克尔非线性黑体中光超流态的研究

研究了克尔非线性黑体中一种新的光超流态.研究表明:非线性黑体中具有相反波矢和旋量的裸光子结合成对,未成对的裸光子则转换成一种新的准粒子——非极化激元;光子对系统是一个超流态,而非极化激元系统是一个正常流态.正常流态的光谱能量密度和辐射压强都比普通黑体大并且随温度单调增加.在理论上证明了克尔非线性黑体中光超流态的存在并给出了测量这种光超流态的方法.

Physics package based on intracavity laser cooling ^(87)Rb atoms for space cold atom microwave clock

This article proposes a new physics package to enhance the frequency stability of the space cold atom clock with the advantages of a microgravity environment. Clock working processes, including atom cooling, atomic state preparation,microwave interrogation, and transition probability detection, are integrated into the cylindrical microwave cavity to achieve a high-performance and compact physics package for the space cold atom clock. We present the detailed design and ground-test results of the cold atom clock physics package in this article, which demonstrates a frequency stability of 1.2×10^(-12) τ^(-1/2) with a Ramsey linewidth of 12.5 Hz, and a better performance is predicted with a 1 Hz or a narrower Ramsey linewidth in microgravity environment. The miniaturized cold atom clock based on intracavity cooling has great potential for achieving space high-precision time-frequency reference in the future.

Planar ion chip design for scalable quantum information processing

We investigate a planar ion chip design with a two-dimensional array of linear ion traps for scalable quantum information processing. Qubits are formed from the internal electronic states of trapped ^40Ca^＋ ions. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate separately, a combination of appropriate rf and DC potentials is applied to them for stable ion confinement. Every two adjacent electrodes can generate a linear ion trap in and between the electrodes above the chip at a distance dependent on the geometrical scale and other considerations. The potential distributions are calculated by using a static electric field qualitatively. This architecture provides a conceptually simple avenue to achieving the microfabrication and large-scale quantum computation based on the arrays of trapped ions.

Surface Planar Ion Chip for Linear Radio-Frequency Paul Traps

We propose a surface planar ion chip which forms a linear radio frequency Paul ion trap. The electrodes reside in the two planes of a chip, and the trap axis is located above the chip surface. Its electric field and potential distribution are similar to the standard linear radio frequency Paul ion trap. This ion trap geometry may be greatly meaningful for quantum information processing.

Development of the integrated integrating sphere cold atom clock

We develop an integrated integrating sphere cold atom clock(ISCAC), which mainly consists of physical package,laser system, microwave source, and electronics.This compact system is more stable and reliable than the previous version.The experimental results show that the short term frequency stability of 5.4×10^-13τ-1/2 and 2.9× 10^-15 at 1-day integrating time are achieved.

Development of an Integrating Sphere Cold Atom Clock

The Ramsey fringes with a linewidth of 45 Hz and a signal-to-noise ratio of 120 are demonstrated for a integrating sphere atom clock.The cycle time of the atom clock is reduced to 80 ms with the help of a pulsed cooling method.This result indicates that the short-term stability of the clock is in the order of 10^(-12).

Three-Dimensional Array for 40Ca＋ Ion Trapping

We present a three-dimensional scalable linear ion trap scheme for ion trapping and discuss its applications for the optical frequency standard and scalable quantum information processing with its parallel strings of trapped 40Ca＋ ions. The geometry here contains nine equal-distance parallel rods driven by rf, which form trapping potentials for radial confinement and two end ring electrodes biased at a few volts for axial confinement. Its feasibility is calculated by using the finite element analysis method.

An effective pumping method for increasing atomic utilization in a compact cold atom clock

We propose a simple pumping method to increase the effective population of cold atoms in the clock state and investigate the factors which affect the pumping efficiency in cold atom systems.We report the theory and demonstrate the corresponding experiment in an ^(87)Rb integrating sphere cold atom clock.The experimental results show that the population of cold atoms in the Zeeman sublevel|F=2,mF=0>is approximately 1.62 times that of the result using optical pumping alone.This method can also be applied to increase the effective population in any one of the target Zeeman sublevels in other cold atom systems.

