不同序列拉曼光脉冲对原子重力仪灵敏度的影响

研究了不同序列拉曼光脉冲对原子重力仪灵敏度的影响.结果表明,通过调节脉冲间隔可以改善原子干涉重力仪的灵敏度.在标准配置下,只考虑重力及一阶重力梯度时,三脉冲序列（π/2-π-π/2）的原子干涉重力仪具有较大的灵敏度,四脉冲序列（π/2-π-π-π/2）的原子干涉重力仪对重力不敏感,可用来测量重力梯度,五脉冲作用会降低原子干涉重力仪的灵敏度. 关键词： 原子重力仪 拉曼激光脉冲序列 灵敏度     

Six-axis inertial sensor using cold-atom interferometry

We have developed an atom interferometer providing a full inertial base. This device uses two counterpropagating cold-atom clouds that are launched in strongly curved parabolic trajectories. Three single Raman beam pairs, pulsed in time, are successively applied in three orthogonal directions leading to the measurement of the three axis of rotation and acceleration. In this purpose, we introduce a new atom gyroscope using a butterfly geometry. We discuss the present sensitivity and the possible improvements.     

Atom interferometry with trapped fermi gases

We realize an interferometer with an atomic Fermi gas trapped in an optical lattice under the influence of gravity. The single-particle interference between the eigenstates of the lattice results in macroscopic Bloch oscillations of the sample. The absence of interactions between fermions allows a time-resolved study of many periods of the oscillations, leading to a sensitive determination of the acceleration of gravity. The experiment proves the superiority of noninteracting fermions with respect to bosons for precision interferometry and offers a way for the measurement of forces with microscopic spatial resolution.     

Atom interferometry with a weakly interacting Bose-Einstein condensate

We demonstrate the operation of an atom interferometer based on a weakly interacting Bose-Einstein condensate. We strongly reduce the interaction induced decoherence that usually limits interferometers based on trapped condensates by tuning the s-wave scattering length almost to zero via a magnetic Feshbach resonance. We employ a 39K condensate trapped in an optical lattice, where Bloch oscillations are forced by gravity. The fine-tuning of the scattering length down to 0.1 a_(0) and the micrometric sizes of the atomic sample make our system a very promising candidate for measuring forces with high spatial resolution. Our technique can be in principle extended to other measurement schemes opening new possibilities in the field of trapped atom interferometry.     

光和原子关联与量子计量

物理量的测量与单位标准的统一推动了计量学的发展.量子力学的建立,激光技术的发明以及原子与分子物理学的发展,在原理与技术上进一步刷新了计量学的研究内涵,特别是激光干涉与原子频标技术的发展,引起了计量学革命性的飞跃.基于激光干涉的引力波测量、激光陀螺仪,基于原子干涉的原子钟、原子陀螺仪等精密测量技术相继诞生,一个以量子物理为基础,探索与开拓物理量精密测量方法与技术的新的科学分支——量子计量学(Quantum Metrology)已然兴起.干涉是计量学中最常用的相位测量方法.量子干涉技术,其相位测量精度能够突破标准量子极限的限制,是量子计量学与量子测量技术的核心研究内容.本文重点介绍近几年我们在量子干涉方面所取得的新开拓与新发展,主要内容包括基于原子系综中四波混频过程的SU(1,1)型光量子关联干涉仪和基于原子系综中拉曼散射过程的光-原子混合干涉仪.     

Development of an atom gravimeter and status of the 10-meter atom interferometer for precision gravity measurement

Experimental realizations of cold ⁸⁵Rb atom interferometers in Wuhan are reviewed in this paper. The application of atom interferometers in local gravity measurement are reported. The resolutions of gravity measurement are 2.0 × 10⁻⁷g for 1 s and 4.5 × 10⁻⁹g for 1,888 s. The absolute g value was derived with a difference of 1.6 × 10⁻⁷g compared to the gravity reference value. The tidal phenomenon was observed by continuously monitoring the local gravity over 123 h. A 10-meter atom interferometer designed for precision gravity measurement and the equivalence principle test is under construction, the latest status is reported for the first time.     

