基于阿基米德螺线的三导线环形磁导引

提出了一种三线阿基米德螺线结构产生环形磁势阱以囚禁中性原子的导引方案.该结构具有π/3旋转对称性,由三根导线组成.每根导线包含一对由圆弧连接的阿基米德螺线,且具有中心对称性.这种结构能够避免电流引线端导致的导引缺口问题.当加载直流电时,可以形成闭合的环形磁导引,但导引中心存在磁场零点.利用时间轨道平均势原理,在直流电的基础上再加载交流调制,对调制电流的参数进行分析和讨论后给出优化方案,使环形磁导引中心无磁场零点,同时平滑了环形磁导引中心磁场强度在角向上的起伏变化.该结构可以刻蚀在芯片表面,具有生产工艺简单、调制稳定等优点,有利于实现导引型原子芯片陀螺仪.     

单腔原子芯片系统中高效率的四极磁阱转移

利用两对部分重叠的磁光阱(MOT)和转移线圈产生的可移动四极磁阱(QMT)实现了87Rb冷原子从MOT中心向原子芯片的高效率输运。采取了线性增加转移线圈电流、同时保持MOT线圈电流不变的QMT移动方式,磁阱的移动速度构型为类Blackman型。利用该QMT输运方案,冷原子从MOT中心转移到原子芯片表面,转移过程中冷原子温度升高约30μK,原子转移效率高于90%。该系统可以为原子芯片干涉仪提供合适的冷原子源,也可以用来研究原子与芯片表面的相互作用。     

冷原子的双阱微磁表面囚禁

提出了两种新颖的采用载流导线的双阱微磁表面囚禁方案(即双U形与双Z形导线囚禁)。通过改变囚禁方案中直导线中的电流方向，即可将双U形导线囚禁改变为双Z形导线囚禁；如果逐渐减小直导线中的电流大小，即可将一个双阱微磁囚禁连续地合并为一个单阱微磁囚禁，反之亦然。详细计算和分析了上述两种载流导线囚禁方案的磁场及其梯度的空间分布。研究发现在导线中通以较小的电流，即可在导线表面附近产生很大的磁场梯度及其曲率。例如当电流为O．2A时，其磁场梯度和曲率可分别达到0．2T／cm和10T／cm2以上。由于双U形导线囚禁中存在磁场零点，而双Z形导线囚禁中仅存在磁场最小值，所以双U形导线囚禁仅适用于制备双样品磁光囚禁(MOT)或研究中性原子的冷碰撞，而双Z形导线囚禁除了可用于研究原子的冷碰撞之外，还可以用于制备双样品玻色-爱因斯坦凝聚(BEC)或实验研究双阱玻色-爱因斯坦凝聚的性质等。     

非线性磁光效应用于测量磁光阱四极磁场的方案

为了研究磁光阱冷原子团所在区域的磁场大小,从而得出磁场零点附近磁场的微弱变化及其分布。提出利用右旋圆偏振作为探测光场穿过冷原子,根据左右旋圆偏振光场引起的跃迁几率的不同,导致穿过冷原子团零点前后探测场跃迁几率的变化,用来计算零点附近由冷原子团引起的非线性磁光效应,通过这一效应推导出旋转角随磁场大小的变化,从而获得了磁光阱四极磁场零点附近数量级达到10^-13T的磁场值。利用这一效应,同时在理论上获得了不同于以往理论及实验的双峰色散曲线。     

利用原子芯片上Z形磁阱囚禁中性87Rb原子

利用解析和数值方法计算了Z形磁阱的囚禁势,发现当囚禁中心和芯片表面距离较远时(该距离和Z形线中部导线的一半长度相差不超过一个量级),势阱的深度不能近似表示成偏置磁场By对应的能量,而要减去囚禁中心的势能高度;而增加By进行磁阱压缩到一定值时,势阱深度反而会下降.此外介绍了原子芯片的制作方法,以及利用原子芯片上Z形磁阱囚禁中性87Rb原子的实验装置和实验过程.最终有2×106个87Rb原子被转移到Z形磁阱中.     

