A frequency servo system-on-chip(FS-SoC)featuring output power stabilization technology is introduced in this study for high-precision and miniaturized cesium(Cs)atomic clocks.The proposed power stabilization loop(PSL...A frequency servo system-on-chip(FS-SoC)featuring output power stabilization technology is introduced in this study for high-precision and miniaturized cesium(Cs)atomic clocks.The proposed power stabilization loop(PSL)technique,incorporating an off-chip power detector(PD),ensures that the output power of the FS-SoC remains stable,mitigating the impact of power fluctuations on the atomic clock's stability.Additionally,a one-pulse-per-second(1PPS)is employed to syn-chronize the clock with GPS.Fabricated using 65 nm CMOS technology,the measured phase noise of the FS-SoC stands at-69.5 dBc/Hz@100 Hz offset and-83.9 dBc/Hz@1 kHz offset,accompanied by a power dissipation of 19.7 mW.The Cs atomic clock employing the proposed FS-SoC and PSL obtains an Allan deviation of 1.7×10^(-11) with 1-s averaging time.展开更多
We report an experimental demonstration of geopotential difference measurement using a pair of transportable ^(40)Ca^(+) optical clocks(TOC-729-1 and TOC-729-3)in the laboratory,each of them has an uncertainty of 1.3&...We report an experimental demonstration of geopotential difference measurement using a pair of transportable ^(40)Ca^(+) optical clocks(TOC-729-1 and TOC-729-3)in the laboratory,each of them has an uncertainty of 1.3×10^(−17) and an instability of 4.8×10^(−15)/√τ.Referenced to a stationary clock of TOC-729-1,the geopotential difference measurements are realized by moving TOC-729-3 to three different locations and the relevant altitude differences are measured with uncertainties at the level of 20 cm.After correcting the systematic shifts(including gravitational red shift),the two-clock frequency difference is measured to be–0.7(2.2)×10^(−17),considering both the statistic(1.0×10^(−17))and the systematic(1.9×10^(−17))uncertainties.The frequency difference between these two clocks is within their respective uncertainties,verifying the reliability of transportable ^(40)Ca^(+) optical clocks at the low level of 10^(−17).展开更多
The caesium atomic fountain clock is a primary frequency standard.During its operation,a Majorana transition frequency shift will occur once a magnetic field at some special locations along the atomic trajectory is si...The caesium atomic fountain clock is a primary frequency standard.During its operation,a Majorana transition frequency shift will occur once a magnetic field at some special locations along the atomic trajectory is singular.In this study,by developing a physical model,we analyzed the magnetic field requirements for atomic adiabatic transition and calculated the influence of the Majorana atomic transition on the atomic state via a quantum method.Based on the simulation results for the magnetic field in the fountain clock,we applied the Monte Carlo method to simulate the relationship between the Majorana transition frequency shift and the magnetic field at the entrance of the magnetic shielding,as well as the initial atomic population.Measurement of the Majorana transition frequency shift was realized by state-selecting asymmetrically populated atoms.The relationship between the Majorana transition frequency shift and the axial magnetic field at the entrance of the magnetic shielding was obtained.The measured results were essentially consistent with the calculated results.Thus,the magnetic field at the entrance of the magnetic shielding was configured,and the Majorana transition frequency shift of the fountain clock was calculated to be 4.57×10^(-18).展开更多
The study of magnetic field effects on the clock transition of Mg and Cd optical lattice clocks is scarce.In this work,the hyperfine-induced Landég-factors and quadratic Zeeman shift coefficients of the nsnp ^(3)...The study of magnetic field effects on the clock transition of Mg and Cd optical lattice clocks is scarce.In this work,the hyperfine-induced Landég-factors and quadratic Zeeman shift coefficients of the nsnp ^(3)P_(0)^(o) clock states for ^(111,113)Cd and ^(25)Mg were calculated by using the multi-configuration Dirac–Hartree–Fock theory.To obtain accurate values of these parameters,the impact of electron correlations and furthermore the Breit interaction and quantum electrodynamical effects on the Zeeman and hyperfine interaction matrix elements,and energy separations were investigated in detail.We also estimated the contributions from perturbing states to the Landég-factors and quadratic Zeeman shift coefficients concerned so as to truncate the summation over the perturbing states without loss of accuracy.Our calculations provide important data for estimating the first-and second-order Zeeman shifts of the clock transition for the Cd and Mg optical lattice clocks.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
