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A coherently prepared Er3+-doped yttrium aluminum garnet (YAG) crystal with a four-level ionic configuration is exploited for realizing one-dimensional (1D) and two-dimensional (2D) electromagnetically induced gratings (EIGs). Owing to the probe gain induced by the incoherent pump, the diffraction efficiency of the crystal grating, especially the first-order diffraction, can be significantly improved via increasing the incoherent pumping rate or decreasing the probe detuning. The enhancement of the grating diffraction efficiency originates from the interference between the gain and phase gratings. It is also demonstrated that the diffraction of the crystal grating can be dynamically controlled via tuning the intensity and detuning of the standing-wave driving field or the concentration of Er3+ ion. More importantly, the probe energy of the diffraction side lobes around the central principle maximum is comparable to that of the first-order diffraction field for small driving intensity or large driving detuning. Our scheme may provide a possibility for the active all-optical control of optical switching, routing and storage in fiber communication wavelengths.

A scheme for the coherent control of perfect optical vortex (POV) in an asymmetric semiconductor double quantum well (SDQW) nanostructure is proposed by exploiting the tunneling-induced highly efficient four-wave mixing (FWM). The orbital angular momentum (OAM) is completely transferred from a unique POV mode to the generated FWM field. Using experimentally achievable parameters, we identify the conditions under which resonant tunneling allows us to improve the quality of the vortex FWM field and engineer helical phase wave front beyond what is achievable in the absence of resonant tunneling. Furthermore, we find that the intensity and phase patterns of the vortex FWM field are sensitive to the detuning of the probe field but rather robust against the detuning of the coupling field. Subsequently, we perform the coaxial interference between the vortex FWM field and a same-frequency POV beam and show interesting interference properties, which allow us to measure the topological charge of the output POV beam. Our result may find potential applications in quantum technologies based on POV in solids.

We propose a potentially practical scheme for realizing ultrasensitive size sensor of a single metallic nanoparticles (MNP) in a hybrid nonlinear microcavity. This is achieved by exploiting a well-established microcavity-engineered plasmonic resonance, where a degenerate parametric amplifier (DPA) is embedded into the microcavity driven by a strong pump field and a weak probe pulse. It is shown that the transmission spectrum of the probe pulse exihibits a two-peak splitting and the splitting width depends on the radius. The radius of a single MNP can be inferred from the transmission spectrum by monitoring the width between two peaks. Using experimentally achievable parameters, we identify the detection sensitivity of the sensor can reach approximately 0.198 THz/nm for detecting and sizing of individual MNPs as small as 10 nm in radius.

We propose a potentially practical scheme for the controllable single-photon transport via waveguides which are coupled to a microcavity–emitter system. The microcavity–emitter system consists of a V-type three-level emitter and two or one single-mode microcavity. A driving field is used to drive a hyperfine transition between two upper excited states of the V-type three-level emitter. Beyond chiral coupling between waveguides and microcavity–emitter system, we show that the perfectly nonreciprocal single-photon transport in a single waveguide and the single-photon router with 100% routing probability in two waveguides can be achieved. Interesting enough, whether the nonreciprocal single-photon transport or the single-photon router can be switched periodically by adjusting the phase associated with microcavity–emitter coupling strength and the driving field. The complete physical explanation of the underlying mechanism is presented.

The photon router plays an essential role in the optical quantum network. However, conventional routers generally couple photons chirally into waveguides to achieve complete transmission from the input port to the required port. Here, we use non-chiral photon-atom interactions for targeted routing. The system consists of two V-type three-level atoms and two parallel waveguides. In addition, the two atoms are driven by external coherent fields, respectively. With a real-space Hamiltonian, the probability of photon transmitted to four ports can be obtained. The study shows that a single photon input from the left port of the waveguide-a can be deterministically transferred to any of the four ports of the two waveguides by adjusting the detuning of the atom and the driving field on the atom, as well as the distance between the two atoms.

We analyze the destructive interference in monolayer graphene under Landau quantization in a time-dependent way by using the Bloch-Maxwell formalism. Based on this analysis, we investigate the dynamics control of an infrared probe and a terahertz (THz) switch pulses in graphene. In presence of the THz switch pulse, the destructive interference take places and can be optimized so that the monolayer graphene is completely transparent to the infrared probe pulse. In absence of the THz switch pulse, however, the infrared probe pulse is absorbed due to such a interference does not take place. Furthermore, we provide a clear physics insight of this destructive interference by using the classical dressed-state theory. Conversely, the present model may be rendered either absorbing or transparent to the THz switch pulse. By choosing appropriate wave form of the probe and switch pulses, we show that both infrared probe and THz switch pulses exhibit the steplike transitions between absorption and transparency. Such steplike transitions can be used to devise a versatile quantum interference-based solid-state optical switching with distinct wave-lengths for optical communication devices.

