Laser-cooled atoms - Toward an ultrastable cesium clock

Optical atomic clocks with fractional uncertainties around and below 10−17 [1] and fractional instabilities at one second interrogation time of below 10−15 [2] have outperformed the best microwave clocks like the cesium atomic clock. In optical atomic clocks a highly stable laser is used to interrogate optical transitions in laser-cooled atoms, ions, or molecules. The increase in accuracy and stability of the optical atomic clocks results from the increased line quality factor Q= ν/Δν given by the five orders of magnitude higher frequency of optical transitions as compared to the transition relevant in the microwave domain. To utilize this potential it is furthermore necessary to realize a suitable narrow linewidth of the interrogated line. The linewidth of any optical transition is given by the different broadening mechanisms of the respective quantum transition relevant for particular interrogation process as well as by the coherence properties of the interrogating laser.Optical atomic clocks with fractional uncertainties around and below 10−17 [1] and fractional instabilities at one second interrogation time of below 10−15 [2] have outperformed the best microwave clocks like the cesium atomic clock. In optical atomic clocks a highly stable laser is used to interrogate optical transitions in laser-cooled atoms, ions, or molecules. The increase in accuracy and stability of the optical atomic clocks results from the increased line quality factor Q= ν/Δν given by the five orders of magnitude higher frequency of optical transitions as compared to the transition relevant in the microwave domain. To utilize this potential it is furthermore necessary to realize a suitable narrow linewidth of the interrogated line. The linewidth of any optical transition is given by the different broadening mechanisms of the respective quantum transition relevant for particular interrogation process as well as by the coherence properties of the interrogating laser.

Frontiers in OpticsJan 1, 20131 citation

Quantum Projection Noise in an Atomic Fountain: A High Stability Cesium Frequency Standard

Giorgio Santarelli, Philippe Laurent, P. Lemonde +5 more

We describe the operation of a laser cooled cesium fountain clock in the quantum limited regime. An ultrastable cryogenic sapphire oscillator is used to measure the short-term frequency stability of the fountain as a function of the number of detected atoms ${N}_{\mathrm{at}}$ . For ${N}_{\mathrm{at}}$ varying from $4\ifmmode\times\else\texttimes\fi{}{10}^{4}$ to $6\ifmmode\times\else\texttimes\fi{}{10}^{5}$ the Allan standard deviation of the frequency fluctuations is in excellent agreement with the ${N}_{\mathrm{at}}^{\ensuremath{-}1/2}$ law of atomic projection noise. With $6\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms, the relative frequency stability is $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\ensuremath{\tau}}^{\ensuremath{-}1/2}$, where \ensuremath{\tau} is the integration time in seconds. This is the best short-term stability ever reported for primary frequency standards, a factor of 5 improvement over previous results.We describe the operation of a laser cooled cesium fountain clock in the quantum limited regime. An ultrastable cryogenic sapphire oscillator is used to measure the short-term frequency stability of the fountain as a function of the number of detected atoms ${N}_{\mathrm{at}}$. For ${N}_{\mathrm{at}}$ varying from $4\ifmmode\times\else\texttimes\fi{}{10}^{4}$ to $6\ifmmode\times\else\texttimes\fi{}{10}^{5}$ the Allan standard deviation of the frequency fluctuations is in excellent agreement with the ${N}_{\mathrm{at}}^{\ensuremath{-}1/2}$ law of atomic projection noise. With $6\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms, the relative frequency stability is $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\ensuremath{\tau}}^{\ensuremath{-}1/2}$, where \ensuremath{\tau} is the integration time in seconds. This is the best short-term stability ever reported for primary frequency standards, a factor of 5 improvement over previous results.

Physical Review LettersJun 7, 1999568 citations

Laser Cooling and Trapping of Cesium Atoms

Muhammad Naeem Anwar

Jan 1, 20160 citations

{N}_{\mathrm{at}}

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{N}_{\mathrm{at}}

varying from $4\ifmmode\times\else\texttimes\fi{}{10}^{4}$ to $6\ifmmode\times\else\texttimes\fi{}{10}^{5}$ the Allan standard deviation of the frequency fluctuations is in excellent agreement with the ${N}_{\mathrm{at}}^{\ensuremath{-}1/2}$ law of atomic projection noise. With $6\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms, the relative frequency stability is $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\ensuremath{\tau}}^{\ensuremath{-}1/2}$, where \ensuremath{\tau} is the integration time in seconds. This is the best short-term stability ever reported for primary frequency standards, a factor of 5 improvement over previous results.