Ruoxin Li - Academia.edu (original) (raw)
Papers by Ruoxin Li
Metrologia, 2012
We evaluate the frequency error from distributed cavity phase in the caesium fountain clock PTB-C... more We evaluate the frequency error from distributed cavity phase in the caesium fountain clock PTB-CSF2 at the Physikalisch-Technische Bundesanstalt with a combination of frequency measurements and ab initio calculations. The associated uncertainty is 1.3E-16, with a frequency bias of 0.4E-16. The agreement between the measurements and calculations explains the previously observed frequency shifts at elevated microwave amplitude. We also evaluate the frequency bias and uncertainty due to the microwave lensing of the atomic wavepackets. We report a total PTB-CSF2 systematic uncertainty of 4.1E-16.
We report measurements and ab initio calculations of the distributed cavity phase (DCP) shifts of... more We report measurements and ab initio calculations of the distributed cavity phase (DCP) shifts of the LNE-SYRTE FO2 atomic fountain clock. The measurements and validated model provide the first complete and quantitative evaluation of the DCP shift in an atomic fountain, reducing the FO2 DCP uncertainty to ±8.4x10 -17 . Here we emphasize the experimental
Metrologia, 2011
We discuss the treatment of distributed cavity phase, microwave lensing and microwave leakage in ... more We discuss the treatment of distributed cavity phase, microwave lensing and microwave leakage in the paper by Ovchinnikov and Marra (2011 Metrologia 48 87-100). The paper neglects the potential distributed cavity phase shifts from linear phase gradients and quadrupolar phase variations. Only azimuthally symmetric phase variations were analysed and an incorrect model was used for these. The paper also omits an uncertainty due to microwave lensing, which must be included. Finally, we describe additional measurements that could clarify the model used to analyse the frequency shifts due to microwave leakage.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2012
We give an overview of the work done with the LNE-SYRTE fountain ensemble during the last five ye... more We give an overview of the work done with the LNE-SYRTE fountain ensemble during the last five years. After a description of the clock ensemble, comprising three fountains FO1, FO2 and FOM, and its newest developments, we review recent studies of several systematic frequency shifts. This includes the distributed cavity phase shift which we evaluate for the FO1 and FOM fountains, applying the techniques of our recent work on FO2. We also report calculations of the microwave lensing frequency shift for the three fountains, review the status of the blackbody radiation shift, and summarize recent experimental work to control microwave leakage and spurious phase perturbations. We give current accuracy budgets. We also describe several applications in time and frequency metrology: fountain comparisons, calibrations of the international atomic time, secondary representation of the SI second based on the 87 Rb hyperfine frequency, absolute measurements of optical frequencies, tests of the T2L2 satellite laser link, and review fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally, we give a summary of the tests of the PHARAO cold atom space clock performed using the FOM transportable fountain.
Metrologia, 2011
We evaluate the distributed cavity phase and microwave lensing frequency shifts, which were the t... more We evaluate the distributed cavity phase and microwave lensing frequency shifts, which were the two largest sources of uncertainty for the NPL-CsF2 cesium fountain clock. We report measurements that confirm a detailed theoretical model of the microwave cavity fields and the frequency shifts of the clock that they produce. The model and measurements significantly reduce the distributed cavity phase uncertainty to 1.1times10−161.1 \times 10^{-16}1.1times10−16. We derive the microwave lensing frequency shift for a cylindrical cavity with circular apertures. An analytic result with reasonable approximations is given, in addition to a full calculation that indicates a shift of 6.2times10−176.2 \times 10^{-17}6.2times10−17. The measurements and theoretical models we report, along with improved evaluations of collisional and microwave leakage induced frequency shifts, reduce the frequency uncertainty of the NPL-CsF2 standard to 2.3times10−162.3 \times 10^{-16}2.3times10−16, nearly a factor of two lower than its most recent complete evaluation.
Physical Review Letters, 2011
We demonstrate agreement between measurements and ab initio calculations of the frequency shifts ... more We demonstrate agreement between measurements and ab initio calculations of the frequency shifts caused by distributed cavity phase variations in the microwave cavity of a primary atomic fountain clock. Experimental verification of the finite element models of the cavities gives the first quantitative evaluation of this leading uncertainty and allows it to be reduced to δν/ν=±8.4×10-17. Applying these experimental techniques to clocks with improved microwave cavities will yield negligible distributed cavity phase uncertainties, less than ±1×10-17.