The optical atomic clocks have the potential to transform global timekeeping,relying on the state-of-the-art accuracy and stability,and greatly improve the measurement precision for a wide range of scientific and tech...The optical atomic clocks have the potential to transform global timekeeping,relying on the state-of-the-art accuracy and stability,and greatly improve the measurement precision for a wide range of scientific and technological applications.Herein we report on the development of the optical clock based on 171Yb atoms confined in an optical lattice.A minimum width of 1.92-Hz Rabi spectra has been obtained with a new 578-nm clock interrogation laser.The in-loop fractional instability of the 171Yb clock reaches 9.1×10-18 after an averaging over a time of 2.0×104 s.By synchronous comparison between two clocks,we demonstrate that our 171Yb optical lattice clock achieves a fractional instability of 4.60×10-16/√τ.展开更多
The Al^+ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic...The Al^+ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of AI+ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al^+ traps are utilized. The first trap is used to trap a large number of Al^+ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al^+ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167nm laser. The expected clock laser stability can reach 9.0 × 10^-17/√τ. For the second trap, in addition to 167nm laser Doppler cooling, a second stage pulsed 234nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about 1 × 10^-18. The proposed Al^+ ion optical clock has the potential to become the most accurate and stable optical clock.展开更多
Foreign-made clocks and watches began to be exported to China in the 17th century. During the Qing Dynasty (1644-1911), the imperial court imported tens of thousands of clocks and watches. At the Palace Museum in Beij...Foreign-made clocks and watches began to be exported to China in the 17th century. During the Qing Dynasty (1644-1911), the imperial court imported tens of thousands of clocks and watches. At the Palace Museum in Beijing, about 200 timepieces collected by the imperial court are still on display in the clock and watch exhibition hall. They were made in Britain, France, Switzerland and Japan. Many foreign presidents and展开更多
Research on chip-scale atomic clocks (CSACs) based on coherent population trapping (CPT) is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed t...Research on chip-scale atomic clocks (CSACs) based on coherent population trapping (CPT) is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the re- liability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance's collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research.展开更多
Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in...Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in 1016, and the best optical clock has reached a type B uncertainty below 10-18. Besides applications in the metrology, navigation, etc.,ultra-stable and ultra-accurate atomic clocks have also become powerful tools in the basic scientific investigations. In this paper, we focus on the recent developments in the high-performance cold atomic clocks which can be used as frequency standards to calibrate atomic time scales. The basic principles, performances, and limitations of fountain clocks and optical clocks based on signal trapped ion or neutral atoms are summarized. Their applications in metrology and other areas are briefly introduced.展开更多
We describe the microfabrication of ^85Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb. Under controlled conditions...We describe the microfabrication of ^85Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb. Under controlled conditions, the pure metallic Rb drops and buffer gases were obtained in the cells with a few mm^3 internal volumes during the cell sealing process. At an ambient temperature of 90 ℃ the optical absorption resonance of ^85Rb D1 transition with proper broadening and the corresponding coherent population trapping (CPT) resonance, with a signal contrast of 1.5% and linewidth of about 1.7 kHz, have been detected. The sealing quality and the stability of the cells have also been demonstrated experimentally by using the helium leaking detection and the after-9-month optoelectronics measurement which shows a similar CPT signal as its original status. In addition, the physics package of chip-scale atomic clock (CSAC) based on the cell was realized. The measured frequency stability of the physics package can reach to 2.1 × 10^-10 at one second when the cell was heated to 100 ℃ which proved that the cell has the quality to be used in portable and battery-operated devices.展开更多
