When the cold atom clock operates in microgravity around the near-earth orbit, its performance will be affected by the fluctuation of magnetic field. A strategy is proposed to suppress the fluctuation of magnetic fiel...When the cold atom clock operates in microgravity around the near-earth orbit, its performance will be affected by the fluctuation of magnetic field. A strategy is proposed to suppress the fluctuation of magnetic field by additional coils, whose current is changed accordingly to compensate the magnetic fluctuation by the linear and incremental compensation. The flight model of the cold atom clock is tested in a simulated orbital magnetic environment and the magnetic field fluctuation in the Ramsey cavity is reduced from 17 nT to 2 nT, which implied the uncertainty due to the second order Zeeman shift is reduced to be less than 2×10^（-16）. In addition, utilizing the compensation, the magnetic field in the trapping zone can be suppressed from 7.5 μT to less than 0.3 μT to meet the magnetic field requirement of polarization gradients cooling of atoms.展开更多
20th century physics experimentally established beyond doubt the fact that moving clocks read differently from “static” clocks. This fact is typically interpreted as support for special relativity. On the other hand...20th century physics experimentally established beyond doubt the fact that moving clocks read differently from “static” clocks. This fact is typically interpreted as support for special relativity. On the other hand, the same century produced proof that clocks at various locations in the gravitational field also read differently, and this fact is explained by general relativity, which is, in general, not Lorentz transformable. This paper establishes a common framework for the physics of clocks in these different situations.展开更多
High precision and stable clock is extremely important in communication and navigation.The miniaturization of the clocks is considered to be the trend to satisfy the demand for5G and the next generation communications...High precision and stable clock is extremely important in communication and navigation.The miniaturization of the clocks is considered to be the trend to satisfy the demand for5G and the next generation communications.Based on the concept of meter bar and the principle of the constancy of light velocity,we designed a micro clock,Space Time Clock(STC),with the size smaller than 1 mm×1 mm and the power dissipation less than 2 m W.Designed in integrated circuit of 0.18μm technology,the instability of STC is assessed to be 2.23×10^(-12)and the trend of the instability is reversely proportional toτ.With the potential ability to reach the level of 10instability on chip in the future,the period of the STC’s signal is locked on the delay time defined by the meter bar which keeps the time reference constant.Because of its superior performance,the STC is more suitable for mobile communication,PNT(Positioning,Navigation and Timing),embedded processor and deep space application,and becomes the main payload of the ASRTU satellite scheduled to launch next year and investigate in space environment.展开更多
As an extension of the＂teleparallel＂equivalent of general relativity,f（T）gravity is proposed to explain some puzzling cosmological behaviors,such as accelerating expansion of the Universe.Given the fact that modif...As an extension of the＂teleparallel＂equivalent of general relativity,f（T）gravity is proposed to explain some puzzling cosmological behaviors,such as accelerating expansion of the Universe.Given the fact that modified gravity also has impacts on the Solar System,we might test it during future interplanetary missions with ultrastable clocks.In this work,we investigate the effects of f（T）gravity on the dynamics of the clock and its time transfer link.Under these influences,theΛ-term and theα-term of f（T）gravity play important roles.Here,Λis the cosmological constant andαrepresents a model parameter in f（T）gravity that determines the divergence from teleparallel gravity at the first order approximation.We find that the signal of f（T）gravity in the time transfer is much more difficult to detect with the current state of development for clocks than those effects on dynamics of an interplanetary spacecraft with a bounded orbit with parameters 0.5 au≤a≤5.5 au and 0≤e≤0.1.展开更多
