Infrared-light propagation and storing through two lateral tunnel-coupled InGaAs/GaAs quantum dots

Dynamic propagation and storing-retrieving of a weak infrared (IR)-light pulse in a coupled semiconductor double-quantum-dot (SDQD) structure are studied theoretically with feasible parameters. Two characteristic features are found. First, it is shown that, with a constant control field, the SDQD medium is transparent to the probe pulse which propagates over sufficiently long distances. Furthermore, the pulse shape remains unchanged on propagation. Second, with a time-varying control field, we are able to store and retrieve the probe pulse in this four-subband SDQD medium by adiabatically switching off and on the control field. Such a four-subband SDQD system for storing and retrieving coherent information is much more practical than its atomic counterpart as a result of its flexible design and the controllable (tunable) interference strength and thus provides a new possibility for technological applications in quantum information science in the SDQD solid-state nanostructure.     

Delay limit of slow light in an optical fiber

We show that coherent population oscillations effect produces a very narrow spectral hole in the absorption spectrum. The large dispersion of the refractive index associated with this hole permits us to achieve a group velocity as low as 1496.25 m/s at room temperature in an erbium-doped fiber. When the input intensity is equal to the saturation intensity, the dispersion is optimal. The optimal dispersion corresponds to the maximum fractional delay. Therefore, the input intensity can be used as a control parameter to increase the fractional delay. Our theoretical results based on population oscillation agree very well with the experimental data. In addition, we confirm that the spectral hole experiences power broadening for optical fibers of different lengths.     

Control of the switch between optical multistability and bistability in three-level V-type atoms

We theoretically investigated a hybrid absorptive-dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.     

Ultraslow optical solitons in a four-level tripod atomic system

We investigate possible formation and propagation of localized, shape-preserving nonlinear optical pulse in a resonant, lifetime-broadened four-level tripod atomic system via electromagnetically induced transparency (EIT). We prove both analytically and numerically that although in anomalous dispersion regimes near resonance a superluminal optical soliton may appear, such soliton suffers serious absorption. However, by choosing appropriate parameters to make the system work in normal dispersion regimes and within an EIT transparency window, ultraslow optical solitons with very low light intensity can form and propagate stably in the system.     

Evolution of population in an equispaced three-level ladder-type atomic system

Transient response of nearly equispaced three-level ladder-type atomic system with a broad-band squeezed vacuum (SV) is investigated. We focus our attention in the interplay between the quantum interference and the squeezed field on the population distribution. It is shown that an atomic population inversion can be attained on one of the optical transitions due to the SV. Additionally, we show, with the proper value of the relative phase, the SV can also lead to unexpected population inversion on the transition between two different levels.     

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.     

Control of group velocity of light via magnetic field

We have theoretically studied the effects of quantum coherence in a driven quasi-degenerate two-level atomic system. We have shown that the quantum interference, which can be destructive or constructive, can be controlled by an externally applied magnetic field allowing one to implement both electromagnetically induced transparency and electromagnetically induced absorption in the same atomic system. Determined by frequency dispersion of the index of refraction of the system, the group velocity of light pulses ranges from ultra-slow to superluminal with changing of the magnitude of the magnetic field.     

Dynamics of optical switching phenomena in dense media

The ultrafast optical switching phenomena in a dense medium of two-level atoms induced by arbitrary varying pulses are explained in terms of the adiabatic cancellation of the pulse by the induced polarization. The final population inversion of the medium after the passage of the pulse is found to depend on the number of oscillations the inversion exhibits during the time interval when the normalized pulse amplitude exceeds the maximum allowed value of the atomic polarization. If the inversion undergoes an integer number of oscillations in this region, then the final state of the system returns to the ground state. On the other hand, if the inversion undergoes a half integer number of oscillations in this region, the final state of the system is fully inverted. This behavior is explored analytically and illustrated numerically for the constant, sine and secant pulse shapes.     

Coherent control of optical precursors in a warm atomic system with Doppler effects

We theoretically study coherent control of optical precursors via active Raman gain (ARG) in an N-type warm atomic system. When a step pulse passes through an ARG window, main fields are advanced due to fast-light effect and constructively interference with optical precursors, then an enhanced transient pulse appears. As the control field decreases, the interference effect is strengthened, and the transient pulse builds up and becomes narrow. Moreover, its peak intensity is inverse to the system temperature and also determined by the input-pulse form. The scheme may be useful in designing optical devices in optical communication.     

Characterization of nonlinear optical parameters of polymethine dyes

We investigated nonlinear refraction, nonlinear absorption, and saturable absorption of polymethine dyes by the Z-scan technique (λ=1064 nm). The analysis of simultaneous appearance of several nonlinear optical processes in dye solutions excited by picosecond pulses was carried out. The saturable absorption was analyzed taking into account various models. Nonlinear refractive indices, nonlinear absorption coefficients, and saturation intensities of various polymethine dyes were measured. Received: 27 December 2002 / Revised version: 6 March 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +81-471/363-366, E-mail: r_ganeev@issp.u-tokyo.ac.jp RID="**" ID="**"Present address: The Institute for Solid State Physics, The Tokyo University, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan     

Three-Photon Resonant Nondegenerate Six-Wave Mixing in a Dressed Atomic System

We report a three-photon resonant nondegenerate six-wave mixing （NSWM） in a dressed cascade five-level system. It has advantages that phase match condition is not stringent and NSWM signal is enhanced tremendously due to the multiple resonance with the atomic transition frequencies. In the presence of a strong coupling field, the threephoton resonant NSWM spectrum exhibits＂ Autler-Townes splitting. This technique provides a spectroscopic tool for measuring not only the resonant frequency and dephasing rate but also the transition dipole moment between two highly excited atomic states.     