利用原子干涉仪的相位调制进行绝对转动测量

提出一种基于原子干涉仪的相位调制进行绝对转动测量的方法.以π/2-π-π/2构型的空间型原子干涉仪为例,通过对拉曼激光进行相位调制,然后在动量谱空间测量转动对原子速度谱的调制周期,获得原子干涉仪相对惯性空间的绝对转动.文章对于采用该法进行角速度测量的测量范围以及对相位调制频率的要求进行了分析,对于散粒噪声限下的转动测量灵敏度及其影响因素进行了仿真. 关键词： 原子干涉仪 原子陀螺 相位调制 绝对转动测量     

高灵敏度的量子迈克耳孙干涉仪

迈克耳孙干涉仪不仅可以用来研究物理学的基本问题,而且能够用于精密测量,比如引力波信号的测量.因此,构建高灵敏度的迈克耳孙干涉仪是实现微弱信号测量的关键.目前,人们利用压缩态可以降低迈克耳孙干涉仪的噪声;通过光学四波混频过程能够放大马赫·曾德尔干涉仪中的相位信号,从而提高干涉仪的信噪比和灵敏度.本文研究了一种用于高灵敏度相位测量的量子迈克耳孙干涉仪.在迈克耳孙干涉仪中,利用非简并光学参量放大器取代干涉仪中的线性光学分束器;并且将压缩态注入干涉仪的真空通道,可以得到高信噪比和高灵敏度的干涉仪.由于存在不可避免的光学损耗,分析了迈克耳孙干涉仪内部和外部的损耗对相位测量灵敏度的影响.通过理论计算研究了干涉仪的相位测量灵敏度随系统参数的变化关系,得到了高灵敏度的相位测量量子迈克耳孙干涉仪的实现条件,为用于精密测量的干涉仪的设计提供了直接参考.     

Light-pulse atom interferometry in microgravity

We describe the operation of a light pulse interferometer using cold ⁸⁷Rb atoms in reduced gravity. Using a series of two Raman transitions induced by light pulses, we have obtained Ramsey fringes in the low gravity environment achieved during parabolic flights. With our compact apparatus, we have operated in a regime which is not accessible on ground. In the much lower gravity environment and lower vibration level of a satellite, our cold atom interferometer could measure accelerations with a sensitivity orders of magnitude better than the best ground based accelerometers and close to proven spaced-based ones.     

新型高精度绝对重力仪

精密测量地球表面的重力加速度(g, 常用值9.81 m/s²) 是探测地球重力场的重要途径, 已广泛应用于计量、测绘、地质、地震与资源勘探等领域. 随着我国"2000国家重力基本网"和"中国地壳运动观测网络"的建成, 对高精度绝对重力测量的需求日益增加. 为深入研究现有绝对重力测量技术可能存在的系统误差, 并满足国内多个领域对高精度绝对重力仪的迫切需求, 自主研制T-1型可搬运式高精度绝对重力仪样机, 采用经典的真空自由落体方案, 通过激光干涉测量和数据拟合方法获得重力加速度值. T-1型绝对重力仪主要包括以下几部分: 高真空度自由落体装置、小型化激光干涉测量装置、超低频垂直隔振系统、高速信号采集系统、仪器控制与数据处理系统. 绝对重力测量的长度基准为稳频He-Ne激光器, 时间基准为铷原子钟, 这两项现有基准的测量不确定度都优于1× 10^-9. 测试结果表明, T-1型绝对重力仪在12 h内重力测值的标准差可优于1 μupGal (1 μupGal = 10^-8 m/s²), 测量结果的复现性优于3 μupGal, 可实现微伽量级不确定度的精密重力测量, 有望在我国多个关键领域发挥重要应用.     

Influence of lasers propagation delay on the sensitivity of atom interferometers

In atom interferometers based on two photon transitions, the delay induced by the difference of the laser beams paths makes the interferometer sensitive to the fluctuations of the frequency of the lasers. We first study, in the general case, how the laser frequency noise affects the performance of the interferometer measurement. Our calculations are compared with the measurements performed on our cold atom gravimeter based on stimulated Raman transitions. We finally extend this study to the case of cold atom gradiometers.     

Atom-interferometry tests of the isotropy of post-Newtonian gravity

We present a test of the local Lorentz invariance of post-Newtonian gravity by monitoring Earth's gravity with a Mach-Zehnder atom interferometer that features a resolution of up to 8 x 10{-9}g/sqrt[Hz], the highest reported thus far. Expressed within the standard model extension (SME) or Nordtvedt's anisotropic universe model, the analysis limits four coefficients describing anisotropic gravity at the ppb level and three others, for the first time, at the 10 ppm level. Using the SME we explicitly demonstrate how the experiment actually compares the isotropy of gravity and electromagnetism.     

