Trichromatic phase manipulation of the response of a two-level medium to an arbitrarily intense probe field

The phase dependence and independence of the response of a trichromatically driven two-level medium to an arbitrarily intense probe field have been studied. The sum of the relative phases of the sideband components of the trichromatic field compared to the central component plays a crucial role in the response of the medium. For a weak probe field, as the sum of the relative phases changes from The phase dependence and independence of the response of a trichromatieally driven two-level medium to an arbitrarily intense probe field have been studied. The sum of the relative phases of the sideband components of the trichromatic field compared to the central component plays a crucial role in the response of the medium. For a weak probe field, as the sum of the relative phases changes from 0 to π, multiple switching can be achieved, in which switching from normal to anomalous dispersion occurs in multiple separate frequency regimes. The remarkable dependence on the sum phase is also shown for a strong probe field. On the other hand, when the sum of the two relative phases is fixed, the changes in the respective phases have no influence on the response of the medium.     

Phase Dependence of Fluorescence Spectrum of a Two-Level Atom in a Trichromatic Field

We examine the phase-dependent effects in resonance fluorescence of a two-level atom driven by a trichromatic modulated field. It is shown that the fluorescence spectrum depends crucially on the sum of relative phases of the sideband components compared to the central component, not simply on the respective phases. The appearance or disappearance of the central peak and the selective elimination of the sideband peaks are achieved simply by varying the sum phase. Once the sum phase is fixed, the spectrum keeps its features unchanged regardless of the respective relative phases.     

Control of Spinning Sidebands in High Resolution NMR Spectroscopy

The presence of spinning sidebands can severely compromise the detection of low molarity analytes. Spinning sidebands have traditionally been minimized by improving the magnetic field homogeneity and by varying the spinning of the sample in a linear fashion during data acquisition. The effect of the latter is to spread the spinning sideband intensity over a range of frequencies so that the final result is a spinning sideband whose shape reflects the distribution of spinning speeds. We have designed a customized profile of spinner speed variation that optimizes the reduction of spinning sidebands. The customized profile is based on theoretical considerations of how the intensity of sidebands vary with the rate of sample rotation and also compensates for the mechanical design of the spinner mechanism. The result is a unique combination of an exponential increase in gas flow rate to balance the theoretical considerations coupled with a strategically placed rapid change in air flow to annul the sluggish response of the spinning mechanism to acceleration. The resulting sideband shape is a broad, flat, square step in the baseline that is least likely to interfere with low molarity analyte peaks.     

Intensity dependence of laser-assisted attosecond photoionization spectra

We study experimentally the influence of the intensity of the infrared (IR) probe field on attosecond pulse train (APT) phase measurements performed with the RABITT method (Reconstruction of Attosecond Beating by Interference in Two-Photon Transitions). We find that if a strong IR field is applied, the attosecond pulses will appear to have lower-than-actual chirp rates. We also observe the onset of the streaking regime in the breakdown of the weak-field RABITT conditions. We perform a Fourier-analysis of harmonic and sideband continuum states and show that the mutual phase relation of the harmonics can be extracted from higher Fourier components.     

Sub-half-wavelength localization of a two-level atom via trichromatic phase manipulation

We show that it is possible to localize a two-level atom in a half-wavelength region by using a trichromatic field to drive the atom. Of the trichromatic components, one sideband is a standing-wave field with position-dependent amplitude. By varying the sum of relative phases of the sidebands of the trichromatic field to the central component, the atom is localized in either of the two half-wavelength regions with 50% detecting probability when the spontaneously emitted photons are detected.     

Tunable second-order sideband effects in hybrid optomechanical cavity assisted with a Bose—Einstein condensate

We theoretically investigated a second-order optomechanical-induced transparency (OMIT) process of a hybrid optomechanical system (COMS), which a Bose—Einstein condensate (BEC) in the presence of atom—atom interaction trapped inside a cavity with a moving end mirror. The advantage of this hybrid COMS over a bare COMS is that the frequency of the second mode is controlled by the s-wave scattering interaction. Based on the traditional linearization approximation, we derive analytical solutions for the output transmission intensity of the probe field and the dimensionless amplitude of the second-order sideband (SS). The numerical results show that the transmission intensity of the probe field and the dimensionless amplitude of the SS can be controlled by the s-wave scattering frequency. Furthermore, the control field intensities, the effective detuning, the effective coupling strength of the cavity field with the Bogoliubov mode are used to control the transmission intensity of the probe field and the dimensionless amplitude of the SS.     

