Recent Experiments with the Micromaser

  • H. Walther
Conference paper


The one-atom maser or micromaser allows one to study the resonant interaction of a single atom with a single mode of a superconducting niobium cavity.1–4 In previous experiments values of the quality factor as high as 3 × 1010 have been achieved for the resonant mode, corresponding to an average lifetime of a photon in the cavity of 0.2 s. The photon lifetime is thus much longer than the interaction time of an atom with the maser field. The atoms used in the experiments are rubidium Rydberg atoms pumped by laser excitation into the upper level of the maser transition, which is usually induced between neighboring Rydberg states. In the experiments the atom-field interaction is probed by observing the population in the upper and lower maser levels after the atoms have left the cavity. The field in the cavity consists only of single or a few photons. Nevertheless, it is possible to study the interaction in considerable detail. The dynamics of the atom-field interaction treated with the Jaynes-Cummings model was investigated by selecting and varying the velocity of the pump atoms.2 The counting statistics of the pump atoms emerging from the cavity allowed us to measure the non-classical character of the cavity field3,4 predicted by the micromaser theory. It also has been observed that under suitable experimental conditions the maser field exhibits metastability and hysteresis.5 Most of the maser experiments so far have been performed at cavity temperatures of 0.5 K. Recently, a further reduction of the temperature to below 0.1 K was achieved by using an improved setup in a dilution refrigerator.5


Photon Number Maser Field Exit Hole Static Electric Field Cavity Frequency 
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Copyright information

© Springer Science+Business Media New York 1996

Authors and Affiliations

  • H. Walther
    • 1
  1. 1.Sektion Physik der Universität MünchenMax-Planck-Institut für QuantenoptikGarchingFed. Rep. of Germany

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