Quantum technologies

1999

• A. Nagel, S. Brandt, D. Meschede and R. Wynands
  Light shift of coherent population trapping resonances, Europhys. Lett. 48, 385-389 (1999)BibTeX
  ABSTRACT »

  We have measured the spectral position of the absorption minimum in a coherent population trapping resonance in thermal cesium vapor as a function of light intensity. The dependence of position on intensity is found to be almost linear. We have furthermore studied the dependence of this light shift on neon buffer gas pressure and find a strong reduction for higher pressures. So the addition of a buffer gas not only reduces the linewidth of the resonance but also a very important systematic effect for precision measurements.

1998

• B. A. Grishanin, V. N. Zadkov and D. Meschede
  Modification of resonance fluorescence and absorption in a lambda system by four-wave mixing, Phys. Rev. A 58, 4235 (1998)BibTeX
  ABSTRACT »

  A universal mechanism destroying coherence in a Λ system driven by two resonant laser fields due to four-photon interactions is analyzed theoretically. It is shown that this mechanism gives rise to novel spectral structures in resonance fluorescence. The “dark resonance” in absorption (dispersion) spectra is affected as well.

• R. Wynands, A. Nagel, S. Brandt, D. Meschede and A. Weis
  Selection rules and line strengths of Zeeman-split dark resonances, Phys. Rev. A 58, 196 (1998)BibTeX
  ABSTRACT »

  In a weak magnetic field coherent dark resonances in cesium vapor are split into up to 15 resolved components, depending on field direction and laser polarizations. We find that the selection rules are different for vapor cells with and without buffer gas due to a change in multipolarity of the two-photon coupling. At low laser intensities or sufficiently high buffer-gas pressure optical pumping between different dark resonances can be neglected so that a simple model allows one to calculate the relative line strengths, giving complete agreement with the experimental spectra.

• A. Nagel, L. Graf, A. Naumov, E. Mariotti, V. Biancalana, D. Meschede and R. Wynands
  Experimental realization of coherent dark-state magnetometers , Europhys. Lett. 44, 31 (1998)BibTeX
  ABSTRACT »

  Coherent population trapping resonances in cesium vapor can be used to determine DC flux densities in the range from 1 μT to 1 mT with typically 3·10^−5 relative uncertainty. For fields modulated at a few kHz, we find sensitivities of below 10 pT within 0.5 s integration time. From the signal-to-noise ratio the sensitivity can be extrapolated to 500 fT/√Hz. A quantitative understanding of the lineshape allows to detect DC fields of several nT even when the Zeeman components of the resonance are not resolved.

• B. A. Grishanin, V. N. Zadkov and D. Meschede
  Effect of four-photon interactions on coherent population trapping in Lambda-systems, J. Exp. Theor. Phys. 86, 79-92 (1998)BibTeX
  ABSTRACT »

  The resonance fluorescence spectrum of a Λ-system excited by two resonant light fields is calculated using a Markov analysis. Analytical formulas are derived in the strong-field limit within and beyond the rotating wave approximation. It is shown that the resonance fluorescence of the system does not vanish during coherent population trapping. Its spectrum consists of two multiplets which are similar to a triplet in the resonance fluorescence spectrum of a two-level atom and lie at the electronic transition frequencies, together with two triplets located at the frequencies of four-photon processes involving the optical excitation fields. The latter are fundamental in character and impose limits on the lower bound of the dephasing rate for the Raman resonance owing to the effect of radiative decay of the dipole transitions on the dynamics of the ground state. The effect of four-photon dephasing on the absorption spectrum of a Λ-system is analyzed and found to lead to a substantial reduction in the depth of a dip in the absorption spectrum which vanishes as the laser field strength is increased. Zh. Éksp. Teor. Fiz. 113, 144–167 (January 1998)