Weak Optical Fields Research Articles

Multi-mode cross-Kerr interaction and three-qubit all-optical logic gates in a triple electromagnetically induced transparency system

We investigate the nonlinear interaction of weak optical fields in triple electromagnetically induced transparency (EIT) where EIT is induced simultaneously for three weak slow light pulses. Different kinds of nonlinear interaction including two-mode cross-Kerr interaction, three-mode cross-Kerr interaction, high order two-mode cross-Kerr interaction and hybrid high order two-mode cross-Kerr interaction can be obtained under certain conditions. These nonlinear interactions have promise for a realistic scheme of photon logic gates necessary for practical implementation of quantum information processing.

Dielectric Nano-Systems with Unique Optical Properties

The study of optical properties of Al2O3, SiO2, TiO2, and ZnO nanoparticles in weak optical fields is presented. We found that some nanoparticles have unique optical nonlinearity: The values of portions to nanoparticle refractive index and absorption coefficient increase to maxima, and then decrease to zero when the radiation intensity changes from 1 to 500 W/cm2. We estimated electron energy structures of nanoparticles and experimentally determined that such nonlinearity is directly related to peculiarities of the energy structure. We obtained a good fitting of theoretical results to the experimental ones (e.g. absorbance spectra of nanoparticles; the dependence of nanoparticle refractive index and absorption coefficient on radiation intensity).

Steady-state, cavityless, multimode superradiance in a cold vapor

We demonstrate steady-state, mirrorless superradiance in a cold vapor pumped by weak optical fields. Beyond a critical pump intensity of 1 mW/cm$^2$, the vapor spontaneously transforms into a spatially self-organized state: a density grating forms. Scattering of the pump beams off this grating generates a pair of new, intense optical fields that act back on the vapor to enhance the atomic organization. We map out experimentally the superradiant phase transition boundary and show that it is well-described by our theoretical model. The resulting superradiant emission is nearly coherent, persists for several seconds, displays strong temporal correlations between the various modes, and has a coherence time of several hundred $\mu$s. This system therefore has applications in fundamental studies of many-body physics with long-range interactions as well as all-optical and quantum information processing.

Optical vortex filtering for the detection of electromagnetically induced transparency

We report on the realization of an optical filter based on an optical vortex mask designed to exclusively detect a weak coherent laser field in the presence of a much stronger, nearly spatially overlapping field. We demonstrate the performance of such an optical vortex filter to eliminate the strong control field and detect only a weak optical field's transmission under the conditions of electromagnetically induced transparency. The attractive feature of such a filter is its insensitivity to optical field frequencies and polarizations, which makes it applicable for a wide range of coherent processes.

Nonlinear Faraday rotation in electromagnetically induce transparency medium

By using multiple-scale methods, we study analytically the propagation properties of the weak linear polarization probe optical field in a cold lifetime-broadened five-level V type atomic system via electromagnetically induced transparency. It is shown that with the strength of the coupling field increasing, the absorption of the probe optical field decreases rapidly and the group velocity of the probe optical field increases quickly under the consideration of linear effect. However, the velocity is several orders of magnitude slower than the light speed in vacuum. Meanwhile, we find that for the same magnetic field the nonlinear Faraday rotation direction is opposite to linear Faraday rotation, and its rotation angle grows bigger than that of linear Faraday rotation. These results mean that the Faraday rotation of the electromagnetically induced transparency medium can be controlled by the nonlinear effect.

Confined Optical Fields in Nanovoid Chain Structures Directly Visualized by Near-Field Optical Imaging

Linearly aligned nanovoid chain structures on Au thin films were fabricated on glass substrates. Two-photon excitation imaging techniques using an aperture-type near-field scanning optical microscope revealed localized optical field distributions due to the individual structures. Confined optical fields due to the void chains were observed at each interstitial gap between voids with excitation polarization parallel to the chain axis. Electromagnetic field simulations of dimeric voids qualitatively matched the experimental results. Under excitation polarization perpendicular to the chain axis, only weak optical fields were observed. Further detailed characteristics of localized optical fields in these systems, including those in relation to Babinet’s principle in optics, were discussed. Our study may open up new possibilities in molecular sensing and photochemistry.

Giant cross-Kerr nonlinearity in carbon nanotube quantum dots with spin-orbit coupling

We investigate the nonlinear interaction between two weak optical fields in carbon nanotube quantum dots based on electromagnetically induced transparency and spin-orbit coupling. Our results show, owing to the energy differences produced by strong spin-orbit coupling, that a giant cross-Kerr nonlinearity can be achieved with group-velocity matching, while the probe- and signal-fields absorptions are suppressed simultaneously. We demonstrate that such enhanced nonlinear optical effects can be employed to implement controlled-phase gate between pairs of single-photon pulses with high fidelity and to generate entanglement of coherent Schr\odinger-cat states.