General relativity theory(GRT)concludes that a precise clock ticks at different running rates if it is under the influence of different geopotentials.Therefore,by comparing the running rates of clocks at arbitrary two...General relativity theory(GRT)concludes that a precise clock ticks at different running rates if it is under the influence of different geopotentials.Therefore,by comparing the running rates of clocks at arbitrary two stations,the geopotential difference between them can be determined.In this study,with the help of two hydrogen atomic clocks(noted as H-masers),using the two-way satellite time and frequency transfer(TWSTFT)technique,we carried out experiments of the geopotential difference determination at the China Aerospace Science&Industry Corporation(CASIC),Beijing.Here the ensemble empirical mode decomposition(EEMD)method is adopted to remove periodic signals included in the original observations.Finally,the clock-comparison-determined geopotential difference in the experiments is determined.Results show that the difference between the geopotential difference determined by GRT and that determined by measuring tape is about 1316.1±931.0 m2s-2,which is equivalent to 134.3±95.0 m in height,and in consistence with the stability of the H-masers applied in the experiments(at the level of10-15/day).With the rapid improvement of atomic clocks’accuracy,the geopotential determination by accurate clocks is prospective,and it is promising to realize the unification of the world vertical height system(WVHS).展开更多
We develop a permanent-magnet Zeeman slower with adjustable magnets along the longitudinal and radial directions.Produced by four arrays of cylindrical magnets, the longitudinal magnetic field in the slower is tunable...We develop a permanent-magnet Zeeman slower with adjustable magnets along the longitudinal and radial directions.Produced by four arrays of cylindrical magnets, the longitudinal magnetic field in the slower is tunable if relevant parameters vary, for example, laser detuning or intensity. The proposed Zeeman slower can be reconfigured for Sr atoms. Additionally,we demonstrate that the residual magnetic field produced by the permanent magnets in the magneto-optical trap region can be as small as 0.5 Gs.展开更多
A method that obtains the Ramsey-coherent population trapping (CPT) spectrum with the Faraday effect is investi- gated. An experiment is implemented to detect the light polarization components generated from the Far...A method that obtains the Ramsey-coherent population trapping (CPT) spectrum with the Faraday effect is investi- gated. An experiment is implemented to detect the light polarization components generated from the Faraday effect. The experimental results agree with the theoretical calculations based on the Liouville equation. By comparing with the method without using the Faraday effect, the potential of this method for a CPT-based atomic clock is assessed. The results indicate that this method should improve the short-term frequency stability by several times.展开更多
Based on the multiconfiguration Dirac-Hartree-Fock(MCDHF)method,similar models are employed to simultaneously calculate the first-order and second-order Zeeman coefficients as well as the hyperfine interaction constan...Based on the multiconfiguration Dirac-Hartree-Fock(MCDHF)method,similar models are employed to simultaneously calculate the first-order and second-order Zeeman coefficients as well as the hyperfine interaction constants of the related energy levels of ^(27)Al^(+)and its logical ions ^(9)Be^(+)and^(25)Mg^(+)in the^(27)Al^(+)optical clock.With less than 0.34%deviations from experimental values in Zeeman coefficients of^(27)Al^(+),these calculated parameters will be of great help for better evaluation of the systematic uncertainty.We also calculate the isotope shift parameters of the related energy levels,which could extend our knowledge and understanding of nuclear properties of these ions.展开更多
We demonstrate an optical frequency comb(OFC)based on a turnkey mode-locked laser with a figure-9-shape structure and polarization-maintaining fibers,for the comparison of frequency among optical clocks with wavelengt...We demonstrate an optical frequency comb(OFC)based on a turnkey mode-locked laser with a figure-9-shape structure and polarization-maintaining fibers,for the comparison of frequency among optical clocks with wavelengths of 698 nm,729 nm,1068 nm,and 1156 nm.We adopt a multi-branch approach in order to produce high power OFC signals at these specific wavelengths,enabling the signal-to-noise ratio of the beatnotes between the OFC and the clock lasers to exceed30 d B at a resolution bandwidth of 300 k Hz.This approach makes the supercontinuum spectra much easier to be generated than a single branch OFC.However,more out-of-loop fibers degrade the long-term frequency instability due to thermal drift.To minimize the thermal drift effect,we set the fiber lengths of different branches to be similar,and we stabilize the temperature as well.The out-of-loop frequency instability of the OFC due to the incoherence of the multi-branch is about5.5×10^(19) for 4000 s,while the in-loop frequency instability of fceo and that of fbeat are 7.5×10^(18) for 1 s and 8.5×10^(18) for 1 s,respectively.The turnkey OFC meets the requirement for the comparison of frequency between the best optical clocks.展开更多