Einstein relativity theory shows its high capability of promoting itself to solve the long stand physical problems. The so-called generalized special relativity (GSR) was derived later, using the beautiful Einstein re...Einstein relativity theory shows its high capability of promoting itself to solve the long stand physical problems. The so-called generalized special relativity (GSR) was derived later, using the beautiful Einstein relation between field and space-time curvature. In this work we re-derive (GSR) expression of time by incorporating the field effect in it, and by using mirror clock and Lorentz transformations. This expression reduces to that of (GSR) the previous conventional one, besides reducing to special relativistic expression. It also shows that the speed of light is constant inside the field and is equal to C. This means that the observed decrease of light in matter and field is attributed to the strong interaction of photons with particles and mediates which causes successive absorption and reemission processes that lead to time delay. This absorption process makes some particles appear to move faster than light within the field or medium. This new expression, unlike that of GSR, can describe time and coordinate relativistic expressions for strong as well as weak fields at constant acceleration.展开更多
We report on studies of an optical lattice for a strontium clock performed at the National Time Service Center. Follow-ing tw o-stage laser cooling and trapping,88 Sr cold atoms w ith population of 105 and a longitudi...We report on studies of an optical lattice for a strontium clock performed at the National Time Service Center. Follow-ing tw o-stage laser cooling and trapping,88 Sr cold atoms w ith population of 105 and a longitudinal temperature of 8. 4 μK are loaded into a one-dimensional optical lattice. Spectroscopic analysis of the1S0-3P0 transition gives a linew idth of 180 Hz measured using magnetic field-induction,w hich mixes the3P1 state w ith the3P0 state. Rabi oscillations are observed. Because of the inhomogeneous excitation among the atoms,the Rabi π-pulse excitation at 5 ms show s a near 65% excitation of atoms. The transverse velocity distribution of the atomic beam and the absolute frequencies of the four inter-combination transitions of the isotopes w as measured precisely using velocity-selective fluorescence spectroscopy. By optical injection of tw o cascade external-cavity diode lasers,a single comb line at 689 nm from an optical femtosecond laser comb is filtered and amplified w ith a 37-d B side-mode suppression and a linew idth of less than 240 Hz. We describe recent w ork on a space optical clock concerning the physical vacuum system,thermal analysis,and a permanent-magnet Zeeman slow er for a space strontium optical clock. The first six mode frequencies are obtained and the corresponding oscillation modes are described in detail. We also simulate and analyze thermal profiles for both the physical and optical units installed in the cooling system. When the injected cooling w ater has a temperature of 21℃ or28℃,the units meet operational requirements for temperatures in a space environment. Using a series of permanent magnets,a Zeeman slow er is built that can w ithstand space launching and operating conditions for the space optical clock.展开更多
Metrological analysis shows that any clock in inertial motion in infinite space shall not have time dilation, due to relativity of such motion in such space. On the other hand, atomic clock in inertial motion in finit...Metrological analysis shows that any clock in inertial motion in infinite space shall not have time dilation, due to relativity of such motion in such space. On the other hand, atomic clock in inertial motion in finite space shall exhibit time dilation, due to alteration of momentum of clock-defining particle caused by nonzero curvature of trajectory of such motion in such space. Therefore, time dilation experiment of atomic clock in inertial motion in physical space provides a direct and decisive way of determining geometry of physical space in real-time. Phenomenon of time dilation of atomic clock in inertial motion in physical space has long been observed and confirmed experimentally. Therefore, extent of physical space has to be finite, consistent with result of high precision experiment of free particle in high-speed motion conducted a decade ago.Keywords Geometry of Physical Space, Time Dilation, Atomic Clock, Special Relativity Theory.展开更多