Dynamic Quantum Erasure Mediated by Electromagnetically Induced Transparency

We propose a scheme on control of the transition from quantum decoherence to coherence of a considered system S provided by the polarization degree of freedom of a probe field coupled to its motional degrees of freedom representing the environment B. A magneto-optically manipulated atomic ensemble with a tripod configuration is used to enhance the coupling between systems S and B. The spatial profile of the external fields induces a spatially varying potential for system B in the gas cell with identical and noninteracting atoms at different transverse points. It is found that the coherence of the system S can be maintained, lost or gained by properly choosing the incident positions of the probe field with respect to the center of the control laser field, and the two photon detuning for each components of the probe laser field.     

Sideband manipulation of population inversion in a three-level Λ atomic system

Sideband manipulation of population inversion in a three-level A atomic configuration is investigated theoretically. Compared with the case of a nearly monochromatic field, a population inversion between an excited state and a ground state has been found in a wide sideband intensity range by increasing the difference in frequency between three components. Furthermore, the population inversion can be controlled by the sum of the relative phases of the sideband components of the trichromatic pump field with respective to the phase of the central component. Changing the sum phase from 0 to π, the population inversion between the excited state and the ground state can increase within nearly half of the sideband intensity range. At the same time, the sideband intensity range that corresponds to the system exhibiting inversion ρ00 〉 ρ11 also becomes wider evidently.     

Fast Brillouin Optical Fiber Sensor for Distributed Dynamic Measurement Based on Differential Double-Pulse

We demonstrate a high-spatial-resolution fast Brillouin optical time-domain analysis scheme based on frequency agility and differential double-pulse for distributed dynamic measurement. The frequency-agility probe wave is obtained from the second-order sideband of modulated light by using frequency-agility microwave signal from a wideband arbitrary waveform generator. The differential double-pulse technique is proposed to improve the spatial resolution while keeping the capability of dynamic measurement. In experiment, a spatial resolution of 20 cm is achieved by using a 52/50 ns differential double-pulse, and the distributed vibration measurement is demonstrated over a 50-m Panda fiber with a maximum vibration frequency of up to 50 Hz. With only five averages, the standard deviation of the strain accuracy is of 14 μV.     

Controllable optical response in hybrid opto-electromechanical systems

We theoretically investigate the analog of electromagnetically induced absorption and parametric amplification in a hybrid opto-electromechanical system consisting of an optical cavity and a microwave cavity coupled to a common mechanical resonator. When the two cavity modes are driven by two pump fields, a weak probe beam is applied to the optical cavity to monitor the optical response of the hybrid system, which can be effectively controlled by adjusting the frequency and power of the two pump fields. We find that the analog of electromagnetically induced absorption and parametric amplification can appear in the probe transmission spectrum when one cavity is pumped on its red sideband and another is pumped on its blue sideband. These phenomena can find potential applications in optical switching and signal amplification in the quantum information process.     

Manipulating and imaging the shape of an electronic wave function by magnetotunneling spectroscopy

We measure the current due to electrons tunneling through the ground state of hydrogenic Si donors placed in a GaAs quantum well in the presence of a magnetic field tilted at an angle to the plane of the well. The component of B parallel to the direction of current compresses the donor wave function. By measuring the current as a function of the perpendicular component of B, we probe how the magnetocompression affects the spatial form of the wave function and observe directly the transition from Coulombic to magnetic confinement at high fields.     

Generation of electromagnetic waves in the terahertz frequency range by optical rectification of a Gaussian laser pulse in a plasma in presence of an externally applied static electric field

We propose a theoretical model for the generation of electromagnetic waves in the terahertz (THz) frequency range by the optical rectification of a Gaussian laser pulse in a plasma with an applied static electric field transverse to the direction of propagation. A Gaussian laser pulse can exert a transverse component of the quasi‐static ponderomotive force on the electrons at a frequency in the THz range by a suitable choice of the laser pulse width. This nonlinear force is responsible for the density oscillation. The coupling of this oscillation with the drift velocity acquired by electrons due to the applied static electric field leads to the generation of a nonlinear current density. A spatial Gaussian intensity profile of the laser beam enhances the generated THz yield by many folds as compared to a uniform spatial intensity profile.     