Of all the units of physical science,one second is perhaps the most mysterious.Unlike a meter,we cannot see it.Unlike a kilogram,we cannot hold it in our hands.Unlike a volt,we have no nerves to sense it.Yet a second ...Of all the units of physical science,one second is perhaps the most mysterious.Unlike a meter,we cannot see it.Unlike a kilogram,we cannot hold it in our hands.Unlike a volt,we have no nerves to sense it.Yet a second is the most precisely quantified unit we have[1].This year,metrologists—scientists who study m easurem entannounced the first transportable clock that can measure time to 18 decimal places.To put this in perspective,a clock running with this precision since the Big Bang would have lost or gained less than half a second.展开更多
We propose a new ion-trap geometry to carry out accurate measurements of the quadrupole shifts in the (171)Yb ion.This trap will minimize the quadrupole shift due to the harmonic component of the confining potential...We propose a new ion-trap geometry to carry out accurate measurements of the quadrupole shifts in the (171)Yb ion.This trap will minimize the quadrupole shift due to the harmonic component of the confining potential by an order of magnitude.This will be useful to reduce the uncertainties in the clock frequency measurements of the 6s 2S(1/2)→4f(13)6s2 2F(7/2)and 6s 2S(1/2)→5d2D(3/2) transitions,from which we can deduce the precise values of the quadrupole moments(0s) of the 4f(13)6s2 2F(7/2) and 5d2D(3/2) states.Moreover,it may be able to affirm the validity of the measured 0 value of the4f(13)6s22F(7/2) state,for which three independent theoretical studies defer almost by one order of magnitude from the measurement.We also calculate 0s using the relativistic coupled-cluster(RCC) method.We use these 0 values to estimate the quadrupole shift that can be measured in our proposed ion trap experiment.展开更多
Due to high stable rotations, timing of pulsars provides a natural tool to correct the frequency deviation of spaceborne atomic clocks. Based on processing the observational data about a year of Crab pulsar given by X...Due to high stable rotations, timing of pulsars provides a natural tool to correct the frequency deviation of spaceborne atomic clocks. Based on processing the observational data about a year of Crab pulsar given by XPNAV-1 satellite, we study the possibility of correcting the frequency deviation of spaceborne atomic clocks using pulsar timing. According to the observational data in X-ray band and the timing model parameters from radio observations, the pre-fit timing residuals with a level of 67.66 μs are obtained. By fitting the slope of the timing residuals affected by the faked frequency-biased reference clock, we estimated successfully the relative frequency deviation of the reference clock. For a satellite clock with frequency deviation of the order about 10^(-12), a calibration accuracy with relative error of about 2% can be obtained from the Crab pulsar’s data for one year.The stability of the time scale based on Crab pulsar is about 10^(-12) for an interval of one year.展开更多
Circadian rhythm refers to the inherent 24-h cycle oscillation of biochemical,phys-iological and behavioral functions,which is almost universal in eukaryotes.At least 14 core clock genes have been reported to form mul...Circadian rhythm refers to the inherent 24-h cycle oscillation of biochemical,phys-iological and behavioral functions,which is almost universal in eukaryotes.At least 14 core clock genes have been reported to form multiple chain feedback loops that confer intrinsic circadian rhythmicity onto the molecular clock.Accumulating evidence has shown that the circadian gene dysfunction resulted from single nucleotide polymorphisms(SNPs),deletions,epigenetic modification,and deregulation is strongly associated with cancer risk.In the pre-sent review,we describe the composition of circadian rhythm system.We highlight the func-tion and mechanism of clock genes in cancer pathogenesis and progression.Moreover,their potential clinical implications as prognostic biomarkers and therapeutic targets have been ad-dressed.展开更多
基金supported by the National Natural Science Foundation of China under Grant 62034002 and 62374026.
