室体积为6 mm×4 mm×2.5 mm,经氦气细检漏气率平均达到5×10^(-8)Pa·m^(3)·s^(-1),通过搭建实验平台,测得了不同温度下的原子气室D1线吸收谱线图,实验结果表明原子气室封装成功。

高精度时钟芯片在OBN中的应用

我国海洋油气资源丰富,海洋油气资源勘探是未来国家油气勘探开发的重要领域。OBN是当前海洋地震采集的主流仪器,OBN内部使用的时钟芯片的精度是评鉴地震采集资料的主要因素之一。本文重点介绍了恒温晶振及芯片级原子钟等高精度时钟芯片的原理,以及其在OBN中所关注的主要性能指标,通过几种时钟芯片在OBN中的实际应用及测试数据对比,说明高精度时钟芯片能够满足OBN在水下作业的性能要求,为OBN在海洋油气资源勘探领域的应用打下良好的基础。

芯片级原子钟研究进展

芯片级原子钟是一种小体积、低功耗的高精度时钟,适合作为便携式时频设备广泛应用于科学研究、生产生活、军事领域等方面。本文介绍了芯片级原子钟的国内外研究进展,阐述了芯片级原子钟的原理及研制的关键技术,介绍了芯片级原子钟的发展方向,并对我国芯片级原子钟的战略发展方向进行了展望。

芯片表面形貌检测方法及系统研制

传统检测方法由于测量范围小、测量时间长,不能满足在线、在机和大幅面的检测需求,本文提出了一种白光扫描干涉和原子力显微测量相结合的芯片表面形貌测量方法。在分析了白光扫描干涉测量技术和原子力显微测量技术特点的基础上,构建了两种方法互补的测量方案:首先采用白光扫描干涉测量技术对芯片进行大范围快速扫描,再通过原子力显微测量技术对关键区域进行精细扫描检测。基于此进行了测量系统的硬件设计与集成,测试结果表明,该系统能够在毫米级检测范围内实现纳米级表面形貌的精确测量。

基于改进多路径匹配追踪的芯片超声信号去噪方法

针对高频超声检测倒装焊芯片微缺陷的回波信号受噪声影响的问题,提出了一种基于改进多路径匹配追踪算法(MMP)的高频超声信号稀疏去噪方法。利用MMP算法获取全局最优的原子,针对MMP计算量过大的问题,在迭代过程中设置阈值和引入剪枝操作,筛选误差较大的路径,减少迭代路径,降低算法复杂度。为了避免字典维度上升导致的计算量过大,通过构建连续原子库对重构信号参数进行调整,最终实现芯片超声检测信号噪声的抑制。通过仿真和实验证明,提出的方法能够有效的去除倒装芯片高频超声检测信号中的噪音,与其他去噪算法相比,所提方法通过增加少量的计算,实现信号重构精度的提高,提升了B扫图的清晰度。