近年来,随着多系统全球导航卫星系统(global navigation satellite system,GNSS)的迅速发展以及实时高精度应用需求的日益增长,国际GNSS服务分析中心(International GNSS Service,IGS)提供的状态空间表述(state space representation,S...近年来,随着多系统全球导航卫星系统(global navigation satellite system,GNSS)的迅速发展以及实时高精度应用需求的日益增长,国际GNSS服务分析中心(International GNSS Service,IGS)提供的状态空间表述(state space representation,SSR)产品越来越丰富。评估不同分析中心的GNSS实时产品及其定位性能对用户具有重要参考价值。对中国科学院(Chinese Academy of Sciences,CAS)、法国太空研究中心(Centre National d’Etudes Spatiales,CNE)、德国宇航中心(Deutsches Zentrum für Luft-und Raumfahrt,DLR)、西班牙航天与防务公司(GMV Aerospace and Defense,GMV)、德国地学研究中心(Deutsches GeoForschungsZentrum,GFZ)、武汉大学(Wuhan University,WHU)6个分析中心的GPS/北斗卫星导航系统(BeiDou satellite navigation system,BDS)SSR产品的可用性、精度和实时精密单点定位性能进行了评估。实验结果表明:CAS播发的GPS卫星可用性最高,提供了所有32颗GPS卫星的SSR改正数;CAS、GFZ、WHU 3家分析中心的BDS卫星可用性相对较高,提供了15(BDS-2)+27(BDS-3)卫星的SSR改正数。在6个分析中心中,WHU的GPS卫星的三维轨道精度和钟差精度均为最佳;不同分析中心GPS卫星的信号空间测距误差(signal-in-space ranging errors,SISRE)普遍优于5 cm,不同分析中心GPS卫星的SISRE值的大小顺序为:WHU<GMV<CNE<DLR<GFZ<CAS;BDS卫星轨道钟差精度相对较差,表现最优的WHU分析中心的BDS-2和BDS-3的中地球轨道卫星精密产品的SISRE值分别为8.83、5.91 cm。在单GPS动态PPP模式下,DLR的收敛速度最慢,GFZ收敛速度最快;加入BDS卫星以后,定位精度无显著差异,但能够有效提升收敛速度。展开更多
实时轨道、钟差产品的精度和完好性是实现全球卫星导航系统精准可信定位服务的重要前提。以2022年中国科学院(Chinese Academy of Sciences,CAS)实时轨道、钟差产品为例,从产品精度及精密单点定位精度两个方面评估实时轨道、钟差产品性...实时轨道、钟差产品的精度和完好性是实现全球卫星导航系统精准可信定位服务的重要前提。以2022年中国科学院(Chinese Academy of Sciences,CAS)实时轨道、钟差产品为例,从产品精度及精密单点定位精度两个方面评估实时轨道、钟差产品性能,并根据全球均匀分布的100个虚拟测站计算得到的瞬时空间信号用户测距误差(instantaneous signal-in-space user range error,IURE),分析实时轨道、钟差产品的空间信号用户测距误差分布特性,计算CAS实时轨道、钟差产品的完好性支持信息。试验结果表明,以德国地学研究中心提供的事后精密产品为参考,GPS和Galileo的轨道精度优于5 cm,钟差标准差(standard deviation,STD)优于0.08 ns,BDS和GLONASS的轨道精度优于15 cm,STD优于0.3 ns;选取全球分布测站以静态仿动态方式进行精密单点定位测试,四系统组合定位的3D方向精度均方根(root mean square,RMS)优于4 cm,收敛时间优于11 min。GPS和Galileo的IURE RMS优于4 cm,同时IURE分布峰度基本在10以内,偏度绝对值基本在0.5以内,可接受为高斯分布;GLONASS的IURE RMS在10 cm以内,但是各卫星IURE的偏度和峰度之间差异较大,尖峰厚尾情况较为严重;BDS的IURE RMS优于11 cm,但是不同类型卫星的IURE分布不同,且BDS-3上海微小卫星工程中心的卫星具有较为明显的双峰特性。对于星座故障和卫星故障先验概率,GPS星座故障先验概率最小为5.2×10^(-5),除BDS-2外,其他系统星座故障先验概率小于1.0×10^(-3);GLONASS卫星故障先验概率达到2.7×10^(-3),Galileo卫星故障先验概率最小为8.7×10^(-4)。对于空间信号用户测距误差的包络标准差和标准差,GPS和Galileo卫星的两种标准差差异均在4 cm以内;GLONASS卫星的两种标准差差异基本大于5 cm;相较于标准差,BDS-2和BDS-3的包络标准差差异较大。展开更多
基金Project supported by the Ministry of Science and Technology of China(Grant No.2013YQ09094304)the Youth Innovation Promotion Association,Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant Nos.11034008 and 11274324)
文摘When the cold atom clock operates in microgravity around the near-earth orbit, its performance will be affected by the fluctuation of magnetic field. A strategy is proposed to suppress the fluctuation of magnetic field by additional coils, whose current is changed accordingly to compensate the magnetic fluctuation by the linear and incremental compensation. The flight model of the cold atom clock is tested in a simulated orbital magnetic environment and the magnetic field fluctuation in the Ramsey cavity is reduced from 17 nT to 2 nT, which implied the uncertainty due to the second order Zeeman shift is reduced to be less than 2×10^（-16）. In addition, utilizing the compensation, the magnetic field in the trapping zone can be suppressed from 7.5 μT to less than 0.3 μT to meet the magnetic field requirement of polarization gradients cooling of atoms.
文摘20th century physics experimentally established beyond doubt the fact that moving clocks read differently from “static” clocks. This fact is typically interpreted as support for special relativity. On the other hand, the same century produced proof that clocks at various locations in the gravitational field also read differently, and this fact is explained by general relativity, which is, in general, not Lorentz transformable. This paper establishes a common framework for the physics of clocks in these different situations.
