Optical clock with ultracold neutral atoms

We demonstrate how to realize an optical clock with neutral atoms that is competitive to the currently best single ion optical clocks in accuracy and superior in stability. Using ultracold atoms in a Ca optical frequency standard, we show how to reduce the relative uncertainty to below 10(-15). We observed atom interferences for stabilization of the laser to the clock transition with a visibility of 0.36, which is 70% of the ultimate limit achievable with atoms at rest. A novel scheme was applied to detect these atom interferences with the prospect to reach the quantum projection noise limit at an exceptional low instability of 4 x 10(-17) in 1 s.     

Interferometry with Ca atoms

Separated field excitation of a calcium atomic beam using four traveling laser fields represents two distinct atom interferometers utilizing the internal degrees of freedom of the atoms. Phase shifts between the atomic partial waves have been realized by phase shifts of the laser wave fields, by the ac-Stark shift, and by rotation of the interferometer (Sagnac effect). One particular interferometer can be selected by interaction of the atomic waves with extra laser fields. We furthermore report on the preparation of a laser cooled and deflected calcium atomic beam that can be utilized to largely increase the sensitivity of the interferometer.     

Improvement of the fractional uncertainty of a neutral-atom calcium optical frequency standard to 2×10-14

We have investigated the two major effects that limit the accuracy of an optical frequency standard based on laser-cooled neutral calcium atoms, i.e. the residual Doppler shift and atomic collisions. A new correction method was applied to reduce the contribution of the residual Doppler effect to the total fractional uncertainty to 1×10^-14. Measurements of the shift of the clock transition frequency due to cold collisions allowed us to reduce their contribution to 4×10^-15. With these improvements we have reduced the total fractional frequency uncertainty of the standard by nearly an order of magnitude to 2×10^-14. Received: 9 August 2002 / Revised version: 16 November 2002 / Published online: 26 February 2003 RID="*" ID="*"Permanent address: Russian Academy of Sciences, P.N. Lebedev Physical Institute, Samara Branch, Novo-Sadovaya st. 221, Samara 443011, Russia RID="**" ID="**"Corresponding author. Fax: +49-531/592-4305, E-mail: uwe.sterr@ptb.de     

High-resolution spectroscopy with laser-cooled and trapped calcium atoms

We report on high-resolution spectroscopy with two different samples of calcium atoms, in a laser-cooled and deflected beam and in a magneto-optical trap. The atomic beam was excited by spatially separated laser fields. For spectroscopy with stored atoms in a magneto-optical trap we used a multiple-pulse excitation scheme. The resolution as low as 2.5 kHz was limited by residual frequency fluctuations of our dye-laser spectrometer. The results should allow to establish a frequency standard with a relative uncertainty below 10^–14.     

Polarization properties and frequency stabilization of an internal mirror He-Ne laser emitting at 543.5 nm wavelength

Frequency stabilization to the gain profile of an internal mirror He–Ne laser emitting at 543.5 nm wavelength is described. The dependence of the power and polarization on frequency was investigated for multi-mode and two-mode operation. The emitted laser modes are linearly polarized. Two orthogonal eigenpolarizations fixed to the laser tube were observed. Spontaneous switching between these polarizations occurred when the laser frequency was scanning through the gain profile. In two-mode operation, these polarization flips have been suppressed by applying a weak magnetic field transversal to the gas discharge. Under such operation conditions the frequencies of the laser could be stabilized to the gain profile by controlling the power difference of the two modes to zero. The fractional frequency reproducibility is in the region of f/f3×10^–8.     

Atom interferometry in a static electric field: Measurement of the Aharonov-Casher phase

Consecutive, phase-coherent, near-resonant optical excitations of atoms have been used to realize an atom interferometer with a beam of thermal calcium atoms. We have measured the topological phase shift due to the interaction of a static electric field with the magnetic dipole moment of a moving atom (Aharonov-Casher effect). The observed phase shift was proportional to the electric field and, within our experimental uncertainty, independent of the particle's velocity. The measured value of the phase shift has been found to agree with the predicted one within a relative uncertainty of 2.2%.Dedicated to H. Walther on the occasion of his 60th birthday