Fluorescence control through vacuum induced coherences

Abstract

The resonance fluorescence of a four-level atom in J = 1/2 to J = 1/2 transition driven by two coherent fields is studied. We find that the incoherent fluorescence spectrum shows a direct indication of vacuum-induced coherence in the atomic system. We show that such coherence manifests itself via an enhancement or suppression of the spectral peaks in the π-polarized fluorescence. The effect of the relative phase of the driving fields on the spectral features is also investigated. We show that phase-dependent enhancement or suppression of the fluorescence peaks appears in the incoherent spectrum emitted along the σ transitions. It is found that this phase dependence occurs because of the polarization-detection scheme employed for the observation of the fluorescence light. We present an analytical explanation, based on dressed-states of the atom-field system, to interpret the numerical results. 1 2 4 3 γ 1 γ σ γ σ m j = -1 / 2 m j = +1 / 2 γ 2 Δ Ω  Ω  Ω b y Atom ( E b , ϕ b ) (E  , ϕ  ) Laser Laser Detector Polarizer z x FIG. 1: (a) The level scheme of a four-level atom with J = 1/2 to J = 1/2 transitions driven by coherent fields. The transitions |1 ↔ |3 and |2 ↔ |4 are driven by a linearly polarized field while a σ − -polarized field induces the transitions |1 ↔ |4 in the atom. (b) The arrangement for laser fields driving the atom and the detection of the fluorescence spectrum.

Squeezing in resonance fluorescence via vacuum induced coherences

“…Thus, one finds that the relative phase (φ) can not only suppress squeezing as shown in previous studies [23] but also cause enhancement of squeezing in the spectrum at the same time. This result is closely similar to that in the incoherent spectrum of resonance fluorescence reported in our previous work [29].…”

“…With the inclusion of spontaneous decay terms, the time evolution of the density matrix elements can be obtained using equation (3) to be [29]…”

“…In the present system, the phase control of spectral features appears because of the polarization-dependent detection schemed used to observe the fluorescence light as shown in figure 1(b). Note that the phase dependence occurs because only the e x -component of the fluorescence field is detected along the σ transitions [29]. To demonstrate the role of the relative phase, we plot in figure 6 the in-phase quadrature spectrum for strong off-resonance excitation.…”

“…In these studies [25][26][27][28], the fluorescence properties are investigated when the π transitions in the atom are driven by a linearly polarized light. Recently, we have shown that the effect of VIC in the fluorescence spectrum becomes stronger when an additional σ − -polarized light drives the atom with J = 1/2 to J = 1/2 transition [29]. It has been shown that the incoherent spectrum of fluorescence emitted on the σ transitions is dependent on the relative phase of the applied fields.…”

Quantum interference in the resonance fluorescence of a $J=1/2 - J'=1/2$ atomic system: Quantum beats, nonclassicality, and non-Gaussianity

“…Particular attention has been devoted to the spectrum [3][4][5][6], time-energy complementarity [4,5], Young's interference [7], photon correlations [8], frequency-resolved photon correlations [9], squeezing [10], phase shifts [11], and cooperative effects in photon correlations [12]. The case of additional laser excitation of one of the σ transitions on the spectrum and squeezing has been studied in [13][14][15].…”