Observation of Faraday Rotation in Cold Atoms in an Integrating Sphere

The Faraday rotation of weak linearly polarized probe light is observed as it passes through a sample of cold ^87Rb atoms prepared by diffused light in an integrating sphere. The rotation angle of the probe light-polarization as functions of laser intensity, detuning and biased magnetic field is measured. A Ramsey fringe with a linewidth of 35 Hz and contrast up to 92% is demonstrated. This method has potential applications in improving the performance of atomic clocks with cold atoms.

Integrated, reliable laser system for an ^(87)Rb cold atom fountain clock

We designed, assembled, and tested a reliable laser system for ^(87)Rb cold atom fountain clocks. The laser system is divided into four modules according to function, which are convenient for installing, adjusting, maintaining, and replacing of the modules. In each functional module, all optical components are fixed on a baseplate with glue and screws, ensuring the system's structural stability. Mechanical stability was verified in a 6.11g RMS randomvibration test, where the change in output power before and after vibration was less than 5%. Thermal stability was realized by optimizing of the structure and appropriate selection of component materials of the modules through thermal simulation. In the laser splitting and output module, the change in laser power was less than 20% for each fiber in thermal cycles from 5℃ to 43℃. Finally,the functionality of the laser system was verified for a rubidium fountain clock.

Dick Effect in the Integrating Sphere Cold Atom Clock

The Dick effect is an important factor limiting the frequency stability of sequentially-operating atomic frequency standards. Here we study the impact of the Dick effect in the integrating sphere cold atom clock （ISCAC）. To reduce the impact of the Dick effect, a 5 MHz local oscillator with ultra-low phase noise is selected and a new microwave synthesizer is built in-house. Consequently, the phase noise of microwave signal is optimized. The contribution of the Dick effect is reduced to 2.5× 10^-13τ-1/2 （3- is the integrating time）. The frequency stability of 4.6 × 10-13τ-1/2 is achieved. The development of this optimization can promote the space applications of the compact ISCA C.

An Optimum Method for a Grooved 2D Planar Ion Trap Design

We investigate an effective grooved 2D ion chip design and optimize the ratio between the size of the rf electrodes and the groove.We calculate the optimal size of the groove using the analytical model,which was introduced by House,and the optimum result is obtained.We also obtain the simulated scattering points with the finite element analysis method.The analytical curve and simulated scattering points are coincident with each other.It is shown that this analytical model also fits for the grooved planar ion chip.Thus the optimum grooved 2D planar ion chip design could be obtained.It is effective for scalable quantum information processing.

A grooved planar ion trap design for scalable quantum information processing

We describe a new electrode design for a grooved surface-electrode ion trap,which is fabricated in printed-circuitboard technology with segmented electrodes.This design allows a laser beam to get through the central groove to avoid optical access blocking and laser scattering from the ion trap surface.The confining potentials are modeled both analytically and numerically.We optimize the radio frequency（rf） electrodes and dc electrodes to achieve the maximum trap depth for a given ion height above the trap electrodes.We also compare our design with the reality ion chip MI I for practical considerations.Comparison results show that our design is superior to MI I.This ion trap design may form the basis for large scale quantum computers or parallel quadrupole mass spectrometers.

积分球冷原子钟相位调制Ramsey条纹研究

在进行Ramsey作用时,以±π/2的相位差来调制同一频率点处两个周期微波脉冲,可以获得中心频率幅值为零的Ramsey条纹。这种方法可以直接通过中心频率处原子对探测光的吸收值变化来产生反馈本地振荡器的误差信号。理论上,相比于同相位Ramsey条纹,这种方法可以使得条纹信号幅值增加一倍。实验上,在积分球冷原子钟系统上,获得的相位调制Ramsey线型与理论计算相同,而且Ramsey条纹振荡幅值达到同相位下的1.6倍。

积分球与微波腔一体化装置的研制

首先对一体化的积分球微波腔进行了论证,然后进行了设计、仿真和加工实测。采用单端环耦合的方式进行微波激励,分别对从圆柱腔的端面及侧面耦合的方式进行了仿真,结果发现在圆柱腔侧面耦合能得到较好的场型分布。实现了通过微调耦合环的方式进行模式选择的新方法,这种方法简便易行,且能有效减小微波腔的体积。测试结果表明设计的微波腔体积小、结构稳定,能同时满足积分球冷却和微波腔的功能要求即实现了积分球与微波腔一体化的要求,更重要的是一体化结构不需要使用漫反射涂料,不会影响腔的模式及场型分布,有利于提高钟信号的信噪比和对比度。

