摘要:

©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354336

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

This paper reviews recent progress on microwave clocks using laser cooled neutral atoms. With an ultra-stable cryogenic sapphire oscillator as interrogation oscillator, a cesium fountain operates at the quantum projection noise limit. With6 105detected atoms, the relative frequency stability &dgr;&ngr;/&ngr; is4 10−14&tgr;−1/2where &tgr; is the integration time in seconds. This stability is comparable to that of hydrogen masers. At&tgr;=2 104&hthinsp;s,the measured stability reaches6 10−16.Equally important is the accuracy of the frequency standard since133Csis the primary reference for the definition of the time unit, the second. The accuracy of our cesium fountain FO1 is presently1 10−15,currently the best reported value.A87Rbfountain has also been constructed and the87Rbground-state hyperfine energy has been compared to the Cs primary standard with a relative accuracy of2.5 10−15.Comparing the hyperfine energies of atoms with different atomic numbersZ, one can search for possible variations of the fine structure constant&agr;=e2/ℏcwith time. Measurements of the ratio&ngr;(87Rb)/&ngr;(133Cs)spread over an interval of 24 months indicate no change at a level of3.1 10−15/year,placing a new upper limit for1/&agr;(d&agr;/dt).The second attractive feature of87Rbfountains is the smallness of the frequency shift induced by the mean field interaction between atoms. This shift is found to be at least ∼50 times below that of cesium.Finally, the interest of the microgravity of space for cold atom experiments is out-lined. A space mission, ACES, carrying ultra-stable clocks, is presented. ACES has been selected by the European Space Agency to fly on the International Space Station in 2004. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354337

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We review our progress in a measurement ofℏ/MCs.Using an atom interferometer method based on adiabatic transfer between atomic states, we measure the recoil velocity of cesium due to the scattering of a photon. Our current statistical uncertainty is on the order of 3 parts per billion inℏ/MCs.This paper will summarize our current status in dealing with the systematic effects of this measurement. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354338

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Optical frequency metrology plays an important role for the determination of the Rydberg constant and offers an alternative way to determine the fine structure constant &agr;. We have developed a new technique for measuring optical frequencies using femtosecond light pulses culminating in the single laser optical frequency synthesizer. This new technique greatly simplifies the task of measuring optical frequencies. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354339

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Using a Penning trap single ion mass spectrometer, we have measured the atomic masses of 13 isotopes, many important for fundamental metrology and fundamental constants. The accuracy of the measurements,≈10−10,is typically two orders of magnitude better than previously accepted values. A wide variety of self consistency checks greatly reduces the possibility of unknown systematic errors.As part of a program to determine the Molar Planck constantNAhand the fine structure constant &agr;, we measured the masses of133Cs,87,85Rb,and23Na.Our high accuracy atomic mass measurements can be combined with values ofh/matomfrom atom interferometry measurements and accurate wavelength measurements for different atoms to give several independent determinations ofNAhand &agr;. This route to &agr; throughNAh,the atomic mass of the protonMp,the electron to proton mass ratiome/mp,and the Rydberg constantR∞is based on simple physics. It can potentially achieve the several ppb accuracy needed to test the QED determination of &agr; extracted from measurements of the electron g factor. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354340

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Theories unifying gravity and other interactions predict spatial and temporal variation of physical “constants” in the Universe. Comparison of quasar absorption line spectra with laboratory spectra provide the best probe for variability of the fine structure constant,&agr;=e2/ℏc,over cosmological time-scales. We have demonstrated [1] that high sensitivity to the variation of &agr; can be obtained from a comparison of the spectra of heavy and light atoms and have obtained an order of magnitude gain in precision over previous methods [2]. Our new constraints [3] on &agr; come from simultaneous fitting of numerous absorption lines of the following species: MgI, MgII, AlII, AlIII, SiII, CrII, FeII, NiIIand ZnII. The results are based on an analysis of 49 absorption systems covering cosmological time starting from about 10&percent; of the age of the Universe after Big Bang (the redshift parameters cover0.5<z<3.5). The data containstatisticalevidence for a smaller &agr; at earlier epochs at the 4.3&sgr; level. We briefly discuss possible systematic errors and numerous tests done to estimate and reduce these errors. Careful searches have so far not revealed any spurious effect that can explain the observations. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354341

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354342

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Quantum jumps between Fock states of a one-electron oscillator reveal the quantum limit of a cyclotron accelerator. The states live for seconds when spontaneous emission is inhibited by 140 within a cylindrical Penning trap cavity. Averaged over hours the oscillator is in thermal equilibrium with black-body photons in the cavity. At 80 mK, quantum jumps occur only when resonant microwave photons are introduced into the cavity, opening a route to improved measurements of the magnetic moments of the electron and positron. The temperature demonstrated is about 60 times lower than the 4.2 K temperature at which charged elementary particles were previously stored. Implications for the production of cold antihydrogen are discussed. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354343

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The linear Stark effect on a single molecule allows us to sweep its frequency through resonance with a fixed laser frequency by applying a sinusoidal RF voltage on two electrodes. If the conditions of adiabatic following are fulfilled, we can prepare the excited molecular state with near certainty. Spontaneous emission from this state gives rise to a single photon. With our current experimental conditions, up to 75&percent; of the sweeps lead to the emission of a single photon. Since the adiabatic passage is done on command, the molecule performs as a high rate source of triggered photons. The experimental results are in quantitative agreement with quantum Monte Carlo simulations. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354344

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Ground state cooling and coherent manipulation of ions in an rf-(Paul) trap is the prerequisite for quantum information experiments with trapped ions. With resolved sideband cooling on the opticalS1/2−D5/2quadrupole transition we have cooled one and two40Ca+ions to the ground state of vibration with up to 99.9&percent; probability. With a novel cooling scheme utilizing electromagnetically induced transparency on theS1/2−P1/2manifold we have achieved simultaneous ground state cooling of two motional sidebands 1.7 MHz apart. Starting from the motional ground state we have demonstrated coherent quantum state manipulation on theS1/2−D5/2quadrupole transition at 729 nm. Up to 30 Rabi oscillations within 1.4 ms have been observed in the motional ground state and in then=1Fock state. In the linear quadrupole rf-trap with 700 kHz trap frequency along the symmetry axis (2 MHz in radial direction) the minimum ion spacing is more than 5 &mgr;m for up to 4 ions. We are able to cool two ions to the ground state in the trap and individually address the ions with laser pulses through a special optical addressing channel. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1354345

出版商:AIP    

年代:1901

数据来源: AIP