基于原子干涉仪的微观粒子弱等效原理检验

等效原理是广义相对论的两个基本假设之一,也是爱因斯坦对弱等效原理的推广.目前,大量实验证明弱等效原理在一定的实验精度内是成立的.将引力与标准模型统一起来的新理论都要求弱等效原理破缺,因此更高精度的弱等效原理检验具有重要的科学意义.本文介绍了原子干涉仪的原理,回顾了利用原子干涉仪开展微观粒子弱等效原理检验实验研究的历史和现状,介绍了双组分原子干涉仪检验弱等效原理实验涉及的振动噪声抑制、拉曼光移频与相位噪声抑制、四波双衍射拉曼跃迁原子干涉、信号探测与数据处理等关键问题及研究进展,分析了高精度微观粒子弱等效原理检验研究的发展趋势,介绍了长基线原子干涉仪、空间原子干涉仪、超冷原子源以及纠缠原子源制备等方面的研究动态,展望了微观粒子弱等效原理检验研究的发展前景.     

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.     

On the equivalence principle in quantum theory

The role of the equivalence principle in the context of non-relativistic quantum mechanics and matter wave interferometry, especially atom beam interferometry, will be discussed. A generalised form of the weak equivalence principle which is capable of covering quantum phenomena too, will be proposed. It is shown that this generalised equivalence principle is valid for matter wave interferometry and for the dynamics of expectation values. In addition, the use of this equivalence principle makes it possible to determine the structure of the interaction of quantum systems with gravitational and inertial fields. It is also shown that the path of the mean value of the position operator in the case of gravitational interaction does fulfill this generalised equivalence principle.     

A precision analysis and determination of the technical requirements of an atom interferometer for gravity measurement

The influence of the wave-front curvature of Raman pulses on the measurement precision of gravitational acceleration in atom interferometry is analysed by the method of a transmission matrix. It is shown that the measurement precision of gravitational acceleration is largely dependent on the spot size of the Raman pulse, the temporal interval between Raman pulses and the optical path difference of the two counter-propagating Raman pulses. Moreover, the influence of Doppler frequency shift on the precision is discussed. In order to get a certain measurement precision, the requirement for the accuracy of frequency scanning of the Raman pulse to compensate for the Doppler frequency shift is obtained.      

Repulsive gravitational effect of a quantum wave packet and experimental scheme with superfluid helium

We consider the gravitational effect of quantum wave packets when quantum mechanics, gravity, and thermodynamics are simultaneously considered. Under the assumption of a thermodynamic origin of gravity, we propose a general equation to describe the gravitational effect of quantum wave packets. In the classical limit, this equation agrees with Newton’s law of gravitation. For quantum wave packets, however, it predicts a repulsive gravitational effect. We propose an experimental scheme using superfluid helium to test this repulsive gravitational effect. Our studies show that, with present technology such as superconducting gravimetry and cold atom interferometry, tests of the repulsive gravitational effect for superfluid helium are within experimental reach.     

HYPER: A Satellite Mission in Fundamental Physics Based on High Precision Atom Interferometry

The article presents the HYPER project, a proposal for a satellite mission on precision matter-wave interferometry. For the mission several scientific objectives are under investigation, for which atom interferometers proved on ground to be a true complementary and competitive alternative for classical concepts: The application of atom interferometers as gyroscopes, the measurement of the gravitational acceleration (including tests of the universality of the free fall of atoms) and the precise determination of the fine-structure constant. The paper focuses on the use of cold-atom gyroscopes to map the Lense-Thirring effect close by the Earth and reports on results of recent feasibility studies of the European Space Agency. HYPER requires new concepts of compact, high-resolution matter-wave gyroscopes, which are better adapted to the use in satellite based experiments. The article will give a concise overview of the status and strategies in the field.     

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.     

Atom interferometry gravity-gradiometer for the determination of the Newtonian gravitational constant G

We developed a gravity-gradiometer based on atom interferometry for the determination of the Newtonian gravitational constant G. The apparatus, combining a Rb fountain, Raman interferometry and a juggling scheme for fast launch of two atomic clouds, was specifically designed to reduce possible systematic effects. We present instrument performances and preliminary results for the measurement of G with a relative uncertainty of 1%. A discussion of projected accuracy for G measurement using this new scheme shows that the results of the experiment will be significant to discriminate between previous inconsistent values.     

绝对重力仪的技术发展:光学干涉和原子干涉

绝对重力仪是直接开展绝对重力测量的精密计量仪器.绝对重力测量是指对地球表面重力加速度值的直接测量,其在地球科学和计量科学等领域都有十分重要的应用.历史上最早的绝对重力测量约在1590年.1590～1960年,主要利用摆仪的摆长和自由摆周期来开展绝对重力测量.自1960年起,随着激光技术的发明,高精度绝对重力测量有了新的...     

Tests of gravitational symmetries with radio pulsars

Symmetries play important roles in modern theories of physical laws. In this paper, we review several experimental tests of important symmetries associated with the gravitational interaction, including the universality of free fall for self-gravitating bodies, time-shift symmetry in the gravitational constant, local position invariance and local Lorentz invariance of gravity, and spacetime translational symmetries. Recent experimental explorations for post-Newtonian gravity are discussed, of which, those from pulsar astronomy are highlighted. All of these tests, of very different aspects of gravity theories, at very different length scales, favor to very high precision the predictions of the strong equivalence principle (SEP) and, in particular, general relativity which embodies SEP completely. As the founding principles of gravity, these symmetries are motivated to be promoted to even stricter tests in future.     

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.     