We discuss the power dependence of distributed cavity phase errors for cylindrical TE 011 cavitie... more We discuss the power dependence of distributed cavity phase errors for cylindrical TE 011 cavities in laser-cooled atomic fountain clocks. The azimuthally symmetric phase variations produce a surprisingly large distributed cavity phase error for two 2π, 4π, and 6π pulses. This is due to the correlation between the transverse variation of the Rabi frequency over the cavity aperture and a quadratic density variation of the atomic sample, along with the symmetry of the longitudinal phase variation in the cavity. We show that the large azimuthally symmetric fields and phase shifts near the walls of the endcap holes produce very small errors at optimal power for a uniform wall resistance. We also show the power variation for higher order azimuthal variations m=1, 2, and 4. These may be caused by fountain tilts, non-uniform detection of atoms, and asymmetries in the laser trapping and cooling of the atoms. We demonstrate that distributed cavity phase errors in physical cavities may have no variation with the microwave power. A combination of rigorous calculations of cavity losses, measurements of power dependence, the atomic distributions, and fountain tilts, and electrical measurements that show the lower limit of the cavity Q and the cavity symmetry, should provide stringent limits on distributed cavity phase errors for current atomic clocks.
We have demonstrated a juggling /sup 87/Rb fountain clock. The juggling frequency shift is a part... more We have demonstrated a juggling /sup 87/Rb fountain clock. The juggling frequency shift is a particularly interesting measurement. We expect to report measurements of the Ramsey fringe contrast and a comparison to calculations that include photon recoils. We will also present results of calculations of distributed cavity phase shifts.
Examines cylindrical TE011 microwave cavities and finds large phase shifts of the microwave field... more Examines cylindrical TE011 microwave cavities and finds large phase shifts of the microwave field near the edges of the cut-off waveguide apertures, where there are nodes in the field. The phase shifts lead to a potential distributed cavity phase shift for atomic clocks. Using an additional larger diameter cut-off waveguide section can effectively exclude the nodes and the large phase shifts from the atomic trajectories. It has been suggested that recoils from the absorption of microwave photons lead to frequency shift and also a loss of fringe contrast. We present measurements of the contrast for up to 2 19π/2 pulses and find no loss of contrast beyond that expected from measuring microwave field inhomogeneities with up to 19π Rabi pulses.
Metrologia, 2010
We perform 3D finite element calculations of the fields in microwave cavities and analyze the dis... more We perform 3D finite element calculations of the fields in microwave cavities and analyze the distributed cavity phase errors of atomic clocks that they produce. The fields of cylindrical cavities are treated as an azimuthal Fourier series. Each of the lowest components produces clock errors with unique characteristics that must be assessed to establish a clock's accuracy. We describe the errors and how to evaluate them. We prove that sharp structures in the cavity do not produce large frequency errors, even at moderately high powers, provided the atomic density varies slowly. We model the amplitude and phase imbalances of the feeds. For larger couplings, these can lead to increased phase errors. We show that phase imbalances produce a novel distributed cavity phase error that depends on the cavity detuning. We also design improved cavities by optimizing the geometry and tuning the mode spectrum so that there are negligible phase variations, allowing this source of systematic error to be dramatically reduced.
Presented is quantitative evaluation of two leading uncertainties in the NPL-CsF2 fountain freque... more Presented is quantitative evaluation of two leading uncertainties in the NPL-CsF2 fountain frequency standard. The distributed cavity phase shift evaluation is based on recent theoretical model where the cavity field is decomposed into a series of 2D Fourier components in azimuthal angle in the cylindrical cavity. Predictions of the model are reproduced experimentally. The microwave lensing effect is caused by
We report measurements and calculations of distributed cavity phase errors in an atomic fountain ... more We report measurements and calculations of distributed cavity phase errors in an atomic fountain clock. We isolate even and odd symmetry contributions to the distributed cavity phase shift and measure their characteristic power dependences. The measurements and model largely agree with no free parameters. Verification of the model will enable a reduction of the distributed cavity phase uncertainty for current clocks and validates new cavity designs that have minimal phase variations.