采用U-型载流导体的原子磁导引及其原子光学器件

本文提出了一种采用U型载流导体实现冷原子磁导引的新方案，计算了U型载流导体在空间产生的磁场分布。研究发现该方案不仅可用于弱场搜寻态原子的单通道磁导引，而且也可用于冷原子的双通道磁导引，甚至用于实现可控制的相干物质波(BEC)的单模双波导，从而为构建各种原子光学器件(如原子漏斗，原子分束器及原子干涉仪等)提供一种新的实验方案。此外，由U型载流导体构成的分束器不需要外加任何偏磁场，这给实验带了很大的方便。最后，采用Monte-Carlo模拟方法，就冷原子在U型载流导体分束器中的分束过程进行了动力学模拟，得到了分束器两个输出端的原子分布及其分束比与工作参数的依赖关系，为进一步的实验研究提供了理论依据。     

中性原子的表面双磁光阱及其应用

提出了一种新的采用载流导线的表面双磁光阱(MOT)方案(即双U型导线磁光阱方案)。通过改变中间U型导线中的电流大小,即可将一个双磁阱连续地合并为一个单磁阱,反之亦然。详细计算和分析了上述双U型载流导线磁光阱方案的磁场及其梯度的空间分布,研究发现当导线中的电流为600 A,z方向均匀偏置磁感应强度为-4.0×10-3 T时,双U型导线方案产生的两个磁阱中心的磁场梯度约为1.5×10-3~2.5×10-3 T/cm,结合通常制备磁光阱时所用的三维粘胶(Molasses)光束即可在基底表面附近形成一双磁光阱。理论分析表明在弱光近似下,每个磁光阱中所能俘获的85Rb原子数约为106 量级,相应的磁光阱温度约为270μK。由于双磁光阱可以独立制备,所以双U型导线方案特别适用于制备双样品磁光阱,并用于研究双原子样品的冷碰撞性质。     

用于全光铯原子磁力仪的激光器稳频技术研究

全光铯原子磁力仪是采用光学的方法实现微弱磁场检测,激光频率稳定性直接影响磁力仪的灵敏度。分析了二向色性原子蒸气激光频率锁定(Dichroic atomic vapor laser lock DAVLL)技术用于稳定激光器频率的原理,及其在全光原子磁力仪中的应用优势,发现通常的二能级原子模型不适用于分析铯原子D2线的稳频。实验测量了不同磁场下铯原子D2线基态Fg=4和Fg=3跃迁的DAVLL光谱,发现16mT是实现DAVLL稳频的最佳磁场;在此磁场附近,基态Fg=4跃迁鉴频曲线零点相对于Fg=4→Fe=5跃迁会产生6MHz/mT的线性频移,基态Fg=3跃迁鉴频曲线零点相对于Fg=3→Fe=4线会产生-9MHz/mT的线性频移。     

抽运-检测型原子磁力仪对电流源噪声的测量

用于在宽量程范围内标定原子磁力仪的灵敏度的复现磁场通常由精密电流源和标准线圈产生,电流源噪声将直接影响原子磁力仪在宽量程范围内标定的灵敏度.本文基于抽运-检测型原子磁力仪首先提出抑制复现磁场漂移的磁补偿方法,其次开展宽量程范围内电流源的噪声和原子磁力仪的灵敏度之间依赖关系的研究.研究结果表明,抽运-检测型原子磁力仪的灵敏度主要由电流源噪声决定,因此可用特定磁场下的灵敏度估算电流源在对应输出电流条件下的电流噪声.本文研究对弱磁传感器灵敏度指标的标定、高精度电流源的研制、磁感应强度计量和电流计量的协同发展都具有参考价值.     

线极化Bell-Bloom测磁系统中抽运光对磁场灵敏度的影响

利用适用于线极化Bell-Bloom测磁系统的布洛赫方程和含有自旋弛豫的速率方程,以铯原子为研究对象,分析了抽运光对磁场灵敏度的影响,并在实验上分别采用与铯原子D1线和D2线共振的线偏光作为抽运光和探测光,用充有缓冲气体的气室进行了实验.实验结果与理论分析一致,均表明只有在一定的光强范围内,增大抽运光光强可以提高磁场灵敏度.且利用这一方法分析了原子的自旋弛豫对磁场灵敏度的影响.这项研究对于深入认识线极化的Bell-Bloom测磁系统,以及如何通过优化系统实现磁场灵敏度的提高具有重要的意义.     

