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Physical Review Letters

Realization of a two-photon maser oscillator

M. Brune, J. M. Raimond, P. Goy, L. Davidovich, S. Haroche

Published Oct 26, 1987• 564 citations
Publisher

Abstract

We have built the first quantum oscillator working on two-photon stimulated emission of radiation. It oscillates continuously on a degenerate two-photon transition between the levels 40S and 39S of rubidium atoms. The oscillation is sustained in a Q\ensuremath{\simeq}${10}^{8}$ niobium superconducting cavity at 68.415 87 GHz. At threshold, this new maser system operates with only a few atoms and a few tens of photons at a time in the cavity.

DOI
10.1103/physrevlett.59.1899

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We have built the first quantum oscillator working on two-photon stimulated emission of radiation. It oscillates continuously on a degenerate two-photon transition between the levels 40S and 39S of rubidium atoms. The oscillation is sustained in a Q\ensuremath{\simeq}108{10}^{8}108 niobium superconducting cavity at 68.415 87 GHz. At threshold, this new maser system operates with only a few atoms and a few tens of photons at a time in the cavity.
A Rydberg atom maser operated on a two-photon degenerate atomic transition is discussed. This device combines two interesting features: it is a quantum oscillator working on an intrinsically nonlinear effect and it is a micromaser, with only a few atoms and a few tens of photons at a time in the cavity. The reasons why Rydberg atom-superconducting cavity systems are well adapted for two-photon maser studies are discussed, and the main properties of the device are analyzed by comparing it to Rydberg masers operating on one-photon transitions.>
We present the quantum theory of a microscopic maser operating on a degenerate two-photon transition between levels of the same parity. We derive both a master equation and a Fokker-Planck equation for this system, and show that quantum effects may have a substantial influence on the behavior of the maser. They modify the oscillation threshold and make external triggering of this maser unnecessary, whereas, according to semiclassical theory, such a triggering is required to start up the maser oscillation. We derive the phase-diffusion properties of the field and show that the diffusion coefficient is complex in this case, its imaginary part being associated with a frequency shift of the field inside the cavity. We show that, in steady state, the photon-number statistics is sub-Poissonian for a wide range of pumping rates.
The one-atom maser or micromaser is, in contrary to ordinary masers and lasers, a pure quantum device operating with only a few photons and less than one pump atom on the average in the maser cavity. It is thus an ideal device to study quantum phenomena such as the generation of nonclassical light. The cavity is a superconducting niobium microwave resonator with a high quality factor (up to 3 × 1010). Using a single trapped ion related experiments can now also be performed in the infrared spectral region.
The work on the one-atom maser is reviewed. The superconducting maser cavity made of niobium and cooled to 0.5 K to exclude thermal photons has a quality factor of 3 X 1010. Velocity-selected Rydberg atoms pump the maser. The field inside the cavity is investigated by probing the atoms leaving the cavity. The dynamics of the Rabi nutation were investigated. Furthermore, the statistics of the photons in the cavity were determined to be sub-Poissonian corresponding to photon-number fluctuations of 70% below the vacuum-state limit. The one-atom maser is the only maser system which leads to nonclassical radiation even when pumping processes with Poissonian statistics are used. Some applications of the one- atom maser to study the quantum measurement process also are discussed.
. 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.