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Physical Review A

Theory of a two-mode phase-sensitive amplifier

Nadeem A. Ansari

Published Aug 1, 1992• 38 citations
Publisher

Abstract

A theory of two-mode phase-sensitive amplification by a three-level atomic system in the cascade configuration is presented, within the framework of the theory of multiwave mixing. Two photons of a strong external pump field induce coherence between the top and bottom levels. It is shown that both quadratures of the field modes acquire unequal gain and added noise. For large values of the dimensionless pump intensity, with a particular choice of its phase, and zero side-mode detuning, the system behaves as a nondegenerate parametric amplifier.

DOI
10.1103/physreva.46.1560

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Physical Review A•Feb 1, 1989•19 citations
A theory of two-mode phase-sensitive amplification by a three-level atomic system in the cascade configuration is presented, within the framework of the theory of multiwave mixing. Two photons of a strong external pump field induce coherence between the top and bottom levels. It is shown that both quadratures of the field modes acquire unequal gain and added noise. For large values of the dimensionless pump intensity, with a particular choice of its phase, and zero side-mode detuning, the system behaves as a nondegenerate parametric amplifier.
A linear theory of two-photon amplification by three-level atoms in the cascade configuration is developed, where a coherence is induced between the top and bottom levels, by an external classical driving field. It is shown that this system becomes an ideal parametric amplifier for sufficiently strong driving field, whereas for a weak driving field it is a phase-insensitive amplifier. In between these two extremes, one finds phase-sensitive amplification as well as squeezing for a certain range. The system does not, however, reduce to a model studied previously where the atomic coherence was treated as an initial condition. The system is also studied in a cavity configuration: It is predicted that the oscillator may behave as a two-photon correlated emission laser, i.e., its phase diffusion coefficient vanishes.
We consider a phase-sensitive amplifier that consists of a system of three-level atoms in a cascade configuration that is prepared in a coherent superposition of upper and lower states by a strong classical field. We have studied the role of pump phase fluctuations associated with the finite linewidth on the quantum-statistical properties of the radiation field. A study of the output field characteristics reveals that the presence of a very weak pump field gives rise to equal variances in both field quadratures which are independent of linewidth. On the other hand, the presence of a strong pump field alters the output field characteristics with the generation of squeezing which is later on destroyed due to the presence of phase fluctuations.
The generation and evolution of entanglement and squeezing for the two-mode fields are discussed in a cascade three-level atomic system. Two photons of a strong external pump field induce atomic coherence between the top and bottom levels. The dynamics of this system in the presence of cavity losses is studied. It is shown that entanglement and squeezing between the two modes increase initially, then decrease and eventually disappear. The periods of them are extended with the increasing of the pump field intensity. The effects of the cavity losses on squeezing and entanglement are also discussed.
We present a fully quantum-mechanical theory of nondegenerate multiwave mixing processes in three-level cascades with a two-photon pump. The explicit formulas for the resonance fluorescence spectrum and the quantum combination-tone source term are derived. The theory is applied to the generation of squeezed states of light. We find almost perfect squeezing for some strong-pump intensities and tunings within the Rabi sidebands. We find good broadband squeezing for low-pump intensities and tunings outside a small region around central tuning. Both cases avoid regions of significant spontaneous emission.