文摘A frequency servo system-on-chip(FS-SoC)featuring output power stabilization technology is introduced in this study for high-precision and miniaturized cesium(Cs)atomic clocks.The proposed power stabilization loop(PSL)technique,incorporating an off-chip power detector(PD),ensures that the output power of the FS-SoC remains stable,mitigating the impact of power fluctuations on the atomic clock's stability.Additionally,a one-pulse-per-second(1PPS)is employed to syn-chronize the clock with GPS.Fabricated using 65 nm CMOS technology,the measured phase noise of the FS-SoC stands at-69.5 dBc/Hz@100 Hz offset and-83.9 dBc/Hz@1 kHz offset,accompanied by a power dissipation of 19.7 mW.The Cs atomic clock employing the proposed FS-SoC and PSL obtains an Allan deviation of 1.7×10^(-11) with 1-s averaging time.
基金Project supported by the Basic Frontier Science Research Program of Chinese Academy of Sciences (Grant No.ZDBS-LY-DQC028)the National Key Research and Development Program of China (Grant No.2017YFA0304404)the National Natural Science Foundation of China (Grant No.11674357)。
文摘We report an experimental demonstration of geopotential difference measurement using a pair of transportable ^(40)Ca^(+) optical clocks(TOC-729-1 and TOC-729-3)in the laboratory,each of them has an uncertainty of 1.3×10^(−17) and an instability of 4.8×10^(−15)/√τ.Referenced to a stationary clock of TOC-729-1,the geopotential difference measurements are realized by moving TOC-729-3 to three different locations and the relevant altitude differences are measured with uncertainties at the level of 20 cm.After correcting the systematic shifts(including gravitational red shift),the two-clock frequency difference is measured to be–0.7(2.2)×10^(−17),considering both the statistic(1.0×10^(−17))and the systematic(1.9×10^(−17))uncertainties.The frequency difference between these two clocks is within their respective uncertainties,verifying the reliability of transportable ^(40)Ca^(+) optical clocks at the low level of 10^(−17).
基金Project supported by the National Natural Science Foundation of China(Grant No.12173044)Research and Development Project of Scientific Research Instruments and Equipment of Chinese Academy of Sciences(Grant No.YJKYYQ20200020)+1 种基金Large Research Infrastructures Improvement Funds of Chinese Academy of Sciences(Grant No.DSS-WXGZ-2020-0005)Chinese Academy of Sciences for Western Young Scholars(Grant Nos.XAB2018A06,XAB2019A07,and XAB2018B16)。
文摘The caesium atomic fountain clock is a primary frequency standard.During its operation,a Majorana transition frequency shift will occur once a magnetic field at some special locations along the atomic trajectory is singular.In this study,by developing a physical model,we analyzed the magnetic field requirements for atomic adiabatic transition and calculated the influence of the Majorana atomic transition on the atomic state via a quantum method.Based on the simulation results for the magnetic field in the fountain clock,we applied the Monte Carlo method to simulate the relationship between the Majorana transition frequency shift and the magnetic field at the entrance of the magnetic shielding,as well as the initial atomic population.Measurement of the Majorana transition frequency shift was realized by state-selecting asymmetrically populated atoms.The relationship between the Majorana transition frequency shift and the axial magnetic field at the entrance of the magnetic shielding was obtained.The measured results were essentially consistent with the calculated results.Thus,the magnetic field at the entrance of the magnetic shielding was configured,and the Majorana transition frequency shift of the fountain clock was calculated to be 4.57×10^(-18).
基金Project supported by the National Natural Science Foundation of China (Grant No.61775220)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDB21030100)the Key Research Project of Frontier Science of the Chinese Academy of Sciences (Grant No.QYZDB-SSW-JSC004)。
文摘The study of magnetic field effects on the clock transition of Mg and Cd optical lattice clocks is scarce.In this work,the hyperfine-induced Landég-factors and quadratic Zeeman shift coefficients of the nsnp ^(3)P_(0)^(o) clock states for ^(111,113)Cd and ^(25)Mg were calculated by using the multi-configuration Dirac–Hartree–Fock theory.To obtain accurate values of these parameters,the impact of electron correlations and furthermore the Breit interaction and quantum electrodynamical effects on the Zeeman and hyperfine interaction matrix elements,and energy separations were investigated in detail.We also estimated the contributions from perturbing states to the Landég-factors and quadratic Zeeman shift coefficients concerned so as to truncate the summation over the perturbing states without loss of accuracy.Our calculations provide important data for estimating the first-and second-order Zeeman shifts of the clock transition for the Cd and Mg optical lattice clocks.