Smooth Archimedean-spiral ring waveguide for cold atomic gyroscope

We propose a robust scheme that creates a toroidal magnetic potential on a single-layer atom chip. The wire layout consists of two interleaved Archimedean spirals, which avoids the trapping perturbation caused by the input and output ports. By using a rotation bias field, the minimum of the time-averaged orbiting potential is lifted from zero, and then a relatively smooth and harmonic ring trap is formed. The location of the waveguide is immune to the magnetic variations, as it is only determined by the wire layout. The ring waveguide offers an ideal solution to developing a compact and portable atomic gyroscope.     

Guiding Neutral Atoms with Two Current-Carrying Wires and a Vertical Bias Field on the Atom Chip

We demonstrate the guiding of neutral atoms with two parallel microfabricated current-carrying wires on the atom chip and a vertical magnetic bias field. The atoms are guided along a magnetic field minimum parallel to the current-carrying wires and confined in the other two directions. We describe in detail how the precooled atoms are efficiently loaded into the two-wire guide. We present a detailed experimental study of the motional properties of the atoms in the guide and the relationship between the location of the guide and the vertical bias field. This two-wire guide with vertical bias field can be used to realize large area atom interferometer.     

Superconducting atom chips: advantages and challenges

Superconductors are considered in view of applications to atom chip devices. The main features of magnetic traps based on superconducting wires in the Meissner and mixed states are discussed. The former state may mainly be interesting for improved atom optics, while in the latter, cold atoms may provide a probe of superconductor phenomena. The properties of a magnetic side guide based on a single superconducting strip wire placed in an external magnetic field are calculated analytically and numerically. In the mixed state of type II superconductors, inhomogeneous trapped magnetic flux, relaxation processes and noise caused by vortex motion are posing specific challenges for atom trapping.     

Guiding neutral atoms on a chip

We demonstrate the guiding of neutral atoms by the magnetic fields due to microfabricated current-carrying wires on a chip. Atoms are guided along a magnetic field minimum parallel to and above the current-carrying wires. Two guide configurations are demonstrated: one using two wires with an external magnetic field, and a second using four wires without an external field. These guide geometries can be extended to integrated atom optics circuits, including beam splitters.     

Roughness suppression via rapid current modulation on an Atom chip

We present a method to suppress the roughness of the potential of a wire-based, magnetic atom guide: modulating the wire current at a few tens of kHz, the potential roughness, which is proportional to the wire current, averages to zero. Using ultracold 87Rb clouds, we show experimentally that modulation reduces the roughness by at least a factor five without measurable heating or atom loss. This roughness suppression results in a dramatic reduction of the damping of center-of-mass oscillations.     

The effect of domain wall motion on the nondiagonal impedance component in amorphous wires with circular magnetic anisotropy

The effect of the domain wall motion on the nondiagonal impedance component in amorphous ferromagnetic wires with circular anisotropy was theoretically studied. The frequency spectrum of the electromotive force (emf) induced in the pick-up coil wound around the wire is analyzed. For sufficiently small amplitudes of the ac current passing in the wire, the emf frequency equals doubled frequency of the current. For the ac current amplitudes exceeding certain threshold value, all even harmonics appear in the frequency spectrum of the signal. The emf strongly depends on the longitudinal component of the applied magnetic field at any value of the ac current amplitude. These results can be important for developing frequency transducers controlled by magnetic field.     

Generation of spin current by Coulomb drag

Coulomb drag between two quantum wires is exponentially sensitive to the mismatch of their electronic densities. The application of a magnetic field can compensate this mismatch for electrons of opposite spin directions in different wires. The resulting enhanced momentum transfer leads to the conversion of the charge current in the active wire to the spin current in the passive wire.     

Atom chips in the real world: the effects of wire corrugation

We present a detailed model describing the effects of wire corrugation on the trapping potential experienced by a cloud of atoms above a current carrying micro wire. We calculate the distortion of the current distribution due to corrugation and then derive the corresponding roughness in the magnetic field above the wire. Scaling laws are derived for the roughness as a function of height above a ribbon shaped wire. We also present experimental data on micro wire traps using cold atoms which complement some previously published measurements [CITE] and which demonstrate that wire corrugation can satisfactorily explain our observations of atom cloud fragmentation above electroplated gold wires. Finally, we present measurements of the corrugation of new wires fabricated by electron beam lithography and evaporation of gold. These wires appear to be substantially smoother than electroplated wires.