Metrologia, 2012
We evaluate the frequency error from distributed cavity phase in the caesium fountain clock PTB-C... more We evaluate the frequency error from distributed cavity phase in the caesium fountain clock PTB-CSF2 at the Physikalisch-Technische Bundesanstalt with a combination of frequency measurements and ab initio calculations. The associated uncertainty is 1.3E-16, with a frequency bias of 0.4E-16. The agreement between the measurements and calculations explains the previously observed frequency shifts at elevated microwave amplitude. We also evaluate the frequency bias and uncertainty due to the microwave lensing of the atomic wavepackets. We report a total PTB-CSF2 systematic uncertainty of 4.1E-16.
We report measurements and ab initio calculations of the distributed cavity phase (DCP) shifts of... more We report measurements and ab initio calculations of the distributed cavity phase (DCP) shifts of the LNE-SYRTE FO2 atomic fountain clock. The measurements and validated model provide the first complete and quantitative evaluation of the DCP shift in an atomic fountain, reducing the FO2 DCP uncertainty to ±8.4x10 -17 . Here we emphasize the experimental
Metrologia, 2011
We discuss the treatment of distributed cavity phase, microwave lensing and microwave leakage in ... more We discuss the treatment of distributed cavity phase, microwave lensing and microwave leakage in the paper by Ovchinnikov and Marra (2011 Metrologia 48 87-100). The paper neglects the potential distributed cavity phase shifts from linear phase gradients and quadrupolar phase variations. Only azimuthally symmetric phase variations were analysed and an incorrect model was used for these. The paper also omits an uncertainty due to microwave lensing, which must be included. Finally, we describe additional measurements that could clarify the model used to analyse the frequency shifts due to microwave leakage.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2012
We give an overview of the work done with the LNE-SYRTE fountain ensemble during the last five ye... more We give an overview of the work done with the LNE-SYRTE fountain ensemble during the last five years. After a description of the clock ensemble, comprising three fountains FO1, FO2 and FOM, and its newest developments, we review recent studies of several systematic frequency shifts. This includes the distributed cavity phase shift which we evaluate for the FO1 and FOM fountains, applying the techniques of our recent work on FO2. We also report calculations of the microwave lensing frequency shift for the three fountains, review the status of the blackbody radiation shift, and summarize recent experimental work to control microwave leakage and spurious phase perturbations. We give current accuracy budgets. We also describe several applications in time and frequency metrology: fountain comparisons, calibrations of the international atomic time, secondary representation of the SI second based on the 87 Rb hyperfine frequency, absolute measurements of optical frequencies, tests of the T2L2 satellite laser link, and review fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally, we give a summary of the tests of the PHARAO cold atom space clock performed using the FOM transportable fountain.
Metrologia, 2011
We evaluate the distributed cavity phase and microwave lensing frequency shifts, which were the t... more We evaluate the distributed cavity phase and microwave lensing frequency shifts, which were the two largest sources of uncertainty for the NPL-CsF2 cesium fountain clock. We report measurements that confirm a detailed theoretical model of the microwave cavity fields and the frequency shifts of the clock that they produce. The model and measurements significantly reduce the distributed cavity phase uncertainty to 1.1times10−161.1 \times 10^{-16}1.1times10−16. We derive the microwave lensing frequency shift for a cylindrical cavity with circular apertures. An analytic result with reasonable approximations is given, in addition to a full calculation that indicates a shift of 6.2times10−176.2 \times 10^{-17}6.2times10−17. The measurements and theoretical models we report, along with improved evaluations of collisional and microwave leakage induced frequency shifts, reduce the frequency uncertainty of the NPL-CsF2 standard to 2.3times10−162.3 \times 10^{-16}2.3times10−16, nearly a factor of two lower than its most recent complete evaluation.
Physical Review Letters, 2011
We demonstrate agreement between measurements and ab initio calculations of the frequency shifts ... more We demonstrate agreement between measurements and ab initio calculations of the frequency shifts caused by distributed cavity phase variations in the microwave cavity of a primary atomic fountain clock. Experimental verification of the finite element models of the cavities gives the first quantitative evaluation of this leading uncertainty and allows it to be reduced to δν/ν=±8.4×10-17. Applying these experimental techniques to clocks with improved microwave cavities will yield negligible distributed cavity phase uncertainties, less than ±1×10-17.