Spectronanoscopy of photonic wires and supercontinuum generation by parametrically coupled Raman sidebands

Within a narrow spectral region around the wavelength of zero-group-velocity dispersion of a nonlinear-optical waveguide, phase-matched four-wave mixing couples the Stokes Raman sideband of a pump field to its anti-Stokes counterpart. This wave coupling suggests a sensitive probe for linear and nonlinear-optical parameters of the waveguide, enabling the detection of nanoscopic size variations of microchannel waveguides in photonic-crystal fibers, and facilitates the generation of broadband supercontinuum radiation.     

Sideband control of optical bistability and multistability

We present sideband control of optical bistability and multistability based on trichromatic electromagnetic-field induced transparency and quantum interference. Appearance or disappearance of the bistability and multistability, manipulation of the hysteresis loop widths, and switching between bistability and tristability are achieved simply by varying the sideband amplitudes or the relative phases of the sidebands to the central component.     

Time-resolved phase-space distributions for light backscattered from a disordered medium

We demonstrate time-resolved measurement of optical phase-space distributions as a new probe for investigating the propagation of light in disordered media. Phase-space techniques measure the joint transverse position and momentum distribution of the scattered light, and are sensitive to the spatially varying phase and amplitude of the field. Using this method we investigate light backscattered from a random medium. The measurements indicate that the weakly localized component is a phase conjugate of the incident light field. A new model of backscatter, based on Wigner phase-space distributions, elucidates the spatial and angular behavior of the localized and unlocalized components.     

Direct nondestructive imaging of magnetization in a spin-1 Bose-Einstein gas

Polarization-dependent phase-contrast imaging is used to resolve the spatial magnetization profile of an optically trapped ultracold gas. This probe is applied to Larmor precession of degenerate and nondegenerate spin-1 87Rb gases. Transverse magnetization of the Bose-Einstein condensate persists for the condensate lifetime, with a spatial response to magnetic field inhomogeneities consistent with a mean-field model of interactions. In comparison, the magnetization of the non-condensed gas decoheres rapidly. Rotational symmetry implies that the Larmor frequency of a spinor condensate be density independent, and thus suitable for precise magnetometry with high spatial resolution.     

Absorption-Amplification Response with or Without Spontaneously Generated Coherence in a Coherent Four-Level Atomic Medium

We discuss and analyze the absorption-amplification properties of a weak probe field in a typical four-level atomic system in the presence of an additional coherence term, the spontaneously generated coherence term. Theinfluences of the spontaneously generated coherence and a coherent pump field on the probe absorption (amplification)are investigated in detail. We show that the absorption of such a weak probe field can be dramatically enhanced dueto the presence of the spontaneously generated coherence. At the same time, the probe-absorption profile exhibitsthe double-peak structure and the probe-absorption peak gradually decreases as the pump intensity increases. On thecontrary, the amplification of such a weak probe field near the line center of the probe transition can be achieved byadjusting the coherent pump field intensity in the absence of the spontaneously generated coherence.     

Absorption-amplification response with or without spontaneously generated coherence effect in a four-level atomic system

We discuss and analyze the absorption properties of a weak probe field in a typical four-level atomic system in the presence of a spontaneously generated coherence (SGC) term. The influences of the SGC and a coherent pump field on the probe absorption-amplification are investigated. The results show that the absorption of such a weak probe field can be dramatically enhanced due to the SGC effect. At the same time, the probe-absorption profile exhibits a two-peak structure and the probe-absorption peak gradually decreases as the pump intensity increases. On the contrary, the amplification of such a weak probe field near the line center of the probe transition can be achieved by adjusting the coherent pump field intensity in the absence of the SGC effect.     

Observation of quantum motion of a nanomechanical resonator

In this Letter we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to near its quantum ground state (phonon occupancy 2.6±0.2), and observe the motional sidebands generated on a second probe laser. Asymmetry in the sideband amplitudes provides a direct measure of the displacement noise power associated with quantum zero-point fluctuations of the nanomechanical resonator, and allows for an intrinsic calibration of the phonon occupation number.