基金National Natural Science Foundation of China(No.11973021)Harbin Institute of Technology,Research Centre of Satellite Technology and Department of Microelectronics Science and Technologysupported by the ASRTU satellite project。
文摘High precision and stable clock is extremely important in communication and navigation.The miniaturization of the clocks is considered to be the trend to satisfy the demand for5G and the next generation communications.Based on the concept of meter bar and the principle of the constancy of light velocity,we designed a micro clock,Space Time Clock(STC),with the size smaller than 1 mm×1 mm and the power dissipation less than 2 m W.Designed in integrated circuit of 0.18μm technology,the instability of STC is assessed to be 2.23×10^(-12)and the trend of the instability is reversely proportional toτ.With the potential ability to reach the level of 10instability on chip in the future,the period of the STC’s signal is locked on the delay time defined by the meter bar which keeps the time reference constant.Because of its superior performance,the STC is more suitable for mobile communication,PNT(Positioning,Navigation and Timing),embedded processor and deep space application,and becomes the main payload of the ASRTU satellite scheduled to launch next year and investigate in space environment.
基金Supported by the National Natural Science Foundation of China (Grant No. 11103010)funded by the Natural Science Foundation of China (Grant No. 11103085)+3 种基金the Fundamental Research Program of Jiangsu Province of China (Grant No. BK20131461Grant No. BK2011553)the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20110091120003)the Fundamental Research Funds for the Central Universities (No. 1107020116)
文摘As an extension of the＂teleparallel＂equivalent of general relativity,f（T）gravity is proposed to explain some puzzling cosmological behaviors,such as accelerating expansion of the Universe.Given the fact that modified gravity also has impacts on the Solar System,we might test it during future interplanetary missions with ultrastable clocks.In this work,we investigate the effects of f（T）gravity on the dynamics of the clock and its time transfer link.Under these influences,theΛ-term and theα-term of f（T）gravity play important roles.Here,Λis the cosmological constant andαrepresents a model parameter in f（T）gravity that determines the divergence from teleparallel gravity at the first order approximation.We find that the signal of f（T）gravity in the time transfer is much more difficult to detect with the current state of development for clocks than those effects on dynamics of an interplanetary spacecraft with a bounded orbit with parameters 0.5 au≤a≤5.5 au and 0≤e≤0.1.
文摘Einstein relativity theory shows its high capability of promoting itself to solve the long stand physical problems. The so-called generalized special relativity (GSR) was derived later, using the beautiful Einstein relation between field and space-time curvature. In this work we re-derive (GSR) expression of time by incorporating the field effect in it, and by using mirror clock and Lorentz transformations. This expression reduces to that of (GSR) the previous conventional one, besides reducing to special relativistic expression. It also shows that the speed of light is constant inside the field and is equal to C. This means that the observed decrease of light in matter and field is attributed to the strong interaction of photons with particles and mediates which causes successive absorption and reemission processes that lead to time delay. This absorption process makes some particles appear to move faster than light within the field or medium. This new expression, unlike that of GSR, can describe time and coordinate relativistic expressions for strong as well as weak fields at constant acceleration.
文摘We report on studies of an optical lattice for a strontium clock performed at the National Time Service Center. Follow-ing tw o-stage laser cooling and trapping,88 Sr cold atoms w ith population of 105 and a longitudinal temperature of 8. 4 μK are loaded into a one-dimensional optical lattice. Spectroscopic analysis of the1S0-3P0 transition gives a linew idth of 180 Hz measured using magnetic field-induction,w hich mixes the3P1 state w ith the3P0 state. Rabi oscillations are observed. Because of the inhomogeneous excitation among the atoms,the Rabi π-pulse excitation at 5 ms show s a near 65% excitation of atoms. The transverse velocity distribution of the atomic beam and the absolute frequencies of the four inter-combination transitions of the isotopes w as measured precisely using velocity-selective fluorescence spectroscopy. By optical injection of tw o cascade external-cavity diode lasers,a single comb line at 689 nm from an optical femtosecond laser comb is filtered and amplified w ith a 37-d B side-mode suppression and a linew idth of less than 240 Hz. We describe recent w ork on a space optical clock concerning the physical vacuum system,thermal analysis,and a permanent-magnet Zeeman slow er for a space strontium optical clock. The first six mode frequencies are obtained and the corresponding oscillation modes are described in detail. We also simulate and analyze thermal profiles for both the physical and optical units installed in the cooling system. When the injected cooling w ater has a temperature of 21℃ or28℃,the units meet operational requirements for temperatures in a space environment. Using a series of permanent magnets,a Zeeman slow er is built that can w ithstand space launching and operating conditions for the space optical clock.