Optical visualization of internal gravity waves in stratified fluid

The refractive index changes associated with flows in salt water systems allow such flows to be visualized by means of optical methods, e.g. schlieren and interferometry. Experiments that have been conducted by our group with internal gravity waves in stratified brine are reviewed. The experiments encompass visualization and quantitative measurement of internal gravity waves generated by a body oscillating around a fixed position and a test body moving with constant speed vertically through the stratified brine. It is also shown that the velocity field of an internal gravity wave can be measured by means of particle image velocimetry. References to respective wave theories are made.     

Approximate Real–Time Visualization of a Quantum Transition by Means of Continuous Fuzzy Measurement

For the detection of gravitational waves the quantum mechanical properties of the detector have to be taken into account. Not all gravitational wave detectors allow a quantum nondemolition (QND) measurement. Continuous weak or fuzzy measurements are an alternative to study the evolution of a quantum mechanical system under the influence of an external field. In the present paper we investigate this alternative by applying it to a simplified system. We numerically simulate continuous fuzzy measurements of the oscillations of a two-level atom subjected to a resonant external light field. We thereby address the question whether it is possible to measure characteristic features of the evolution of a single quantum system in real time without relying on a QND scheme. We compare two schemes of continuous measurement: continuous measurement with constant fuzziness and with fuzziness changing in the course of the measurement. Because the sensitivity of the two-level atom to the influence of the measurement depends on the state of the atom, it is possible to optimize the continuous fuzzy measurement by varying its fuzziness.     

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.     

基于滑模鲁棒算法的超低频主动隔振系统

振动噪声的有效隔离是冷原子重力仪的关键技术之一.为了减小冷原子重力仪中拉曼反射镜的振动噪声,研制了一套紧凑型低频主动隔振系统.其原理是利用滑模鲁棒控制系统处理和反馈由地震仪采集到的振动信号,利用音圈电机控制和消除被动隔振平台的运动.在0.1—10 Hz频域范围内,滑模鲁棒控制系统的残余振动噪声功率谱密度比被动隔振平台最大降低了99.9%,比超前滞后补偿控制方法最大降低了83.3%.滑模鲁棒控制算法还具有整定参数少、抗干扰能力强等特点.     

数字散斑干涉三维变形测量技术研究进展

三维变形可以转换为应力/应变分布,是材料性能测试和结构可靠性分析的关键参数。在众多三维变形测量技术中,数字散斑干涉技术可以高精度地测量三维变形信息,在航空航天、汽车、先进制造、土木工程和生物医学等行业发挥着十分重要的作用。从散斑干涉基本原理出发,详细介绍了几类三维变形散斑干涉测量技术,并分析比较各类方法的优缺点;同时介绍了散斑干涉三维变形测量技术的国内外研究进展和最新应用;最后展望了散斑干涉三维变形测量技术在动态同步测量、测量系统简化以及应用范围扩宽等方面的发展趋势。     

万有引力常数G精确测量实验进展

万有引力常数G是人类历史上引入的第一个基本物理学常数,其在理论物理、天体物理和地球物理等许多领域中扮演着重要角色.两百多年来,人们共测量出了200多个G值,但G的测量精度仍然是所有物理学常数中最差的,这一现象反映了测G工作本身的复杂性和困难性.本文简要概述了G值测量的意义和测G的历史,并结合自2010年以来国际上新出现的三个高精度测G实验介绍这一领域的研究进展,以及华中科技大学引力实验中心测G工作的最新动态.     

Common-mode noise rejection using fringe-locking method in WEP test by simultaneous dual-species atom interferometers

We theoretically investigate the application of the fringe-locking method(FLM) in the dual-species quantum test of the weak equivalence principle(WEP).With the FLM,the measurement is performed invariably at the midfringe,and the extraction of the phase shift for atom interferometers is linearized.For the simultaneous interferometers,this linearization enables a good common-mode rejection of vibration noise,which is usually the main limit for high precision WEP tests of the dual-species kind.We note that this method also allows for an unbiased determination of the gravity accelerations difference,which meanwhile is ready to be implemented.     

Gravitational Shielding Effect in Gauge Theory of Gravity

In 1992, E.E. Podkletnov and R. Nieminen found that under certain conditions, ceramic superconductor with composite structure reveals weak shielding properties against gravitational force. In classical Newton's theory of gravity and even in Einstein's general theory of gravity, there are no grounds of gravitational shielding effects. But in quantum gauge theory of gravity, the gravitational shielding effects can be explained in a simple and natural way. In quantum gauge theory of gravity, gravitational gauge interactions of complex scalar field can be formulated based on gauge principle. After spontaneous symmetry breaking, if the vacuum of the complex scalar field is not stable and uniform, there will be a mass term of gravitational gauge field. When gravitational gauge field propagates in this unstable vacuum of the complex scalar field, it will decays exponentially, which is the nature of gravitational shielding effects. The mechanism of gravitational shielding effects is studied in this paper, and some main properties of gravitational shielding effects are discussed.     

Determination of the newtonian gravitational constant using atom interferometry

We present a new measurement of the Newtonian gravitational constant G based on cold-atom interferometry. Freely falling samples of laser-cooled rubidium atoms are used in a gravity gradiometer to probe the field generated by nearby source masses. In addition to its potential sensitivity, this method is intriguing as gravity is explored by a quantum system. We report a value of G = 6.667 x 10(-11) m(3) kg(-1) s(-2), estimating a statistical uncertainty of +/-0.011 x 10(-11) m(3) kg(-1) s(-2) and a systematic uncertainty of +/-0.003 x 10(-11) m(3) kg(-1) s(-2). The long-term stability of the instrument and the signal-to-noise ratio demonstrated here open interesting perspectives for pushing the measurement accuracy below the 100 ppm level.