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Physical Review A

Continuous-variable entanglement and two-mode squeezing in a single-atom Raman laser

Eyob Alebachew Sete, C. H. Raymond Ooi

Published Jun 18, 2012• 11 citations
Publisher

Abstract

The quantum statistical properties of light emitted by a two-photon double Raman laser is investigated. Using the master equation derived in the good-cavity limit, we study the squeezing and entanglement properties of the cavity field. It turns out that the cavity radiation exhibits two-mode squeezing and entanglement in the transient as well as steady state regime for realizable parameters. We establish a connection between two-mode squeezing and entanglement that gives insight into the physical origin of these quantum features. We also discuss the interplay between the laser detuning and amplitude in modifying the properties of the cavity field.

DOI
10.1103/physreva.85.063819

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A steady state analysis of the nonclassical features and statistical properties of the cavity radiation of a two-photon coherent beat laser is presented. Results show that the degree of two-mode squeezing, detectable entanglement and intensity of the cavity radiation can increase with the deviation of the phase fluctuations of the laser employed in preparing the atoms, but decrease with the increasing rate at which the induced coherence superposition decays. Although it is found that varying the phase fluctuations and dephasing can lead to modification in the quantum features and statistical properties of the radiation, it does not alter the similarity in the nature of the degree of entanglement detectable by the criteria following from Duan—Giedke—Cirac—Zoller and logarithmic negativity in a perceivable manner. Since the intensity and quantum features can be readily enhanced, this system is expected to be a viable source of a strong robust entangled (squeezed) light under various conditions. Moreover, comparison of the mean number of photon pairs with intensity difference shows that the chance of inciting a two-photon process can be enhanced by changing the rate of dephasing and phase fluctuations.
We discuss the generation and evolution of entangled light in a correlated spontaneous emission laser. The master equation for the two-mode field in a cavity is derived and solved analytically. The time-dependent characteristic function in the Wigner representation for the two-mode field is obtained. It shows that the two-mode field in the cavity evolves in a two-mode Gaussian state. The entanglement degree of the two-mode field in the cavity increases initially, then decreases, and finally vanishes as the field evolves from an initial vacuum. The period of the entanglement is extended as the intensity of the driving field is increased. It is found that the entanglement still exists even when the two-mode squeezing disappears. During the entanglement period, the intensity of the field is amplified. The entanglement for the initial field being a two-mode squeezed vacuum and the entanglement of the output field are also discussed.
A steady state analysis of the nonclassical features and statistical properties of the cavity radiation of a twophoton coherent beat laser is presented.Results show that the degree of two-mode squeezing,detectable entanglement and intensity of the cavity radiation can increase with the deviation of the phase fluctuations of the laser employed in preparing the atoms,but decrease with the increasing rate at which the induced coherence superposition decays.Although it is found that varying the phase fluctuations and dephasing can lead to modification in the quantum features and statistical properties of the radiation,it does not alter the similarity in the nature of the degree of entanglement detectable by the criteria following from Duan-Giedke-Cirac-Zoller and logarithmic negativity in a perceivable manner.Since the intensity and quantum features can be readily enhanced,this system is expected to be a viable source of a strong robust entangled (squeezed) light under various conditions.Moreover,comparison of the mean number of photon pairs with intensity difference shows that the chance of inciting a two-photon process can be enhanced by changing the rate of dephasing and phase fluctuations.
We consider a nondegenerate three-level cascade laser with a subthreshold nondegenerate parametric oscillator coupled to a vacuum reservoir. Applying the pertinent master equation, we analyze the squeezing and entanglement properties of the two-mode light produced by this quantum optical system inside and outside the cavity. We also determine the normalized second-order correlation function for the two-mode light as well as for individual mode. We find that the light generated by this system is in a two-mode squeezed state and the state of the system is strongly entangled at steady state. Moreover, the presence of the parametric oscillator leads to an increase in the degree of squeezing and entanglement. We also find that the intermode correlation decreases as the injected atomic coherence decreases in the system.
Analysis of the externally induced quantum features of the cavity radiation of the two-photon correlated emission laser is presented. It turns out that the pumping process induces atomic coherence accountable for observing entanglement in the cavity radiation as well as the nonclassical photon number correlation despite the arising vacuum fluctuations. Even though a significant continuous variable entanglement is obtained near threshold in the strong driving limit, increasing the amplitude of the driving radiation more than required for a fixed value of the linear gain coefficient is found to degrade the degree of entanglement. The two-mode squeezing of the superimposed radiation, entanglement of the cavity radiation and mean number of photon pairs increase with the rate at which the atoms are injected into the cavity, but the nonclassical photon number correlation decreases. Moreover, the mean photon number corresponding to the transition from the upper energy level to the intermediate is found to be greater than the transition from the intermediate to the lower. With conceivable practical challenges, it is in principle possible to generate an intense continuous variable entanglement and quantify it via photon count measurements.