The magnesium ramsey interferometer: Applications and prospects

In this paper it will be shown that an atom interferometer, based on the coherent splitting of the atomic wavefunction by four travelling waves (Ramsey interferometer), may be explained by a purely mechanical interpretation. As our first application of this Ramsey interferometer we have measured the phase shifts respectively optical length changes in a magnesium atomic beam caused by the acceleration of the partial atomic wave in one arm of the interferometer. This acceleration was achieved by the dipole force exerted by an off-resonant crossing laser beam which interacted with the ground state part of the wavefunction only. Further applications of this interferometer and improvements due to laser cooling will be discussed.     

Development of an atom-interferometer gravity gradiometer for gravity measurement from space

Recent progress in cold atom interferometry has lead to a new method of sensitive inertial sensing. Significant performance enhancement of cold atom interferometer-based sensors is anticipated when operated in the microgravity environment in space. Based on cold atom interferometer techniques, we are developing a quantum gravity gradiometer for satellite-based global gravity field mapping. As a first step, we have built a laboratory-based gradiometer employing component technologies suitable for a future flight instrument. This paper describes the implementation of the laboratory instrument and its initial results. PACS 03.75.Dg; 39.20.+q; 32.80.Pj; 04.80.-y     

Geometric phase of an accelerated two-level atom in the presence of a perfectly reflecting plane boundary

We study the geometric phase of a uniformly accelerated two-level atom coupled with vacuum fluctuations of electromagnetic fields in the presence of a perfectly reflecting plane. We find that the geometric phase difference between the accelerated and inertial atoms which can be observed by atom interferometry crucially depends on the polarizability of the atom and the distance to the boundary and it can be dramatically manipulated with anisotropically polarizable atoms. In particular, extremely close to the boundary, the phase difference can be increased by two times as compared to the case without any boundary. So, the detectability of the effects associated with acceleration using an atom interferometer can be significantly increased by the presence of a boundary using atoms with anisotropic polarizability.     

用于冷原子干涉仪激光时序控制的DDS跳频系统设计与实现

为了满足冷原子干涉实验对时序控制的需求,设计并实现了一个基于LABVIEW软件的激光时序控制DDS系统,其工作过程为通过设计的LABVIEW上位机软件输入需要产生的频率和频率间隔时间,ARM芯片根据LABVIEW软件发送来的控制信息实现对射频信号芯片的控制,CPLD芯片用来控制射频信号之间的时间间隔,最后DDS芯片产生与控制信息相对应的射频信号。与目前同类装置相比,系统实现了跳频时间和频率更加精确和工作稳定性更好。经过系统的调试分析以及性能测试,DDS跳频系统能够满足原子干涉仪激光时序控制需求。通过测试DDS装置,DDS装置能够输出准确输出射频频率值,并且射频频率时间间隔能精确到微秒。DDS装置可以有效控制冷原子干涉仪的激光时序,在探询时间为120毫秒且重复率为2.2赫兹的情况下,冷原子重力仪的重力测量灵敏度达到 。     

基于阿基米德定律测量重力加速度

基于阿基米德定律设计一种测量重力加速度的实验装置,对重力加速度进行测量.通过本实验得到的重力加速与当地重力加速度标准值的相对误差为0.14%,这为实验测量室重力加速度提供一种新方法。     

Limitations of atom interferometry for gravitational wave observations in space

A paper published recently (Hogan et al. in Gen. Relativ. Gravit. 43:1953–2009, 2011) suggests the use of atom interferometry between satellites in Earth orbit to observe gravitational waves. The proposed altitude and satellite separation are about 1,000 and 30 km respectively. The difference in acceleration between clouds of ultracold atoms in atom interferometers near the two satellites would be detected by using laser beams between the interferometers. Because of the measurement path being very short compared with the million km or longer measurement path for a proposed laser interferometer gravitational wave antenna in space, the sensitivity to differential fluctuations in the laser phase as seen by the atoms in the two atom interferometers is very high. Problems introduced by this high sensitivity to spurious laser beam phase changes will be described in the first part of this paper. Then other limitations on the performance and on the suggested types of sources that could be observed will be discussed.     

模拟函数法测定重力加速度

模拟函数法测重力加速度是针对传统的重力加速度测定中没有考虑空气阻力影响而采用的一种新型方法。本文采用此法测定了当地的重力加速度，得到了较满意的效果。