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Project supported by the National Key Basic Research and Development Program of China(Grant Nos.2016YFA0302103,2017YFF0212003,and 2016YFB0501601)the Municipal Science and Technology Major Project of Shanghai,China(Grant No.2019SHDZX01)+1 种基金the National Natural Science Foundation of China(Grant No.11134003)the Excellent Academic Leaders Program of Shanghai,China(Grant No.12XD1402400).
文摘The optical atomic clocks have the potential to transform global timekeeping,relying on the state-of-the-art accuracy and stability,and greatly improve the measurement precision for a wide range of scientific and technological applications.Herein we report on the development of the optical clock based on 171Yb atoms confined in an optical lattice.A minimum width of 1.92-Hz Rabi spectra has been obtained with a new 578-nm clock interrogation laser.The in-loop fractional instability of the 171Yb clock reaches 9.1×10-18 after an averaging over a time of 2.0×104 s.By synchronous comparison between two clocks,we demonstrate that our 171Yb optical lattice clock achieves a fractional instability of 4.60×10-16/√τ.
基金Supported by the National Basic Research Program of China under Grant No 2012CB821300the National Natural Science Foundation of China under Grant Nos 91336213,11304109,91536116 and 11174095the Program for New Century Excellent Talents by the Ministry of Education under Grant No NCET-11-0176
文摘The Al^+ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of AI+ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al^+ traps are utilized. The first trap is used to trap a large number of Al^+ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al^+ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167nm laser. The expected clock laser stability can reach 9.0 × 10^-17/√τ. For the second trap, in addition to 167nm laser Doppler cooling, a second stage pulsed 234nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about 1 × 10^-18. The proposed Al^+ ion optical clock has the potential to become the most accurate and stable optical clock.
文摘Foreign-made clocks and watches began to be exported to China in the 17th century. During the Qing Dynasty (1644-1911), the imperial court imported tens of thousands of clocks and watches. At the Palace Museum in Beijing, about 200 timepieces collected by the imperial court are still on display in the clock and watch exhibition hall. They were made in Britain, France, Switzerland and Japan. Many foreign presidents and
基金Project support by the National Natural Science Foundation of China(Grant No.11074012)
文摘Research on chip-scale atomic clocks (CSACs) based on coherent population trapping (CPT) is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the re- liability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance's collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research.
基金Project supported by the National Natural Science Foundation of China(Grant No.11873044)the National Key Research and Development Project of China(Grant No.2016YFF0200202)Consulting Research Project of Chinese Academy of Engineering(Grant No.2018-ZCQ-03)。
文摘Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in 1016, and the best optical clock has reached a type B uncertainty below 10-18. Besides applications in the metrology, navigation, etc.,ultra-stable and ultra-accurate atomic clocks have also become powerful tools in the basic scientific investigations. In this paper, we focus on the recent developments in the high-performance cold atomic clocks which can be used as frequency standards to calibrate atomic time scales. The basic principles, performances, and limitations of fountain clocks and optical clocks based on signal trapped ion or neutral atoms are summarized. Their applications in metrology and other areas are briefly introduced.
基金Project supported by National 863/973 Plans Projects (Grant Nos. 2006AA04Z361,2006CB932402)NSFC (Grant No. 60971002)
文摘We describe the microfabrication of ^85Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb. Under controlled conditions, the pure metallic Rb drops and buffer gases were obtained in the cells with a few mm^3 internal volumes during the cell sealing process. At an ambient temperature of 90 ℃ the optical absorption resonance of ^85Rb D1 transition with proper broadening and the corresponding coherent population trapping (CPT) resonance, with a signal contrast of 1.5% and linewidth of about 1.7 kHz, have been detected. The sealing quality and the stability of the cells have also been demonstrated experimentally by using the helium leaking detection and the after-9-month optoelectronics measurement which shows a similar CPT signal as its original status. In addition, the physics package of chip-scale atomic clock (CSAC) based on the cell was realized. The measured frequency stability of the physics package can reach to 2.1 × 10^-10 at one second when the cell was heated to 100 ℃ which proved that the cell has the quality to be used in portable and battery-operated devices.