Effect of spontaneously generated coherence on probe response in an open system

The effect of spontaneously generated coherence on the probe response in an open ladder atomic system with equispaced levels is studied. The result shows that by adjusting the strength of spontaneously generated coherence (SGC), electromagnetically induced transparency (EIT) and high dispersion (index of refraction) with zero absorption can be realized, a much larger gain without inversion (GWI) than that without SGC can be obtained. Moreover, in the open system and for some strength of SGC, GWI without the incoherent pumping is much larger than that with the incoherent pumping; however, in the corresponding closed system, when the incoherent pumping is absent, we cannot obtain any gain (with or without inversion) for any strength of SGC. In addition, the manipulation role of the atomic exit and injection rates on SGC-dependent absorption property is analyzed for the case when the incoherence pumping does not exist.     

Transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure

The transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure is reported. The transient process of the system, which is induced by the external coherent coupling field, shows the property of no inverse gain. We find that the transient behavior of the probe field can be tuned by the change of tunneling barrier. Both the amplitude of the transient gain and the frequency of the oscillation can be affected by the lifetime broadening.     

Coherent control of a light field with electromagnetically induced transparency in a dark state Raman coherent tripod system

A dark state superposition is employed and formed a tripod-like system. A weak probe pulse propagates in it can experience a crossover from absorption to transparent and then to amplification, and its group velocity can be controlled in any desired speed by determining the initial states of the dark state superposition.     

Coherent control of optical bistability in tunnel-coupled double quantum wells

We analyze optical bistability (OB) behavior based on intersubband transitions in an asymmetric coupled-quantum well (CQW) driven coherently by a probe laser field and a control laser field by means of a unidirectional ring cavity. We demonstrate that OB can be controlled by tuning the energy splitting between two tunnel-coupled electronic levels, the intensity of the control field, and the frequency detuning of the probe and control fields. The influence of the electronic cooperation parameter on the OB behavior is also discussed. This investigation may be used for optimizing and controlling the optical switching process in the CQW solid-state system, which is much more practical than that in atomic system because of its flexible design and the controllable interference strength.     

Parametric conversion and maximally entangled photon pair via collective excitations in a cycle atomic ensemble

We study the propagation of two quantized optical fields via considering the collective effects of photonic emissions and excitations of a three-level cyclic-type system (such as atomic ensemble with symmetry broken, or the chiral molecular gases, or manual “atomic” array with symmetry broken), where the quantum transitions is driven by two quantized fields and a classical one. The results show that the parametric conversion and maximally entangled photon pair generation can be achieved by means of the collective excitation of the two upper energy levels induced by the classic optical field. This investigation may be used for the generated coherent short-wavelength quantum radiation and quantum information processing.     

Effect of spontaneously generated coherence on Kerr nonlinearity in a four-level atomic system

We propose a scheme for giant enhancement of the Kerr nonlinearity in a four-level atomic system in which spontaneously generated coherence is present. The physics mechanism of the enhancement of Kerr nonlinearity is mainly based on the presence of an extra atomic coherence induced by the spontaneously generated coherence. Numerical values obtained by solving the density matrix equations agree well with these exact analytical values.     

Coherent laser-induced optical behaviors in three-coupled-quantum wells and their application to terahertz signal detection

We investigate quantum optical behaviors of a weak-probe laser field in an asymmetric semiconductor three-coupled-quantum wells (TCQW) structure based on intersubband transitions (ISBTs) via switch-on/off of terahertz (TH) signal radiation under the application of a control laser field. A scheme for TH signal detection and its strength measurement based on this probe absorption characteristic also are put forward, where TH signal field does not interact directly with electron, but significantly affects the coherent optical absorption properties of such a weak-probe laser field. Consequently, the proposed TCQW nanostructure may be used for reducing and cancelling out the important thermionic dark current component in the process of TH signal detection, measurement and photodetector design.     

Comparison of transient process between open and closed ladder-type systems with spontaneously generated coherence and incoherent pumping

We theoretically investigated transient response of open and closed three-level ladder-type atomic system with or without the spontaneously generated coherence (SGC) which could be satisfied with the help of an incoherent pumping. The existence of the SGC effect makes the open and closed system to be distinguished. We compared transient response of weak probe between open and closed system and found that transient properties exhibit different features by adjusting some related parameters, such as the relative phase between probe and coupling fields, the angle between two dipole moments.     

Coherent control of laser pulse temporal duration: An experimental proposal

We present a study of temporal compression resulting from the coherent control peculiarities of electromagnetically induced transparency propagation dynamics. We discuss the crucial conditions required to accomplish temporal compression in an experiment with a sample of hot atoms.