A coherently prepared Er3+-doped yttrium aluminum garnet (YAG) crystal with a four-level ionic configuration is exploited for realizing one-dimensional (1D) and two-dimensional (2D) electromagnetically induced gratings (EIGs). Owing to the probe gain induced by the incoherent pump, the diffraction efficiency of the crystal grating, especially the first-order diffraction, can be significantly improved via increasing the incoherent pumping rate or decreasing the probe detuning. The enhancement of the grating diffraction efficiency originates from the interference between the gain and phase gratings. It is also demonstrated that the diffraction of the crystal grating can be dynamically controlled via tuning the intensity and detuning of the standing-wave driving field or the concentration of Er3+ ion. More importantly, the probe energy of the diffraction side lobes around the central principle maximum is comparable to that of the first-order diffraction field for small driving intensity or large driving detuning. Our scheme may provide a possibility for the active all-optical control of optical switching, routing and storage in fiber communication wavelengths.

Two-dimensional (2D) optical lattices of driven cold atoms can provide a useful platform to construct 2D electromagnetically induced grating (EIG) with parity-time (PT) antisymmetry. This atomic grating is achieved by the spatial modulations of the atomic density and frequency detunings in the four-level double-Λ atomic system. Gain-assisted PT antisymmetry allows us to realize lop-sided Raman–Nath diffraction with high diffraction efficiency at the exception point. It is shown that the nontrivial phenomenon originates from non-Hermitian degeneracy of PT antisymmetry. Our scheme may provide the possibility for active all-optical control and conversion of the spatial beam in optics.

We investigate the effect of doped E r 3 + ion concentration on an electromagnetically induced grating in an E r 3 + -doped yttrium aluminum garnet (YAG) crystal. Due to the change of electric dipole moment and spontaneous emission decay induced by E r 3 + ion concentration, the Fraunhofer diffraction of the solid-state grating is sensitively dependent upon E r 3 + ion concentration. The three-level E r 3 + ion system with a closed loop leads to probe gain appearing in some concentrations of the E r 3 + ion, which significantly improves the first-order diffraction efficiency of the solid-state grating. Furthermore, it is demonstrated that the relative phase, signal detuning, and grating thickness have different effects on the first-order diffraction efficiency of the solid-state grating under different concentrations of the E r 3 + ion. Therefore, our scheme may provide a basis for selecting a suitable concentration to realize high-efficiency optical switching and routing in future integrated systems.

The sign of quantum interference (constructive or destructive) based on cavity optomechanics is crucial for observing quantum phenomena and designing high-sensitivity sensors with an integrable structure. Here, we propose an efficient scheme to generate constructive interference and optomechanically induced absorption (OMIA) in a hybrid atom–cavity optomechanical system. Using experimentally achievable parameters, we theoretically demonstrate that a gain-type OMIA dip with the extremely narrow linewidth and the enhanced spectral intensity can be modulated by an assisted atom that is excited by an external control field. More importantly, we report that a precise mass sensor is achieved by employing an observable correlation between the OMIA dip and the added mass deposited on the mechanical object. With the help of the back-action cooling of the mechanical object, we identify that the detection sensitivity and minimum resolution of the mass sensor can reach 3.14 MHz / ng and 1 fg, respectively.

We propose a potentially practical scheme for constructing a quantum network based on a system where three waveguides are coupled to two two-level atoms. In the case of chiral couplings between the waveguides and atoms, we realize a directed single-photon router and the efficiency of single-photon routing reaches 100%. In addition, in this network, the photon input from one port of the channel can be fully routed to any outport of the other two channels by modulating the coupling strength of the waveguides and atoms and the frequency of the incident photon. Thus, a quantum network can be constructed based on our scheme. The influence of the ratio of chiral coupling strength on the properties of the single-photon router is also shown. We also show how the efficiency of routing is affected by system dissipation.

