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arXiv:1912.05420 · Journal of Physics B Atomic Molecular and Optical Physics

Squeezing in resonance fluorescence via vacuum induced coherences

H. B. Crispin, R Arun

Published Nov 27, 2019• 6 citations
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Abstract

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.

DOI
10.1088/1361-6455/ab5c3a

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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.
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.
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.
The quadrature squeezing spectra in the resonance fluorescence of a V-type three-level atom driven by a coherent field and coupled to a single-mode cavity is investigated. For weak excitation, the fluorescence field exhibit squeezing in the out-of-phase quadrature. The coupling between the atom and the cavity mode can greatly enhance the squeezing centred at the laser frequency. More importantly, for strong excitation, under the effect of the cavity-atom coupling, the in-phase quadrature of fluorescence can exhibit two-mode squeezing at the two inner sideband frequencies. By working in the dressed-state representation and hiring secular approximation, we give an analytical explanation for the effect. The result shows, under appropriate conditions, the squeezing can be greatly enhanced by appropriately tuning the cavity resonant frequency.
We study squeezing properties of the fluorescence radiation emitted by a driven ΛΛΛ-type atom in which the metastable lower energy levels are coupled by an additional field. We find that the relative phase of the applied fields can significantly modify the squeezing characteristics of radiation. It is shown that the additional field connecting the lower levels in the system can induce spectral squeezing in a parameter regime for which the squeezing is absent without the additional field. Moreover, the squeezing can be shifted from inner- to outer-sidebands of the spectrum by simply changing the relative phase. A dressed-state description is presented to explain these numerical results. The phase control of squeezing in the total variance of quadrature components is also examined. We show that the squeezing in total variance attains its maximal value when the system reduces to an effective two-level system.
We investigate the effects of spontaneously generated interference on the spectrum of quantum fluctuations in phase quadratures of resonant fluorescence emitted from the transition of j = 1/2 to j = 1/2 of a monochromatically driven four-level atom with antiparallel dipole moments. It is found that the spectrum exhibits obvious characteristics of quantum interference in both cases of weak and strong laser fields. For the Zeeman-degenerate system, strong radiation squeezing in weak atomic excitation can occur at the central frequency of the spectrum, which is quite different from the case without consideration of the interference. Moreover, when we apply an external magnetic field to the atom, we find that the quantum interference can lead to a narrowing spectrum with much stronger squeezing by adjusting the magnetic field strength. These results suggest that the phase-dependent fluorescence spectrum can serve as a probe of the quantum interference effects in a realistic system such as a trapped 198Hg+ ion or charged quantum dots.
We present an experimental realization of resonance fluorescence in squeezed vacuum.We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier.We investigate the fluorescence spectra in the weak and strong driving regimes, observing up to 3.1 dB of reduction of the fluorescence linewidth below the ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum on the relative phase of the driving and squeezed vacuum fields.Our results are in excellent agreement with predictions for spectra produced by a two-level atom in squeezed vacuum [Phys.Rev. Lett.58, 2539 (1987)], demonstrating that resonance fluorescence offers a resource-efficient means to characterize squeezing in cryogenic environments.