Single Charged Quantum Dot in a Strong Optical Field: Absorption, Gain, and the ac-Stark Effect

We investigate a singly charged quantum dot under a strong optical driving field by probing the system with a weak optical field. We observe all critical features predicted by Mollow for a strongly driven two-level atomic system in this solid state nanostructure, such as absorption, the ac-Stark effect, and optical gain. Our results demonstrate that even at high optical field strengths the electron in a single quantum dot with its dressed ground state and trion state behaves as a well-isolated two-level quantum system.

Optical Bistability at Low Light Level due to Collective Atomic Recoil

We demonstrate optical nonlinearities due to the interaction of weak optical fields with the collective motion of a strongly dispersive ultracold gas. The combination of a recoil-induced resonance in the high gain regime and optical waveguiding within the dispersive medium enables us to achieve a collective atomic cooperativity of 275+/-50 even in the absence of a cavity. As a result, we observe optical bistability at input powers as low as 20 pW. The present scheme allows for dynamic optical control of the dispersive properties of the ultracold gas using very weak pulses of light. The experimental observations are in good agreement with a theoretical model.

Equivalence of second-order sub-Poissonian statistics and fourth-order squeezing for intense light

We study the simultaneous occurrence of second-order sub-Poissonian photon statistics and fourth-order squeezing for the operator Xθ = X1cosθ+X2sinθ, in the displaced state , where the Hermitian operators X1,2 are defined by X1+i X2 = a, the annihilation operator, D(α) = exp(αa+−α*a) is the displacement operator, α = |α|ei θ and is the state of the weak optical field. We show that the two phenomena occur simultaneously when the amplitude |α| of the displacement is very large as compared to the amplitude of the weak optical field. We also propose a balanced homodyne method for detection of fourth-order squeezed light in the same fashion as that for normal squeezing.

Electromagnetically induced transparency: Optics in coherent media

Coherent preparation by laser light of quantum states of atoms and molecules can lead to quantum interference in the amplitudes of optical transitions. In this way the optical properties of a medium can be dramatically modified, leading to electromagnetically induced transparency and related effects, which have placed gas-phase systems at the center of recent advances in the development of media with radically new optical properties. This article reviews these advances and the new possibilities they offer for nonlinear optics and quantum information science. As a basis for the theory of electromagnetically induced transparency the authors consider the atomic dynamics and the optical response of the medium to a continuous-wave laser. They then discuss pulse propagation and the adiabatic evolution of field-coupled states and show how coherently prepared media can be used to improve frequency conversion in nonlinear optical mixing experiments. The extension of these concepts to very weak optical fields in the few-photon limit is then examined. The review concludes with a discussion of future prospects and potential new applications.

High-Resolution Laser Spectroscopy of Methane

Detection of atmospheric methane is based on a huge amount of fundamental data provided by high-resolution spectroscopy in the infrared region. Doppler-limited and sub-Doppler resolution spectroscopy of methane have been discussed in particular for the 3.3 and 1.67μm band transitions. To attain sub-Doppler resolution in the 1.67μm band transitions, we employed a Fabry Perot cavity as an absorption ce11. This enabled us to observe nonlinear saturation spectra with a spectral resolution of about 1 MHz even using the weak optical field from a laser diode, because the optical field strength in the cavity is greatly enhanced at the antinodes of the optical standing wave. We precisely measured small Stark shifts of seven tetrahedral components of the vibration rotation transitions, sixty-six difference frequencies between the components, and the absolute frequency of two transitions. To enhance the sensitivity, noise-immune cavity-enhanced optical- heterodyne molecular spectroscopy (NICE-OHMS) was also applied.

Resonance fluorescence in photonic band gap waveguide architectures: Engineering the vacuum for all-optical switching

We describe the spectral characteristics of the radiation scattered by two-level atoms (quantum dots) driven by a strong external field, and coupled to a photonic crystal radiation reservoir. We show that in the presence of strong variations with the frequency of the photonic reservoir density of states, the atomic, Mollow, sideband components of the scattered intensity can be strongly modified. Consequently, a weak optical probe field experiences a substantial differential gain in response to slight variations in the intensity of an optical driving field. We suggest that these effects may be of relevance to all-optical transistor action in photonic crystals. Using a specific photonic crystal heterostructure, we suggest that an all-optical microtransistor based on photonic crystals may operate at less than $100\phantom{\rule{0.3em}{0ex}}\text{nW}$ switching threshold power. Collective $N$-atom effects substantially enhance this optical switching effect. Near the switching threshold intensity, collective effects are manifest in the ${N}^{2}$ scaling of the intensity spectrum (reminiscent of superradiance). Above and below this critical region, the gain spectrum widens (linearly with $N$). This correspondingly reduces the switching time scales of the atomic system in response to external fields. Furthermore, the quantum degree of second-order coherence exhibits unusual features. Scattered photons display a variable degree of antibunching as function of driving laser field intensity and the photonic density of states discontinuity. We analyze the effects of the inhomogeneous atomic line broadening on the amplification process. We show, using suitable photonic density of states engineering, that it is possible to select a narrow spectral range around the central frequency of the atomic frequency distribution over which amplification and switching occur. This is done either by spectral decoupling of the active elements from the electromagnetic field (through the introduction of band gaps at specified spectral locations) or through incoherent pumping to selectively saturate atoms outside the spectral region chosen for amplification.