We discuss the power dependence of distributed cavity phase errors for cylindrical TE 011 cavitie... more We discuss the power dependence of distributed cavity phase errors for cylindrical TE 011 cavities in laser-cooled atomic fountain clocks. The azimuthally symmetric phase variations produce a surprisingly large distributed cavity phase error for two 2π, 4π, and 6π pulses. This is due to the correlation between the transverse variation of the Rabi frequency over the cavity aperture and a quadratic density variation of the atomic sample, along with the symmetry of the longitudinal phase variation in the cavity. We show that the large azimuthally symmetric fields and phase shifts near the walls of the endcap holes produce very small errors at optimal power for a uniform wall resistance. We also show the power variation for higher order azimuthal variations m=1, 2, and 4. These may be caused by fountain tilts, non-uniform detection of atoms, and asymmetries in the laser trapping and cooling of the atoms. We demonstrate that distributed cavity phase errors in physical cavities may have no variation with the microwave power. A combination of rigorous calculations of cavity losses, measurements of power dependence, the atomic distributions, and fountain tilts, and electrical measurements that show the lower limit of the cavity Q and the cavity symmetry, should provide stringent limits on distributed cavity phase errors for current atomic clocks.
We have demonstrated a juggling /sup 87/Rb fountain clock. The juggling frequency shift is a part... more We have demonstrated a juggling /sup 87/Rb fountain clock. The juggling frequency shift is a particularly interesting measurement. We expect to report measurements of the Ramsey fringe contrast and a comparison to calculations that include photon recoils. We will also present results of calculations of distributed cavity phase shifts.
Examines cylindrical TE011 microwave cavities and finds large phase shifts of the microwave field... more Examines cylindrical TE011 microwave cavities and finds large phase shifts of the microwave field near the edges of the cut-off waveguide apertures, where there are nodes in the field. The phase shifts lead to a potential distributed cavity phase shift for atomic clocks. Using an additional larger diameter cut-off waveguide section can effectively exclude the nodes and the large phase shifts from the atomic trajectories. It has been suggested that recoils from the absorption of microwave photons lead to frequency shift and also a loss of fringe contrast. We present measurements of the contrast for up to 2 19π/2 pulses and find no loss of contrast beyond that expected from measuring microwave field inhomogeneities with up to 19π Rabi pulses.
Metrologia, 2010
We perform 3D finite element calculations of the fields in microwave cavities and analyze the dis... more We perform 3D finite element calculations of the fields in microwave cavities and analyze the distributed cavity phase errors of atomic clocks that they produce. The fields of cylindrical cavities are treated as an azimuthal Fourier series. Each of the lowest components produces clock errors with unique characteristics that must be assessed to establish a clock's accuracy. We describe the errors and how to evaluate them. We prove that sharp structures in the cavity do not produce large frequency errors, even at moderately high powers, provided the atomic density varies slowly. We model the amplitude and phase imbalances of the feeds. For larger couplings, these can lead to increased phase errors. We show that phase imbalances produce a novel distributed cavity phase error that depends on the cavity detuning. We also design improved cavities by optimizing the geometry and tuning the mode spectrum so that there are negligible phase variations, allowing this source of systematic error to be dramatically reduced.
Presented is quantitative evaluation of two leading uncertainties in the NPL-CsF2 fountain freque... more Presented is quantitative evaluation of two leading uncertainties in the NPL-CsF2 fountain frequency standard. The distributed cavity phase shift evaluation is based on recent theoretical model where the cavity field is decomposed into a series of 2D Fourier components in azimuthal angle in the cylindrical cavity. Predictions of the model are reproduced experimentally. The microwave lensing effect is caused by
We report measurements and calculations of distributed cavity phase errors in an atomic fountain ... more We report measurements and calculations of distributed cavity phase errors in an atomic fountain clock. We isolate even and odd symmetry contributions to the distributed cavity phase shift and measure their characteristic power dependences. The measurements and model largely agree with no free parameters. Verification of the model will enable a reduction of the distributed cavity phase uncertainty for current clocks and validates new cavity designs that have minimal phase variations.