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The single atom laser: a quantized Rabi oscillator

Kyungwon An, Changhuei Yang, Ramachandra Rao Dasari, Michael S. Feld

Published Jun 7, 1996• 0 citations
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Abstract

Summary form only given. We have recently developed the first working single-atom microlaser in which coherent light is generated by means of the interaction of a single two-level atom with a single mode of the radiation field. The photon generation process follows the Jaynes-Cummings model, and photon buildup is initiated by vacuum Rabi oscillations, not by spontaneous emission as in conventional lasers. We measured the mean photon number in the cavity (n) as a function of the average number of atoms present there . Laser oscillation was observed with as small as 0.1, resulting in (n) of 0.1.

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Quantum Optics Journal of the European Optical Society Part B•Apr 1, 1990•29 citations
Summary form only given. We have recently developed the first working single-atom microlaser in which coherent light is generated by means of the interaction of a single two-level atom with a single mode of the radiation field. The photon generation process follows the Jaynes-Cummings model, and photon buildup is initiated by vacuum Rabi oscillations, not by spontaneous emission as in conventional lasers. We measured the mean photon number in the cavity (n) as a function of the average number of atoms present there . Laser oscillation was observed with as small as 0.1, resulting in (n) of 0.1.
We have achieved the first realization of a single atom microlaser, a laser oscillator with only one atom in an optical resonator. In the experiment a beam of two-level barium atoms traverses an ultrahigh Q single-mode cavity. The atoms are inverted by a (pi) -pulse field before they enter the cavity. Laser oscillation ((lambda) equals 791 nm) has been observed, with the mean number of atoms inside the mode <N> as small as 0.1, resulting in the mean number of photons in the mode <N> or 0.14. To understand the results quantitatively we used a fully-quantized one-atom microlaser theory adapted from its counterpart micromaser theory. The present theory was found to be in good agreement with the data for small <N> and <n>. Discrepancy between experiment and theory was observed for <n> very much greater than 1 and <N> approximately equal to 1. This discrepancy may be explained by the standing-wave nature of the cavity mode, in combination with the saturation effect occurring at large cavity photon number, as well as by the breakdown of single-atom interaction assumption in the theory for <N> greater than or equal to 1.
The single-atom microlaser is one and the only type of single atom lasers realized experimentally so far. The gain medium is a beam of excited, non-interacting two-level atoms (/spl lambda/=791 nm, /sup 3/P/sup 1//spl rarr//sup 1/S/sub 0/ transition of /sup 138/Ba) entering an ultra-low loss resonator one at a time. This laser device utilizes the coherent atom-cavity interaction, often referred to as quantized Rabi oscillation, as the light amplification method, With the mean atom number about unity, tens of photons could be stored inside the cavity. The laser oscillation persisted with the mean number of atoms in the cavity well below unity.
We have studied the statistical and squeezing properties of the cavity light generated by a two-level laser. This optical system contains N two-level atoms available in a cavity coupled to a single-mode vacuum reservoir. They are pumped to the top level from the bottom level by means of the electron bombardment. Applying the steady-state solutions of the equations of evolution of the expectation values of the atomic operators and the quantum Langevin equation, we obtained the global and local photon statistics of the single-mode light beam. We have found that, for the two-level laser operating well above the threshold, the uncertainties in the plus and minus quadratures are equal and satisfy the minimum uncertainty relation. In view of this, we have identified the light generated by the laser operating well above threshold to be coherent. On the other hand, the light generated by the laser operating at threshold is found to be chaotic. From the obtained results, we have also observed that a large part of the local mean photon number, the local photon number variance, and the local quadrature variance are confined in a relatively narrow frequency interval.
. In this paper experiments performed with the one-atom maser are reviewed. Furthermore, possible experiments to test basic quantum physics are discussed. Introduction, the One-Atom-Maser The most promising avenue to study the generation process of radiation in lasers and masers is to drive a maser consisting of a single mode cavity by single atoms. This system, at first glance, seems to be another example of a Gedanken-experiment treated in the pioneering work of Jaynes and Cummings (1963), but such a one-atom maser (Meschede, Walther and Müller, 1985) really exists and can in addition be used to study the basic principles of radiation-atom interaction. The advantages of the system are: it is the first maser which sustains oscillations with less than one atom on the average in the cavity, this setup allows to study in detail the conditions necessary to obtain nonclassical radiation, especially radiation with sub-Poissonian photon statistics in a maser system directly in a Poissonian pumping process, and it is possible to study a variety of phenomena of a quantum field including the quantum measurement process. What are the tools that make this device work: It was the enormous progress in constructing superconducting cavities together with the laser preparation of highly excited atoms – Rydberg atoms – that have made the realization of such a one-atom maser possible.
The authors have investigated the spectrum of the emitted light by a single atom interacting with a single mode of the radiation in an ideal cavity via the intensity-dependent coupling (the Jaynes-Cummings model with intensity-dependent coupling see B. Buck, Phys. Lett., vol.A81, p.132 (1981)). From the authors' results it follows that in the resonant case the two-peaked structure of the spectrum associated with the vacuum-field Rabi splitting is preserved for any initial state of the radiation field (e.g. number state, thermal state, coherent state and the squeezed vacuum) with an arbitrary average number of photons.