We investigate the force measurement sensitivity in a squeezed dissipative optomechanics within the free-mass regime under the influence of shot noise (SN) from the photon number fluctuations, laser phase noise from the pump laser, thermal noise from the environment, and optical losses from outcoupling and detection inefficiencies. Generally, squeezed light could generate a reduced SN on the squeezed quadrature and an enlarged quantum backaction noise (QBA) due to the antisqueezed conjugate quadrature. With an appropriate choice of phase angle in homodyne detection, QBA is cancellable, leading to an exponentially improved measurement sensitivity for the SN-dominated regime. By now, the effects of laser phase noise that is proportional to laser power emerge. The balance between squeezed SN and phase noise can lead to an sub-SQL sensitivity at an exponentially lower input power. However, the improvement by squeezing is limited by optical losses because high sensitivity is delicate and easily destroyed by optical losses.

We theoretically investigate the enhanced charge-dependent generation of the optical second-order sidebands (OSS) in a gain-cavity-assisted optomechanical (GCAOM) system coupled to a charged object. The hybrid optomechanical system is coherently driven by an external two-tone laser field which consists of a continuous-wave pump field and a pulsed probe field. Beyond the conventional linearized description of optomechanical interactions, the nonlinear optomechanical interactions are included in the Heisenberg-Langevin equations and are treated analytically by means of the perturbation method. It is shown that an assisted gain cavity can significantly enhance the OSS generation and can also lead to higher charge dependence of the output OSS spectrum than that achieved from a lossy cavity optomechanical system. Subsequently we discuss the application of such a GCAOM system as a family of high-sensitivity sensor for measuring the charges. Using experimentally achievable parameters, we identify the conditions under which the assisted gain cavity allows us to enhance the OSS generation and improve sensitivity of the sensor beyond what is achievable in a lossy cavity optomechanical system. The present investigation may provide a route toward modulating the nonlinear optical properties of the electro-optic hybrid system, as well as to guide the design of sensitive devices.

We propose and analyze an efficient scheme for the lopsided Raman-Nath diffraction of one-dimensional ($1\mathrm{D}$) and two-dimensional ($2\mathrm{D}$) atomic gratings with periodic parity-time ($\mathcal{PT}$)-symmetric refractive index. The atomic grating is constructed by the cold-atomic vapor with two isotopes of rubidium, which is driven by weak probe field and space-dependent control field. Using experimentally achievable parameters, we identify the conditions under which $\mathcal{PT}$-symmetric refractive index allows us to observe the lopsided Raman-Nath diffraction phenomenon and improve the diffraction efficiencies beyond what is achievable in a conventional atomic grating. The nontrivial atomic grating is a superposition of an amplitude grating and a phase grating. It is found that the lopsided Raman-Nath diffraction at the exceptional point (EP) of $\mathcal{PT}$-symmetric grating originates from constructive and destructive interferences between the amplitude and phase gratings. Furthermore, we show that the $\mathcal{PT}$-phase transition from unbroken to broken $\mathcal{PT}$-symmetric regimes can modify the asymmetric distribution of the diffraction spectrum and that the diffraction efficiencies in the non-negative diffraction orders can be significantly enhanced when the atomic grating is pushed into a broken $\mathcal{PT}$-symmetric phase. In addition, we also analyze the influence of the grating thickness on the diffraction spectrum. Our scheme may provide the possibility to design a gain-beam splitter with tunable splitting ratio and other optical components in integrated optics.

We analyze the optical steady-state behaviors based on intersubband transitions in a triple quantum well structure driven coherently by a probe laser field and two control laser fields embedded in a unidirectional cavity. It is shown that the optical bistability behavior can be observed and controlled efficiently through the frequency detuning of the probe field, the intensities of two control fields, the electronic cooperation parameter, and the Fano-type interference. More interestingly, with Fano-type interference, switch from optical bistability to optical multistability or vice versa can be also controlled by adjusting the relative phase between two coherent control fields.

We propose an efficient scheme to generate quadrature squeezing of a higher-order sideband spectrum in an optomechanical system. This is achieved by exploiting a well-established optomechanical circumstance, where a second-order nonlinearity is embedded into the optomechanical cavity driven by a strong control field and a weak probe pulse. Using experimentally achievable parameters, we demonstrate that the second-order nonlinearity intensity and the frequency detuning of a control field allow us to modify the amplitude of higher-order sidebands and improve the amount of squeezing of a higher-order sideband spectrum. Furthermore, in the presence of a strong second-order nonlinearity, an optimizing quadrature squeezing of a higher-order sideband spectrum can be achieved, which provides a practical opportunity to design the squeezed frequency combs and other precision measurements.

