Paulo Valente

Noise spectroscopy of nonlinear magneto-optical resonances in Rb vapor

Nonlinear magneto-optical resonances occurring for near-zero magnetic field are studied in Rb vapor using light-noise spectroscopy. With a balanced detection polarimeter, we observe high contrast variations of the noise power (at fixed analysis frequency) carried by diode laser light resonant with the 5S{sub 1/2} (F=2){yields}5P{sub 1/2} (F=1) transition {sup 87}Rb and transmitted through a rubidium vapor cell as a function of magnetic field B. A symmetric resonance doublet of anticorrelated noise is observed for orthogonal polarizations around B=0 as a manifestation of ground-state coherence. We also observe sideband noise resonances when the magnetic field produces an atomic Larmor precession at a frequency corresponding to one-half of the analysis frequency. The resonances on the light fluctuations are the consequence of phase to amplitude noise conversion owing to nonlinear coherence effects in the response of the atomic medium to the fluctuating field. A theoretical model (derived from linearized Bloch equations) is presented that reproduces the main qualitative features of the experimental signals under simple assumptions.

Polarization squeezing of light by single passage through an atomic vapor

We have studied relative-intensity fluctuations for a variable set of orthogonal elliptic polarization components of a linearly polarized laser beam traversing a resonant

Experimental observation of three-color optical quantum correlations

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Temporal buildup of electromagnetically induced transparency and absorption resonances in degenerate two-level transitions

Rb vapor cell. Significant polarization squeezing at the threshold level (-3dB) required for the implementation of several continuous variables quantum protocols was observed. The extreme simplicity of the setup, based on standard polarization components, makes it particularly convenient for quantum information applications.

Numerical investigation of the quantum fluctuations of optical fields transmitted through an atomic medium

Quantum correlations among bright pump, signal, and idler beams produced by an optical parametric oscillator, all with different frequencies, are experimentally demonstrated. We show that the degree of entanglement between signal and idler fields is improved by using information on pump fluctuations. To our knowledge this is the first observation of three-color optical quantum correlations.

Vectorial atomic magnetometer based on coherent transients of laser absorption in Rb vapor

The temporal evolution of electromagnetically induced transparency (EIT) and absorption (EIA) coherence resonances in pump-probe spectroscopy of degenerate two-level atomic transition is studied for light intensities below saturation. Analytical expressions for the transient absorption spectra are given for simple model systems and a model for the calculation of the time-dependent response of realistic atomic transitions, where the Zeeman degeneracy is fully accounted for, is presented. EIT and EIA resonances have a similar (opposite sign) time-dependent line shape, however, the EIA evolution is slower and thus narrower lines are observed for long interaction time. Qualitative agreement with the theoretical predictions is obtained for the transient probe absorption on the {sup 85}Rb D{sub 2} line in an atomic beam experiment.

A chemical analysis of sediment pore water in oxygen-free atmosphere: application to a contaminated area

We have numerically solved the Heisenberg-Langevin equations describing the propagation of quantized fields through an optically thick sample of atoms. Two orthogonal polarization components are considered for the field and the complete Zeeman sublevel structure of the atomic transition is taken into account. Quantum fluctuations of atomic operators are included through appropriate Langevin forces. We have considered an incident field in a linearly polarized coherent state (driving field) and vacuum in the perpendicular polarization and calculated the noise spectra of the amplitude and phase quadratures of the output field for two orthogonal polarizations. We analyze different configurations depending on the total angular momentum of the ground and excited atomic states. We examine the generation of squeezing for the driving field polarization component and vacuum squeezing of the orthogonal polarization. Entanglement of orthogonally polarized modes is predicted. Noise spectral features specific of (Zeeman) multi-level configurations are identified.

Squeezing and entanglement of optical fields transmitted through a thick atomic medium

We have designed and tested an atomic vectorial magnetometer based on the analysis of the coherent oscillatory transients in the transmission of resonant laser light through a Rb vapor cell. We show that the oscillation amplitudes at the Larmor frequency and its first harmonic are related through a simple formula to the angles determining the orientation of the magnetic field vector. The magnetometer was successfully applied to the measurement of the ambient magnetic field.

Experimental three-color optical quantum correlations

. 1990; van Raaphorst & Malschaert, 1996). However, sediment pore water sampling is tedious and requires the use of special equipment due to the possible effects and potential chemical alterations resulting from incorrect procedures. It is known that, with the exception of the uppermost sediment layers (of 1 to 3 cm thickness), most fine-grained deposits are anoxic but oxidize rapidly upon exposure to air. The oxidation of the sediments brings about rapid changes in the kinds of redox-sensitive chemicals dissolved in the sediment pore water. During pore water collection and sample processing the maintenance of an oxygen-free atmosphere is essential for the measurement of some of the original chemical constituents (Manheim, 1976; Kriukov & Manheim, 1982). Results from many studies indicate that nutrient concentrations of pore water may be much higher than those of the water column (Ohle, 1977; Esteves, 1988; van Raaphorst & Malschaert, 1996). Generally, glove bags or glove boxes should be used to handle the pore water samples that best represent the natural sedimentary environment. It is essential, to ensure these conditions, that any exposure of the sediment and sampled water to the atmosphere must be completely avoided by guaranteeing oxygen-free conditions during the entire process of sediment sample manipulation (Adams, 1991). This can be achieved by working in the inert atmosphere of such a gas as nitrogen, argon or, in some cases, helium or carbon dioxide. __________

Laser-noise-induced correlations in electromagnetically induced transparency

Propagation of a quantized optical field through a thick sample of two-level atoms, considering the complete Zeeman sublevel structure, is theoretically investigated. Squeezing and entanglement between orthogonal polarization components is predicted for the transmitted field.