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Chinese Physics Letters

Squeezed Quantum-Beat Laser Without Inversion

Xiangming Hu, Jin-sheng Peng

Published Dec 1, 1998• 3 citations
Publisher

Abstract

A quantum-beat laser without inversion is proposed for producing two-mode suqeezing. Using the dressed-atom-dressed-mode approach, the master equation is derived and the variances in the sum mode intensity and in the relative amplitude and phase are calculated. When the laser is operated well above threshold, the intensity fluctuations in the sum mode are reduced below the shot noise limit with an optimum Mandel parameter of -0.5. At the same time, the fluctuations in the relative amplitude and phase are retained at their vaccum noise levels.

DOI
10.1088/0256-307x/15/12/008

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Physical Review A•Oct 8, 2008•35 citations
A quantum-beat laser without inversion is proposed for producing two-mode suqeezing. Using the dressed-atom-dressed-mode approach, the master equation is derived and the variances in the sum mode intensity and in the relative amplitude and phase are calculated. When the laser is operated well above threshold, the intensity fluctuations in the sum mode are reduced below the shot noise limit with an optimum Mandel parameter of -0.5. At the same time, the fluctuations in the relative amplitude and phase are retained at their vaccum noise levels.
Using the `dressed-atom-dressed-mode' approach and separating the decoupled atomic state, we investigate the statistical properties of a quantum-beat laser without inversion. While the fluctuations of the relative amplitude and phase are retained at their vacuum noise levels, the intensity fluctuations in the sum mode are reduced below the shot noise limit with an optimum Mandel parameter when the laser is operated well above threshold. In particular, we show that the decoupled atomic state significantly relaxes the parameter requirement for squeezing. The physical cause is also explained.
It is shown that the Λ quantum beat system, into which a new atomic coherence is introduced, can produce bright two-mode sub-Poissonian light. The Mandel Q parameter is calculated using Scully-Lamb theory. On one hand, when quantum noises of the relative amplitude and relative phase drop to vaccum noise levels, the average mode exhibits sub-Poissonian photon distribution; when quantum noises of the average amplitude and average phase drop to vaccum noise levels, the relative mode exhibits sub-Poissonian photon statistics; the optimum Mandel Q parameter is -0.5. On the other hand, in the above two cases, each of the correlated spontaneous emission laser modes exhibits sub-Poissonian photon statistics with optimum Mandel Q parameter of -0.25.
We present the quantum theory of a two-mode Lambda-type three level quantum-beat laser with injected atomic coherences. The lower two levels are coupled by an external classical field. The master equation and the Fokker–Planck equation are derived. Phases of the two modes are locked to a value depending on the phase of the external field, the phase of the injected coherence and the population of the lower two levels. Lasing without inversion and without threshold is found for both modes with and without injected coherences. Applying the appropriate initial atomic coherences one can switch intensities between the two modes, as well as bifurcation and multiple branching can be found when coherences among all levels are present. It is also possible to find phase bistability at a fixed intensity for one of the two modes, when high pump is applied. Strong intensity and phase noise reduction can be found in one of the modes at the expense of increased noises in the other one. Near Poissonian noise can be achieved. This research was supported by a grant of the Office of Naval Research.
In this paper we investigate the quantum statistical properties in a cascade laser system with the lower transition being in a quantum-beat configuration. It is shown that a type of three-mode squeezing may be generated. The fluctuations of the intensity difference between the sum-mode from the quantum-beat and the cascade single mode may be reduced below the shot-noise limit. The best achievable noise reduction is up to 50%. Good squeezing occurs when the sum mode and the cascade single mode have normalized intensities much larger than unity and the intensity difference is much smaller than the respective intensity.
We show that a quantum-beat system with incoherent pump or coherent driving produces an entangled sub-shot-noise laser that operates well above threshold. The numerical results and physical analyses are presented using the combination modes of the lasing fields. The relative mode is decoupled from the active medium and thus remains in its vacuum state, while the sum mode operates well above threshold and has sub-shot-noise. The quantum beat and the sum mode intensity noise reduction combine to yield entanglement between two bright beams and sub-Poissonian photon statistics of the respective beams.