We propose an efficient scheme for the controllable amplification of two-phonon higher-order sidebands in a quadratically coupled optomechanical system. In this scheme, a strong control field and a weak probe pulse are injected into the cavity, and the membrane located at the middle position of the cavity is driven resonantly by a weak coherent mechanical pump. Beyond the conventional linearized approximation, we derive analytical expressions for the output transmission of probe pulse and the amplitude of second-order sideband by adding the nonlinear coefficients into the Heisenberg-Langevin formalism. Using experimentally achievable parameters, we identify the conditions under which the mechanical pump and the frequency detuning of control field allow us to modify the transmission of probe pulse and improve the amplitude of two-phonon higher-order sideband generation beyond what is achievable in absence of the mechanical pump. Furthermore, we also find that the higher-order sideband generation depends sensitively on the phase of mechanical pump when the control field becomes strong. The present proposal offers a practical opportunity to design chip-scale optical communications and optical frequency combs.

We propose and analyze an effective scheme to enhance the optical higher-order sideband generation in a three-cavity array with local parity-time ($\mathcal{PT}$) symmetry. In this three-cavity configuration, a single cavity containing a quantum dot (QD) is coupled to an assisted $\mathcal{PT}$-symmetric combination of two cavities. Beyond the weak-excitation approximation, we derive the analytic formulas used to determine the nonlinear coefficient of the optical second-order sideband (OSS) by employing the perturbation technique. Using experimentally achievable parameters, we identify the conditions under which the assisted $\mathcal{PT}$-symmetric double-cavity system allows us to modify the transmission of the probe field and improve the efficiency of OSS generation beyond what is achievable in a loss-only QD-cavity system. We examine the influence of the $\mathcal{PT}$ phase transition from unbroken- to broken-$\mathcal{PT}$ regimes on the OSS generation. It is found that the efficiency of optical second-order sideband generation can be significantly enhanced when the assisted double-cavity system is in $\mathcal{PT}$-symmetric phase, extremely in the vicinity of the transition point. The present results illustrate the potential to utilize $\mathcal{PT}$-symmetric physical systems for enhancing optical higher-order sidebands and controlling optical frequency combs, as well as to guide the design of experimental implementation.

The effects from quantum coherence via decays and incoherent pumping on the lasing without inversion (LWI) are investigated in a four-level system. By analyzing the transient and steady-state behaviors of the absorption, we find that the gain occurs when both spontaneously generated coherence (SGC) and coherence induced by incoherent pumping (IPC) are considered. We attribute the occurrence of the gain to the interaction of quantum coherence via decays and incoherent pumping.

We investigate the generation and the evolution of continuous-variable (CV) entanglement from a laser-driven four-state atom inside a doubly resonant cavity under Raman excitation. Two transitions in the four-state atom independently interact with the two cavity modes, while two other transitions are driven by coupling laser fields. By including the atomic relaxation as well as cavity losses, we show that the CV entanglement with large mean number of photons can be generated in our scheme. We also show that the intensity of the coupling laser fields can influence effectively the entanglement period of the cavity field. Different from the conventional resonant excitation scheme where zero one-photon detuning are required, it is found that the intensity and period of entanglement between the two cavity modes as well as the total mean photon number of the cavity field can be adjusted by properly modulating the frequency detuning.

The giant enhancement of Kerr nonlinearity in a four-level inverted-Y atomic system is investigated theoretically. Compared with that generated in a generic three-level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. The physical mechanism leading to the giant enhancement of Kerr nonlinearity is also discussed.

We propose a scheme for high-precision two-dimensional (2D) atom localization via the four-wave mixing (FWM) in a four-level double- atomic system. Due to the position-dependent atom-field interaction, the 2D position information of the atoms can be directly determined by the measurement of the normalized light intensity of output FWM-generated field. We further show that, when the position-dependent generated FWM field has become sufficiently intense, efficient back-coupling to the FWM generating state becomes important. This back-coupling pathway leads to competitive multiphoton destructive interference of the FWM generating state by three supplied and one internally generated fields. We find that the precision of 2D atom localization can be improved significantly by the multiphoton destructive interference and depends sensitively on the frequency detunings and the pump field intensity. Interestingly enough, we show that adjusting the frequency detunings and the pump field intensity can modify significantly the FWM efficiency, and consequently lead to a redistribution of the atoms. As a result, the atom can be localized in one of four quadrants with holding the precision of atom localization.

