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Physical Review A

Intensity-intensity correlations and quantum interference in a driven three-level atom

S. Swain, Peng Zhou, Z. Ficek

Published Mar 15, 2000• 53 citations
Publisher

Abstract

We investigate the two-time intensity correlation functions of the fluorescence field emitted from a $V$-type three-level atom. We are particularly interested in the manner in which the atom emits photons in the presence of quantum interference. We show that under strong-field excitation quantum interference leads to anticorrelations of photons emitted from the atomic excited levels which can exist for extremely long times. This indicates that the excited atomic levels are not the preferred radiative states. We find that the atom spends most of its time in a superposition of the excited atomic levels from which it emits strongly correlated photons. The strong correlations are present only for a nonzero splitting between the excited levels, and for degenerate levels the correlations reduce to that of a two-level atom. Moreover, we find that the transition from the ground level to the symmetric superposition of the excited levels does not saturate even for a strong driving field. We also calculate the correlation functions for a weak driving field, and find that in this case the photon correlations are not significantly affected by quantum interference, but the atom can emit a strongly correlated pair of photons produced by a three-wave mixing process. Under appropriate conditions, with near-maximal quantum interference, it is possible to make the maximum value of the correlation function extremely large, in marked contrast with the corresponding case with no quantum interference.

DOI
10.1103/physreva.61.043410

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The joint probability P 12 of detecting two photons at two different positions in the interference of a classical field with the resonance fluorescence field from a coherently driven two-level atom is investigated. We find that P 12 shows a stronger modulation with detector separation than is predicted by a classical wave theory. Under stationary conditions and if the driving field is strong enough to saturate the atomic transition, the relative modulation amplitude a of the P 12 pattern reaches its maximum possible value a = 1 for E → 0 (where E is the classical field amplitude), but simultaneously the whole phenomena vanishes, P 12 → 0. For equal intensities of the classical and the resonance fluorescent field we have a = ⅔. Compared with this, a classical wave theory predicts a possible maximum value of a = ½.
In this paper, we investigate the spontaneously generated coherence (SGC) effects on the fluorescence fields intensity-intensity correlation in a resonant driven four-level Y-type atomic system. By using a strong control field, in the absense of SGC effects, strong correlation and anticorrelation fluorescence photons can be produced from two ladder transitions in this system respectively. However, in the presence of SGC effects, the fluorescence fields correlation properties are reversed for the two transitions. The above phenomena can be traced to the quantum destructive or constructive interference in terms of dressed states.
We study the intensity–intensity correlation in a closely spaced doublet V-type three-level atom driven by an external coherent field and damped by a broadband squeezed vacuum. We are interested in the manner in which the atom emits photons under the combined effect of quantum interference and squeezed vacuum. For distinguishable photons and degenerate transitions, the squeezed field produces anticorrelation, whereas for nondegenerate transitions the effect of the squeezed field is the surpassing of the antibunching during certain time intervals. We find that bunching/antibunching behaviour and the symmetry of the two emission processes can be controlled by the relative phase of the squeezed vacuum to the coherent field. For particular conditions we show a bunching behaviour which turns to antibunching when the two-photon correlations in the squeezed vacuum are reduced to the classical level. Therefore, this transition must be attributed to the quantum nature of the squeezed vacuum. We also study the sideband correlations. We find that squeezed vacuum makes the sidebands evolve at different rates which are phase dependent.