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Correlated quadratures of resonance fluorescence and the generalized uncertainty relation

Henk F. Arnoldus, Thomas F. George, Rolf W. F. Gross

Published May 1, 1994• 0 citations
OpenAlex

Abstract

Resonance fluorescence from a two-state atom has been predicted to exhibit quadrature squeezing below the Heisenberg uncertainty limit, provided that the optical parameters (Rabi frequency, detuning, laser linewidth, etc.) are chosen carefully. When the correlation between two quadratures of the radiation field does not vanish, however, the Heisenberg limit for quantum fluctuations might be an unrealistic lower bound. A generalized uncertainty relation, due to Schroedinger, takes into account the possible correlation between the quadrature components of the radiation, and it suggests a modified definition of squeezing. We show that the coherence between the two levels of a laser-driven atom is responsible for the correlation between the quadrature components of the emitted fluorescence, and that the Schrodinger uncertainty limit increases monotonically with the coherence. On the other hand, the fluctuations in the quadrature field diminish with an increasing coherence, and can disappear completely when the coherence reaches 1/2, provided that certain phase relations hold.

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Resonance fluorescence from a two-state atom has been predicted to exhibit quadrature squeezing below the Heisenberg uncertainty limit, provided that the optical parameters (Rabi frequency, detuning, laser linewidth, etc.) are chosen carefully. When the correlation between two quadratures of the radiation field does not vanish, however, the Heisenberg limit for quantum fluctuations might be an unrealistic lower bound. A generalized uncertainty relation, due to Schroedinger, takes into account the possible correlation between the quadrature components of the radiation, and it suggests a modified definition of squeezing. We show that the coherence between the two levels of a laser-driven atom is responsible for the correlation between the quadrature components of the emitted fluorescence, and that the Schrodinger uncertainty limit increases monotonically with the coherence. On the other hand, the fluctuations in the quadrature field diminish with an increasing coherence, and can disappear completely when the coherence reaches 1/2, provided that certain phase relations hold.
The quadrature squeezing spectra produced in the resonance fluorescence of a two-level atom driven by a strong coherent field and a weak amplitude-fluctuating field are investigated. For far-off-resonance and strong excitation, the resonance fluorescence exhibits two-mode squeezing around the Rabi sideband frequencies. Thus we have a source of two mode squeezing that is very easily frequency tuned simply by adjusting the generalized Rabi frequency. The presence of the strength of the stochastic process reduces the degree of squeezing obtainable. The quadrature squeezing spectra are also effected by the relative phase of the two fields.
The quadrature squeezing spectra produced in the resonance fluorescence of a two-level atom are investigated, including the effects of a finite laser bandwidth due to phase diffusion. For resonant excitation at low intensities, the fluorescence field exhibits narrow bandwidth squeezing in the out-of-phase quadrature, centered at the laser frequency. Otherwise, squeezing occurs only in the in-phase quadrature. Specifically, for slightly off-resonance and weak excitation, the squeezing still centers at the laser frequency, with a finite bandwidth of the order of $\ensuremath{\gamma}.$ More importantly, for far-off-resonance and strong excitation, the resonance fluorescence exhibits two-mode squeezing around the Rabi sideband frequencies. Thus we have a source of two-mode squeezing that is very easily frequency tuned simply by adjusting the generalized Rabi frequency. The presence of a laser linewidth substantially reduces the degree of squeezing obtainable. The fluorescence shows no squeezing at all when the laser linewidth is greater than the atomic spontaneous emission linewidth.
We investigate steady-state squeezing in the phase quadratures of the resonance fluorescence emitted from a three-level V-type atom driven by two coherent fields and damping in common vacuum. Quantum fluctuation spectra of the optimum-phase quadratures are calculated. We find that the steady-state squeezing of the observed driven transition between the excited state and the ground state is strongly affected by the decay rate of the controlling transition, detuning and intensity of driven fields, and the phase quadrature of fluorescent light. When the decay rate of the controlling transition approaches zero, and the driving fields are not resonant simultaneously, the squeezing peak can be extra narrow and the squeezing can be deeply enhanced to exceed the degree of squeezing for the driven two-level atom. We provide numerical results in support of our arguments for arbitrary values of the atomic and field parameters and also develop an analytic description in the limit of strong driving fields that leads to explicit lineshape and linewidth formulae.
Abstract The squeezing spectrum of the fluorescence field emitted from a four-level atom in J = 1/2 to J = 1/2 configuration driven by two coherent fields is studied. We find that the squeezing properties of the fluorescence radiation are significantly influenced by the presence of vacuum-induced coherence in the atomic system. It is shown that such coherence induces spectral squeezing in phase quadratures of the fluorescence light for both weak and strong driving fields. The dependence of the squeezing spectrum on the relative phase of the driving fields is also investigated. Effects such as enhancement or suppression of the squeezing peaks are shown in the spectrum as the relative phase is varied. An analytical explanation of the numerical findings is presented using dressed-states of the atom-field system.
The spectrum of quantum fluctuations in phase quadratures of resonance fluorescence of a three-level V-type atom driven by a coherent field is investigated. We find that quantum interference between two decay channels of the atom can greatly modify the spectrum. We show that for weak excitation, quantum interference can greatly enhance squeezing and change the phase quadrature in which the maximum squeezing occurs. We also show that for strong and far-off-resonance excitation two deeply squeezing peaks appear at the Rabi sideband frequencies and quantum interference broadens the squeezing peaks.
We investigate steady-state squeezing in the phase quadratures of the resonance fluorescence emitted from a coherently driven four-level atom of $\ensuremath{\Lambda}$ configuration. Quantum fluctuation spectra of the optimum-phase quadratures are calculated. We show that if quantum interference between spontaneous emission channels from closed excited states to lower levels of the atom takes place, squeezing in the optimum-phase quadrature can occur in a very wider region of the parameter space than that predicted by previous studies. We also show that the quantum interference can greatly change the atomic coherences and then lead to this interesting result.