We perform a time-dependent analysis of continuous wave (cw) four-wave mixing (FWM) in InGaAs/AlAs coupled double quantum well (CDQW) structures via intersubband transitions. By using the coupled Schrodinger-Maxwell approach, we obtain the corresponding explicit analytical expressions for the input probe and FWM-generated signal fields. We calculated the dependencies of the efficiency of the FWM-generated fields on cw pump fields and the depths of penetration into the CDQW sample. Such a nonlinear optical process may be used to generate coherent short-wavelength radiation efficiently in the CDQW solid state system.

We study ultrafast excitonic population inversion resulting from the interaction of a semiconductor quantum dot (SQD) with localized surface plasmons. The plasmonic enhanced fields are generated when a metallic nanoparticle (MNP) is subject to a nonlinear chirped few-cycle pulse train. By numerically solving the time-dependent Bloch equations beyond the rotating-wave approximation, we show that the complete population inversion can be achieved for small interparticle distance and the dynamic in population inversion exhibits a steplike transition between absorption and amplifying. This phenomenon can be exploited as an all-optical ultrafast switching device. Moreover, the final state of population inversion is shown to be modified significantly with the interparticle distances, which is not only robust against the variation of probe pulse parameters but also suggests a straightforward method for measuring the interparticle distances via probing the final populations.

We report experimental observation of lasing on surface states, in the form of standing waves at the termination of a defect-free photonic crystal on top of vertical-cavity surface-emission lasers. Direct images of lasing modes at the truncated periodic potential, along one side of a square lattice, are demonstrated by collecting near-field radiation patterns, as well as in numerical simulations. Our results provide a step toward realizing surface and edge states in optical cavities.

With a detailed series of spontaneous optical pattern formations, we reveal the existence of thermodynamical properties in nonlinear optical systems by defining the configurational entropy from the measured patterns. A phase diagram for pattern transitions in the form of stripes, reoriented stripes, hexagons, and spots is reported experimentally and theoretically for incoherent beams in non-instantaneous anisotropic photorefractive crystals, with demonstrations in the boundary of mixed-phase states. Emergence of optical pattern transitions is shown to occur at the local minimum values of effective optical temperature, and accompanied with the change of chemical potentials.

Considering two-level media in the array of weakly coupled nano-cavities, we reveal a variety of dynamical regimes, such as diffusion, self-trapping, soliton, and breathers for the wave-packets in the presence of photon tunneling processes between the next-nearest cavities. We focus our attention on the low branch (LB) bright polariton soliton formation, due to the two-body polariton-polariton scattering processes. When detuning frequency is manipulated adiabatically, the low-branch lattice polariton localized states, i.e., that are solitons and breathers evolving between photon-like and matter-like states, are shown to act as carriers for spatially distributed storage and retrieval of optical information., Comment: 10 pages, 7 figures

We propose and analyze an efficient way to detect the terahertz (THz) signal in a magnetized graphene system via electromagnetically induced transparency. Such a scheme for THz signal detection mainly relies on the measurement of probe transmission spectra, in which the behaviors of a weak-probe transmission spectra can be controlled by switching on/off the THz signal radiation. Taking into account the tunable optical transition frequency between the Landau levels in graphene, our analytical results demonstrate that a broad frequency bandwidth of the THz signal radiation, ranging from 0.36 to 11.4 THz, can be inspected and modulated by means of an external magnetic field. As a consequence, the proposed magnetized graphene system performs a striking potential to utilize quantum interference in the design of optical solid-state devices.

We study the low-intensity light pulse propagation through an asymmetric double quantum well via Fano-type interference based on intersubband transitions. The propagation of the pulse across the quantum well is studied analytically and numerically with the coupled Maxwell-Schr\"odinger equations. We show the generation of ultraslow bright and dark optical solitons in this system. Whether the solitons are dark and bright can be controlled by the ratio of dipole moments of the intersubband transitions. Such investigation of ultraslow optical solitons in the present work may lead to important applications such as high-fidelity optical delay lines and optical buffers in semiconductor quantum wells structure.

A scheme of enhanced four-wave mixing (FWM) signal is exploited in graphene under an external magnetic field via multiphoton quantum destructive interference. By solving the coupled Schrodinger–Maxwell formalism, a time-dependent analysis performs the integrated analytical expressions of the input probe pulse and generated FWM field. Taking into account the tunable optical transition frequency between the Landau levels (LLs) in graphene, it is found that the generated FWM signal in the infrared region can be significantly enhanced and its efficiency is nearly . As a result, the proposed magnetised graphene system may provide a striking potential for generating long-wavelength radiation.