基金supported by National Natural Science Foundation of China(NSFC)(grant Nos.41721003,41631072,41874023,41804012,41429401,41574007)Natural Science Foundation of Hubei Province(grant No.2019CFB611)
文摘General relativity theory(GRT)concludes that a precise clock ticks at different running rates if it is under the influence of different geopotentials.Therefore,by comparing the running rates of clocks at arbitrary two stations,the geopotential difference between them can be determined.In this study,with the help of two hydrogen atomic clocks(noted as H-masers),using the two-way satellite time and frequency transfer(TWSTFT)technique,we carried out experiments of the geopotential difference determination at the China Aerospace Science&Industry Corporation(CASIC),Beijing.Here the ensemble empirical mode decomposition(EEMD)method is adopted to remove periodic signals included in the original observations.Finally,the clock-comparison-determined geopotential difference in the experiments is determined.Results show that the difference between the geopotential difference determined by GRT and that determined by measuring tape is about 1316.1±931.0 m2s-2,which is equivalent to 134.3±95.0 m in height,and in consistence with the stability of the H-masers applied in the experiments(at the level of10-15/day).With the rapid improvement of atomic clocks’accuracy,the geopotential determination by accurate clocks is prospective,and it is promising to realize the unification of the world vertical height system(WVHS).
基金Project supported by the National Key Basic Research and Development Program of China(Grant Nos.2012CB821302 and 2016YFA0302103)the National Natural Science Foundation of China(Grant No.11134003)+1 种基金the National High Technology Research and Development Program of China(Grant No.2014AA123401)the Shanghai Excellent Academic Leaders Program of China(Grant No.12XD1402400)
文摘We develop a permanent-magnet Zeeman slower with adjustable magnets along the longitudinal and radial directions.Produced by four arrays of cylindrical magnets, the longitudinal magnetic field in the slower is tunable if relevant parameters vary, for example, laser detuning or intensity. The proposed Zeeman slower can be reconfigured for Sr atoms. Additionally,we demonstrate that the residual magnetic field produced by the permanent magnets in the magneto-optical trap region can be as small as 0.5 Gs.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11304362 and 11204351)
文摘A method that obtains the Ramsey-coherent population trapping (CPT) spectrum with the Faraday effect is investi- gated. An experiment is implemented to detect the light polarization components generated from the Faraday effect. The experimental results agree with the theoretical calculations based on the Liouville equation. By comparing with the method without using the Faraday effect, the potential of this method for a CPT-based atomic clock is assessed. The results indicate that this method should improve the short-term frequency stability by several times.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11604385 and 91536106)the Natural Science Foundation of Hunan Province,China(Grant No.2019JJ50743)the Research Project of the National University of Defense Technology(Grant No.ZK17-03-11)。
文摘Based on the multiconfiguration Dirac-Hartree-Fock(MCDHF)method,similar models are employed to simultaneously calculate the first-order and second-order Zeeman coefficients as well as the hyperfine interaction constants of the related energy levels of ^(27)Al^(+)and its logical ions ^(9)Be^(+)and^(25)Mg^(+)in the^(27)Al^(+)optical clock.With less than 0.34%deviations from experimental values in Zeeman coefficients of^(27)Al^(+),these calculated parameters will be of great help for better evaluation of the systematic uncertainty.We also calculate the isotope shift parameters of the related energy levels,which could extend our knowledge and understanding of nuclear properties of these ions.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB35030101)the National Natural Science Foundation of China(Grant No.61825505)+1 种基金the Quantum Control and Quantum Information of the National Key Research and Development Program of China(Grant No.2020YFA0309800)the Natural Science Basic Research Program of Shaanxi Province,China(Grant No.2020JQ434)。
文摘We demonstrate an optical frequency comb(OFC)based on a turnkey mode-locked laser with a figure-9-shape structure and polarization-maintaining fibers,for the comparison of frequency among optical clocks with wavelengths of 698 nm,729 nm,1068 nm,and 1156 nm.We adopt a multi-branch approach in order to produce high power OFC signals at these specific wavelengths,enabling the signal-to-noise ratio of the beatnotes between the OFC and the clock lasers to exceed30 d B at a resolution bandwidth of 300 k Hz.This approach makes the supercontinuum spectra much easier to be generated than a single branch OFC.However,more out-of-loop fibers degrade the long-term frequency instability due to thermal drift.To minimize the thermal drift effect,we set the fiber lengths of different branches to be similar,and we stabilize the temperature as well.The out-of-loop frequency instability of the OFC due to the incoherence of the multi-branch is about5.5×10^(19) for 4000 s,while the in-loop frequency instability of fceo and that of fbeat are 7.5×10^(18) for 1 s and 8.5×10^(18) for 1 s,respectively.The turnkey OFC meets the requirement for the comparison of frequency between the best optical clocks.
