Problem of detection of Rydberg atoms and quantum information processing

We have developed a simple theoretical model describing multi-atom signals that could be measured in experiments on resonant energy transfers in an ensemble of a few Rydberg atoms. We have shown that an efficiency of the selective field-ionization detector, which is less than 1, leads to the mixing up of the spectra of the resonant energy transfer registered for various numbers of detected Rydberg atoms. This may impede the possible observations of dipole blockade or coherent two-atom interaction required to perform basic quantum gates. The formulae are presented, which help to estimate an actual mean Rydberg atom number in an excitation volume per one exciting laser pulse at a given detection efficiency. We have also found that a measurement of relationship of the amplitudes of resonances observed in the one- and two-atom signals provides a straightforward determination of the absolute detection efficiency and actual mean Rydberg atom number. This novel method is advantageous as it is independent of the specific experimental conditions. We also performed a testing experiment on the resonant energy transfers in a small excitation volume of the velocity selected Na atomic beam. The observed one- and two-atom resonances were analyzed and compared with the theoretical predictions. A good agreement between experiment and theory in the width and amplitudes of the resonances has confirmed the validity of simple approximations used in the developed theoretical model.