We investigate the high-order harmonic generation (HHG) in a semiconductor quantum dot (SQD) and metallic nanorod (MNR) complex driven by a moderate intensity (10(12) W/cm(2)) frequency-chirped Gaussian few-cycle pulse. Our numerical results indicate that the cutoff energy of the HHG can be controlled by optimizing the shape of the MNR and surface-to-surface distance between the SQD and the MNR. We also show that the extreme ultraviolet supercontinuum harmonics (25 eV maximal photon energy) and isolated ultrashort pulses (2.67-4.36 fs FWHM) are achievable.

We propose an efficient four-wave mixing (FWM) scheme in asymmetric semiconductor quantum wells (SQWs) via two-photon resonance. By using the coupled Schrodinger–Maxwell formalism, we derive explicitly the corresponding analytical expressions of the inter-probe pulse and generated FWM field in the linear regime under the steady-state condition. With the aid of cross coupling between one ground state and two closely adjacent excited states, the efficiency of the generated FWM field is found to be significantly enhanced, up to 60%. More interestingly, a wide region of the maximum FWM efficiency is demonstrated as the ratio of transition dipole moments is within the values ranging from 1.1 to 1.3, which can be maintained for a certain propagation distance (i.e. 100 μm).

We investigate high-order harmonic generation in a metallic-nanoparticle–quantum-dot hybrid system. Driven by a moderate electric field intensity (1012 W/cm²) Guassian-shape few-cycle pulse which is chirped by a hyperbolic-tangent-form carrier envelope phase, the hybrid system can generate extreme-ultraviolet super-continuum harmonics (13.3 eV maximal photon energy) and isolated ultrashort pulses (3.03-4.7fs FWHM). Numerical simulation results reveal that the plasmonic field enhancement could extend the cutoff order and continuum region in harmonic spectra. The extension effect by plasmonic enhancement could be well understood theoretically by the semi-classical two-level atom model.

Tunneling-induced quantum interference experienced by an incident probe in the asymmetric double AlGaAs/GaAs quantum well (QW) structure can be modulated by means of an external control light beam and the tunable coupling strengths of resonant tunneling. These phenomena can be exploited to devise a novel intracavity medium to control Goos-Hänchen (GH) shifts of a mid-infrared probe beam incident on a cavity. For a suitably designed QW structure, our results show that maximum negative shift of 2.62 mm and positive shift of 0.56 mm are achievable for GH shifts in the reflected and transmitted light.

We propose and analyze an efficient way to enhance four-wave mixing (FWM) signals in a four-subband semiconductor quantum well via Fano-type interference. By using Schrödinger-Maxwell formalism, we derive explicitly analytical expressions for the input probe pulse and the generated FWM field in linear regime under the steady-state condition. With the aid of interference between two excited subbands tunneling to the common continuum, the efficiency to generate FWM field is found to be significantly enhanced, up to 35%. More interestingly, a linear growth rate in the FWM efficiency is demonstrated as the strength of Fano-type interference increases in presence of the continuum states, which can be maintained for a certain propagation distance (i.e., 50μm).

A scheme for generating the giant enhancement of the Kerr nonlinearity in a four-level system with the quantum coherences from the decays and the incoherent pumping is proposed. Compared with that generated in a general four-level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. By using the numerical results, we show that the remarkable enhancement should be attributed to the interaction of the quantum coherences from the decays and the incoherent pumping.

We study experimentally an electrically pumped GaAs-based bandgap structure based on a vertical cavity surface emitting laser (VCSEL). We demonstrate that a microcavity embedded into this bandgap VCSEL structure supports localized optical modes without any holding beam. We propose a model of surface-structured VCSELs based on a reduced dissipative wave equation for describing electromagnetic modes in such semiconductor cavities and analyze a crossover between linear and nonlinear solitonlike cavity modes.

By analyzing the nonlinear optical response in an asymmetric coupled double quantum well structure based on the intersubband transitions, we show that a giant Kerr nonlinearity with a relatively large cross-phase modulation coefficient can be used to produce efficient photonphoton entanglement and implement an all-optical two-qubit quantum polarization phase gate. We also demonstrate that such photon-photon entanglement is practically controllable and may facilitate more practical applications in all-optical quantum information and computation.