Binomial states and the phase distribution measurement of weak optical fields

We show that the eight-port interferometer used by Noh, Foug\`{e}res, and Mandel [Phys. Rev. Lett. {\bf 71}, 2579 (1993)] to measure their operational phase distribution of light can also be used to measure the canonical phase distribution of weak optical fields, where canonical phase is defined as the complement of photon number. A binomial reference state is required for this purpose, which we show can be obtained to an excellent degree of approximation from a suitably squeezed state. The proposed method requires only photodetectors that can distinguish among zero, one and more than one photons and is not particularly sensitive to photodetector imperfections.

Towards high‐fidelity two‐photon quantum communications

AbstractWe propose two alternative scheme for highly efficient nonlinear interaction between weak optical fields. The first scheme is based on the attainment of electromagnetically induced transparency simultaneously for two fields via transitions between magnetically split F = 1 atomic sublevels, in the presence of two driving fields. The second scheme relies on simultaneous electromagnetically‐ and self‐induced transparencies of the two fields. Thereby, equal slow group velocities and giant cross‐phase modulation of the weak fields over long distances are achieved.

Atomic-vapor-based high efficiency optical detectors with photon number resolution.

The ability to detect very weak optical fields with high efficiency (>99%) and to distinguish the number of photons in a given time interval is a very challenging technical problem with enormous potential payoffs in quantum communications and information processing. We propose to employ an atomic vapor as the active medium, prepared in a specific quantum state using laser radiation. The absorption of a photon will be aided by a dressing laser, and the presence or absence of an excited atom will be detected using the "cycling transition" approach perfected for ion traps. By incorporating an appropriate up-conversion scheme, our method can be applied to a wide variety of optical wavelengths.

Symmetric photon-photon coupling by atoms with Zeeman-split sublevels

We propose a simple scheme for highly efficient nonlinear interaction between two weak optical fields. The scheme is based on the attainment of electromagnetically induced transparency simultaneously for both fields via transitions between magnetically split F=1 atomic sublevels, in the presence of two driving fields. Thereby, equal slow group velocities and symmetric cross-coupling of the weak fields over long distances are achieved. By simply tuning the fields, this scheme can either yield giant cross-phase modulation or ultrasensitive two-photon switching.

Nonperturbative terahertz-field interactions in semiconductor quantum wires

We model high-field dynamic electro-optical effects in semiconductor quantum wires. Our nonperturbative, time-dependent studies employ weak optical pulses and strong terahertz fields such as are available from free-electron lasers. Three remarkably strong effects are demonstrated: (1) a strong Autler-Townes splitting of the $1s$ exciton resonance via intraband exciton coupling, (2) phase-dependent two-photon induced gain just above the band gap, and (3) high-field harmonic generation in the THz regime.

Phase control of group velocity: From subluminal to superluminal light propagation

We show that the group velocity of a weak pulse can be manipulated by controlling the phases of two weak optical fields applied to a V-shaped three-level system. Such control can even cause the probe propagation to change from subluminal to superluminal. We consider two schemes: in the first, the excited states are coupled by decay-induced coherence, which is an inherent property of the medium, and in the second, quantum coherence is created by coupling the excited states to each other by a strong microwave field. We also discuss the group velocity reduction experienced by a single weak propagating probe due to decay-induced coherence.

Exciton absorption in semiconductor quantum wells driven by a strong intersubband pump field

Optical interband excitonic absorption of semiconductor quantum wells (QW’s) driven by a coherent pump field is investigated on the basis of semiconductor Bloch equations. The pump field has a photon energy close to the intersubband spacing between the first two conduction subbands in the QW’s. An external weak optical field probes the interband transition. The excitonic effects and pump-induced population redistribution within the conduction subbands in the QW system are included. When the density of the electron–hole pairs in the QW structure is low, the pump field induces an Autler–Townes splitting of the exciton absorption spectrum. The split size and the peak positions of the absorption doublet depend not only on the pump frequency and intensity but also on the carrier density. As the density of the electron–hole pairs is increased, the split contrast (the ratio between the maximum and the minimum values) is decreased, because the exciton effect is suppressed at higher densities owing to the many-body screening.