积分球冷原子钟的探测光频率和强度噪声

对积分球冷原子钟(ISCAC)探测光的频率和强度噪声进行了理论分析和实验研究。通过功率稳定和杂散光去除,探测光相对强度噪声的功率谱密度在高频区域(0.1~10kHz)最大被压缩了15dB,同时探测光频率噪声对ISCAC频率稳定度的影响被降低至9τ^(-1/2)×10^(-15),其中τ为积分时间。理论分析结果表明,目前探测光频率噪声对ISCAC频率稳定度的影响为2.5τ^(-1/2)×10^(-13)。提出了一种减小探测光频率噪声影响的实验方案,即在钟周期一定时适当增大探测时间。采用这种方法,可以将探测光频率噪声对ISCAC频率稳定度的影响减小至9.4τ^(-1/2)×10^(-14)。

积分球冷原子钟冷原子数稳定的新方法

提出了一种积分球冷原子钟冷原子数稳定的新方法。该方法通过周期性地监测冷原子的吸收信号,利用反馈控制冷却激光内声光调制器的衍射效率并改变冷却光功率,实现冷原子数的稳定。推导了冷原子数稳定系统的环路方程,分析了稳定环路对冷原子数涨落的抑制作用。稳定后冷原子数的归一化涨落为1±0.001(3h),其功率谱密度在0.001~0.2Hz频率范围内的最大抑制量约为30dB。该涨落被抑制的原因主要是稳定环路除了直接补偿冷却光激光器输出的光功率变化外,还纠正了外界环境引起的冷原子数漂移。冷原子数稳定之后,由冷原子数涨落引起的原子钟频率稳定度可降低至7×10^(-14)τ^(-1/2)(τ为积分时间)。

微波腔镀银实现漫反射冷却的实验研究

观测到了使用镀银微波腔产生漫反射光场冷却原子的信号,完成了微波腔与积分球一体化的最后一步。这种冷却方式结构更加简单,且没有涂料,不会对微波场场型造成影响,有利于钟信号的信噪比及对比度提高。同时测试了微波腔冷却在不同冷却光注入方案、漫反射系数及腔表面开孔尺寸下的冷却性能。结果表明端面注入冷却光是目前获得更多冷原子数目的方法,提高腔表面的漫反射系数,可以显著提高冷原子数目。为了充分利用积分球内的冷原子,采用了10mm的通光孔径,测试了不同通光孔径对冷原子信号的影响,证实了目前较大的通光孔径不会影响到冷原子数。

可扩展的用于量子信息处理的刻槽平面离子芯片设计

研究设计了一个有效的可扩展的二维刻槽离子芯片。为了减少激光在离子芯片表面的散射,使被囚禁离子更加稳定,并使激光容易控制和探测成行的被囚禁离子,在每两个平行的射频电极中间刻槽使冷却光和探测光路径可穿过芯片。把控制离子运动的直流电极跟射频电极分开,减轻了不同电压对被囚禁离子的干扰,改进了对离子的控制。用有限元分析的方法对芯片表面上方的电势分布做了计算模拟。模拟结果表明,在这种新型的刻槽可扩展芯片上可以生成一个可扩展的离子阱阵列。这种结构提供了一个新颖的刻槽二维平面离子芯片,被囚禁其上的线形离子阵列可用来进行大型的量子信息处理。

拉曼喷泉原子钟

利用拉曼光场代替喷泉原子钟的微波腔实现拉曼喷泉原子钟。将分离拉曼光场技术与冷原子喷泉技术相结合,避免了在真空腔内放置微波腔,简化了真空系统,同时还保持了很高的准确度。采用半经典理论研究了冷原子喷泉与拉曼光场的相互作用过程,得到了冉赛(Ramsey)条纹。比较了拉曼喷泉原子钟与热铯束拉曼原子钟,前者有更小的体积和功耗,其精度可能达到或超过商用小铯钟。还比较了拉曼喷泉原子钟与微波喷泉原子钟的差别,分析了光子反冲的影响,提出利用同向传播和相向传播的两台拉曼原子钟测量精细结构常数。