文摘Of all the units of physical science,one second is perhaps the most mysterious.Unlike a meter,we cannot see it.Unlike a kilogram,we cannot hold it in our hands.Unlike a volt,we have no nerves to sense it.Yet a second is the most precisely quantified unit we have[1].This year,metrologists—scientists who study m easurem entannounced the first transportable clock that can measure time to 18 decimal places.To put this in perspective,a clock running with this precision since the Big Bang would have lost or gained less than half a second.
基金CSIR-National Physical Laboratory,Depaitment of Science and Technology(Grant No.SB/S2/LOP/033/2013)the Board of Research in Nuclear Sciences(Grant No. 34/14/ 19/2014-BRNS/0309) for supporting
文摘We propose a new ion-trap geometry to carry out accurate measurements of the quadrupole shifts in the (171)Yb ion.This trap will minimize the quadrupole shift due to the harmonic component of the confining potential by an order of magnitude.This will be useful to reduce the uncertainties in the clock frequency measurements of the 6s 2S(1/2)→4f(13)6s2 2F(7/2)and 6s 2S(1/2)→5d2D(3/2) transitions,from which we can deduce the precise values of the quadrupole moments(0s) of the 4f(13)6s2 2F(7/2) and 5d2D(3/2) states.Moreover,it may be able to affirm the validity of the measured 0 value of the4f(13)6s22F(7/2) state,for which three independent theoretical studies defer almost by one order of magnitude from the measurement.We also calculate 0s using the relativistic coupled-cluster(RCC) method.We use these 0 values to estimate the quadrupole shift that can be measured in our proposed ion trap experiment.
基金supported by the National SKA Program of China(No.2020SKA0120103)the National Natural Science Foundation of China(Nos.U1831130 and U1531112).
文摘Due to high stable rotations, timing of pulsars provides a natural tool to correct the frequency deviation of spaceborne atomic clocks. Based on processing the observational data about a year of Crab pulsar given by XPNAV-1 satellite, we study the possibility of correcting the frequency deviation of spaceborne atomic clocks using pulsar timing. According to the observational data in X-ray band and the timing model parameters from radio observations, the pre-fit timing residuals with a level of 67.66 μs are obtained. By fitting the slope of the timing residuals affected by the faked frequency-biased reference clock, we estimated successfully the relative frequency deviation of the reference clock. For a satellite clock with frequency deviation of the order about 10^(-12), a calibration accuracy with relative error of about 2% can be obtained from the Crab pulsar’s data for one year.The stability of the time scale based on Crab pulsar is about 10^(-12) for an interval of one year.
基金supported by grants from the National Natural Science Foundation of China(No.81874195,82173144)the Natural Science Foundation of Hunan Province(No.2020JJ4769)+1 种基金the Fundamental Research Funds for the Central Universities of Central South University(No.2021zzts0925)the Open-End Fund for the Valuable and Precision Instruments of Central South University(No.CSUZC202237).
文摘Circadian rhythm refers to the inherent 24-h cycle oscillation of biochemical,phys-iological and behavioral functions,which is almost universal in eukaryotes.At least 14 core clock genes have been reported to form multiple chain feedback loops that confer intrinsic circadian rhythmicity onto the molecular clock.Accumulating evidence has shown that the circadian gene dysfunction resulted from single nucleotide polymorphisms(SNPs),deletions,epigenetic modification,and deregulation is strongly associated with cancer risk.In the pre-sent review,we describe the composition of circadian rhythm system.We highlight the func-tion and mechanism of clock genes in cancer pathogenesis and progression.Moreover,their potential clinical implications as prognostic biomarkers and therapeutic targets have been ad-dressed.