文摘Metrological analysis shows that any clock in inertial motion in infinite space shall not have time dilation, due to relativity of such motion in such space. On the other hand, atomic clock in inertial motion in finite space shall exhibit time dilation, due to alteration of momentum of clock-defining particle caused by nonzero curvature of trajectory of such motion in such space. Therefore, time dilation experiment of atomic clock in inertial motion in physical space provides a direct and decisive way of determining geometry of physical space in real-time. Phenomenon of time dilation of atomic clock in inertial motion in physical space has long been observed and confirmed experimentally. Therefore, extent of physical space has to be finite, consistent with result of high precision experiment of free particle in high-speed motion conducted a decade ago.Keywords Geometry of Physical Space, Time Dilation, Atomic Clock, Special Relativity Theory.
文摘近年来,随着多系统全球导航卫星系统(global navigation satellite system,GNSS)的迅速发展以及实时高精度应用需求的日益增长,国际GNSS服务分析中心(International GNSS Service,IGS)提供的状态空间表述(state space representation,SSR)产品越来越丰富。评估不同分析中心的GNSS实时产品及其定位性能对用户具有重要参考价值。对中国科学院(Chinese Academy of Sciences,CAS)、法国太空研究中心(Centre National d’Etudes Spatiales,CNE)、德国宇航中心(Deutsches Zentrum für Luft-und Raumfahrt,DLR)、西班牙航天与防务公司(GMV Aerospace and Defense,GMV)、德国地学研究中心(Deutsches GeoForschungsZentrum,GFZ)、武汉大学(Wuhan University,WHU)6个分析中心的GPS/北斗卫星导航系统(BeiDou satellite navigation system,BDS)SSR产品的可用性、精度和实时精密单点定位性能进行了评估。实验结果表明:CAS播发的GPS卫星可用性最高,提供了所有32颗GPS卫星的SSR改正数;CAS、GFZ、WHU 3家分析中心的BDS卫星可用性相对较高,提供了15(BDS-2)+27(BDS-3)卫星的SSR改正数。在6个分析中心中,WHU的GPS卫星的三维轨道精度和钟差精度均为最佳;不同分析中心GPS卫星的信号空间测距误差(signal-in-space ranging errors,SISRE)普遍优于5 cm,不同分析中心GPS卫星的SISRE值的大小顺序为:WHU<GMV<CNE<DLR<GFZ<CAS;BDS卫星轨道钟差精度相对较差,表现最优的WHU分析中心的BDS-2和BDS-3的中地球轨道卫星精密产品的SISRE值分别为8.83、5.91 cm。在单GPS动态PPP模式下,DLR的收敛速度最慢,GFZ收敛速度最快;加入BDS卫星以后,定位精度无显著差异,但能够有效提升收敛速度。
文摘实时轨道、钟差产品的精度和完好性是实现全球卫星导航系统精准可信定位服务的重要前提。以2022年中国科学院(Chinese Academy of Sciences,CAS)实时轨道、钟差产品为例,从产品精度及精密单点定位精度两个方面评估实时轨道、钟差产品性能,并根据全球均匀分布的100个虚拟测站计算得到的瞬时空间信号用户测距误差(instantaneous signal-in-space user range error,IURE),分析实时轨道、钟差产品的空间信号用户测距误差分布特性,计算CAS实时轨道、钟差产品的完好性支持信息。试验结果表明,以德国地学研究中心提供的事后精密产品为参考,GPS和Galileo的轨道精度优于5 cm,钟差标准差(standard deviation,STD)优于0.08 ns,BDS和GLONASS的轨道精度优于15 cm,STD优于0.3 ns;选取全球分布测站以静态仿动态方式进行精密单点定位测试,四系统组合定位的3D方向精度均方根(root mean square,RMS)优于4 cm,收敛时间优于11 min。GPS和Galileo的IURE RMS优于4 cm,同时IURE分布峰度基本在10以内,偏度绝对值基本在0.5以内,可接受为高斯分布;GLONASS的IURE RMS在10 cm以内,但是各卫星IURE的偏度和峰度之间差异较大,尖峰厚尾情况较为严重;BDS的IURE RMS优于11 cm,但是不同类型卫星的IURE分布不同,且BDS-3上海微小卫星工程中心的卫星具有较为明显的双峰特性。对于星座故障和卫星故障先验概率,GPS星座故障先验概率最小为5.2×10^(-5),除BDS-2外,其他系统星座故障先验概率小于1.0×10^(-3);GLONASS卫星故障先验概率达到2.7×10^(-3),Galileo卫星故障先验概率最小为8.7×10^(-4)。对于空间信号用户测距误差的包络标准差和标准差,GPS和Galileo卫星的两种标准差差异均在4 cm以内;GLONASS卫星的两种标准差差异基本大于5 cm;相较于标准差,BDS-2和BDS-3的包络标准差差异较大。
