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B. Lipphardt

Publications and source records attributed to B. Lipphardt.

27 records · Page 2Linked to original sources
arXiv2012

High-accuracy optical clock based on the octupole transition in 171Yb+

We experimentally investigate an optical frequency standard based on the 467 nm (642 THz) electric-octupole reference transition 2S1/2(F=0) -> F7/2(F=3) in a single trapped 171Yb+ ion. The extraordinary features of this transition result from the long natural lifetime and from the 4f136s2 configuration of the upper state. The electric quadrupole moment of the 2F7/2 state is measured as -0.041(5) e(a0)^2, where e is the elementary charge and a0 the Bohr radius. We also obtain information on the differential scalar and tensorial components of the static polarizability and of the probe light induced ac Stark shift of the octupole transition. With a real-time extrapolation scheme that eliminates this shift, the unperturbed transition frequency is realized with a fractional uncertainty of 7.1x10^(-17). The frequency is measured as 642 121 496 772 645.15(52) Hz.

physics.atom-ph↗
arXiv2011

The 87-Sr optical frequency standard at PTB

With 87-Sr atoms confined in a one dimensional optical lattice, the frequency of the optical clock transition 5s^2 ^1S_0 - 5s5p ^3P_0 has been determined to be 429 228 004 229 872.9(5) Hz. The transition frequency was measured with the help of a fs-frequency comb against one of PTB's H-masers whose frequency was measured simultaneously by the PTB Cs fountain clock CSF1. The Sr optical frequency standard contributes with a fractional uncertainty of 1.5 10^-16 to the total uncertainty. The agreement of the measured transition frequency with previous measurements at other institutes supports the status of this transition as secondary representation of the second with the currently smallest uncertainty.

physics.atom-ph↗
arXiv2009

Optical frequency transfer via 146 km fiber link with 10^{-19} relative accuracy

We demonstrate the long-distance transmission of an ultra-stable optical frequency derived directly from a state-of-the-art optical frequency standard. Using an active stabilization system we deliver the frequency via a 146 km long underground fiber link with a fractional instability of 3*10^{-15} at 1 s, which is close to the theoretical limit for our transfer experiment. The relative uncertainty for the transfer is below 1*10^{-19} after 30 000 seconds. Tests with a very short fiber show that noise in our stabilization system contributes fluctuations which are two orders of magnitude lower, namely 3*10^{-17} at 1 s, reaching 10^{-20} after 4000 s.

physics.optics↗
arXiv2009

Interrogation of caesium atoms in a fountain clock by a femtosecond laser microwave oscillator

A caesium fountain clock is operated utilizing a microwave oscillator that derives its frequency stability from a stable laser by means of a fiber-laser femtosecond frequency comb. This oscillator is based on the technology developed for optical clocks and replaces the quartz based microwave oscillator commonly used in fountain clocks. As a result, a significant decrease of the frequency instability of the fountain clock is obtained, reaching 0.74E-14 at 100 s averaging time. We could demonstrate that for a significant range of detected atom numbers the instability is limited by quantum projection noise only, and that for the current status of this fountain clock the new microwave source poses no limit on the achievable frequency instability.

physics.atom-ph↗
arXiv2008

The stability of an optical clock laser transferred to the interrogation oscillator for a Cs fountain

We stabilise a microwave oscillator at 9.6 GHz to an optical clock laser at 344 THz by using a fibre-based femtosecond laser frequency comb as a transfer oscillator. With a second frequency comb we measure independently the instability of the microwave source with respect to another optical clock laser frequency at 456 THz. The total fractional frequency instability of this optic-to-microwave and microwave-to-optic conversion resulted in an Allan deviation sigma_y, of sigma_y=1.2E-14 at 1 s averaging time (band width 50 kHz). The residual phase noise density is -97 dBc/Hz at 10 Hz offset from the 9.6 GHz carrier. Replacing the existing quartz-based interrogation oscillator of the PTB caesium fountain CSF1 with this optically stabilised microwave source will reduce the instability contribution due to the Dick effect from the 1E-13-level at 1s averaging time to an insignificant level at the current status of CSF1. Therefore this new microwave source can be an alternative to cryogenic sapphire-loaded cavity oscillators in order to overcome the limitations of state-of-the-art quartz oscillators.

physics.atom-ph↗
arXiv2006

Laboratory Limits on Temporal Variations of Fundamental Constants: An Update

Precision comparisons of different atomic frequency standards over a period of a few years can be used for a sensitive search for temporal variations of fundamental constants. We present recent frequency measurements of the 688 THz transition in the $^{171}$Yb$^+$ ion. For this transition frequency a record over six years is now available, showing that a possible frequency drift relative to a cesium clock can be constrained to $(-0.54\pm0.97)$ Hz/yr, i.e. at the level of $2\cdot10^{-15}$ per year. Combined with precision frequency measurements of an optical frequency in $^{199}$Hg$^+$ and of the hyperfine ground state splitting in $^{87}$Rb a stringent limit on temporal variations of the fine structure constant $α$: $d\lnα/dt= (-0.26\pm0.39)\cdot 10^{-15} {\rm yr}^{-1}$ and a model-dependent limit for variations of the proton-to-electron mass ratio $μ$ in the present epoch can be derived: $d \ln μ/dt = (-1.2 \pm 2.2)\cdot 10^{-15} {\rm yr}^{-1}$. We discuss these results in the context of astrophysical observations that apparently indicate changes in both of these constants over the last 5--10 billion years.

physics.atom-ph↗
arXiv2005

Frequency comparisons and absolute frequency measurements of 171Yb+ single-ion optical frequency standards

We describe experiments with an optical frequency standard based on a laser cooled $^{171}$Yb$^+$ ion confined in a radiofrequency Paul trap. The electric-quadrupole transition from the $^2S_{1/2}(F=0)$ ground state to the $^2D_{3/2}(F=2)$ state at the wavelength of 436 nm is used as the reference transition. In order to compare two $^{171}$Yb$^+$ standards, separate frequency servo systems are employed to stabilize two probe laser frequencies to the reference transition line centers of two independently stored ions. The experimental results indicate a relative instability (Allan standard deviation) of the optical frequency difference between the two systems of $σ_y(1000 {\rm s})=5\cdot 10^{-16}$ only, so that shifts in the sub-hertz range can be resolved. Shifts of several hertz are observed if a stationary electric field gradient is superimposed on the radiofrequency trap field. The absolute optical transition frequency of Yb$^+$ at 688 THz was measured with a cesium atomic clock at two times separated by 2.8 years. A temporal variation of this frequency can be excluded within a $1σ$ relative uncertainty of $4.4\cdot 10^{-15}$ yr$^{-1}$. Combined with recently published values for the constancy of other transition frequencies this measurement provides a limit on the present variability of the fine structure constant $α$ at the level of $2.0\cdot 10^{-15}$ yr$^{-1}$.

physics.atom-ph↗
arXiv2004

New limit on the present temporal variation of the fine structure constant

The comparison of different atomic transition frequencies over time can be used to determine the present value of the temporal derivative of the fine structure constant alpha in a model-independent way without assumptions on constancy or variability of other parameters. We have measured an optical transition frequency at 688 THz in ^{171}Yb+ with a cesium atomic clock at two times separated by 2.8 years and find a value for the fractional variation of the frequency ratio $f_{\rm Yb}/f_{\rm Cs}$ of $(-1.2\pm 4.4)\cdot 10^{-15}$ yr$^{-1}$, consistent with zero. Combined with recently published values for the constancy of other transition frequencies this measurement sets an upper limit on the present variability of alpha at the level of $2.0\cdot 10^{-15}$ yr$^{-1}$, corresponding so far to the most stringent limit from laboratory experiments.

physics.atom-ph↗