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In this paper, toroidal localized spoof surface plasmons (LSSPs) based on homolateral double-split ring resonators is proposed and experimentally demonstrated at microwave frequencies. By introducing a new split in the conventional single-split ring resonator, the magnetic field in resonator is locally modified. The double-split ring resonator can create the mixed coupling in the structure, leading to the enhancement of magnetic field. Both numerical simulations and experiments are in good agreement. Compared with traditional toroidal LSSPs based on the single-split ring resonators, the imperfection of toroidal LSSPs is resolved, the intensity of toroidal resonance and the figure of merit (FoM) are significantly enhanced. To understand and clarify the enhanced magnetic field phenomena, we analyze the role of the double-split ring resonator. The effect of location of source and spacing between two splits on the resonance intensity are also discussed. A higher intensity of toroidal LSSPs resonance could be achieved by changing the spacing between two splits. Additionally, it is experimentally demonstrated that the enhanced toroidal LSSPs resonance is sensitivity to the background medium. The results of our research provide a new idea for exciting the enhanced toroidal dipole.

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.

In this Letter, numerical and experimental studies for the spoof-anapole effect are presented. Different from the anapole modes, when electric and toroidal dipole intensities are minimized, the spoof-anapole effect can be generated. The spoof-anapole effect can reduce the radiation losses with a high Q -factor. The concept is valid in various frequency bands from microwave range for millimeter-sized objects to visible range for nanoparticles. The spoof-anapole modes are first experimentally realized in microwave metamaterials. Almost perfect spoof-anapole behavior is observed, which produces an extremely high Q -factor at the resonance frequency. The experimental results agree well with the analytical ones and pave way to excite the non-radiating electromagnetic sources.

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 an effective scheme for high-precision three dimensional(3D) atom localization via measuring the population of excited state in a four-level atomic system driven by a probe field and three orthogonal standing-wave fields. In this scheme, the position-dependent multiphoton quantum destructive interference leads to multiphoton excitation of the excited state and enhances the fluorescence emission. We show that adjusting the frequency detuning and phase shifts associated with the standing-wave fields can modify the multiphoton quantum destructive interference and lead to a redistribution of the atoms. The maximal probability of finding the atom at the certain position in one period of the standing-wave fields can be 100% and the highest spatial precision is about 0.02λ.

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.

The properties of two and three two-split-ring-resonators (TSRRs) are investigated in this paper, which shows a remarkable Fano resonance in the microwave frequency. In two TSRRs, the Fano resonance results from the interference between two TSRRs by conductive coupling, both experiments and numerical simulations are in good agreement. The structure shows strong magnetic dipole at the intersection of two TSRRs. In three TSRRs, the double Fano resonances can be excited and double magnetic dipoles produce at two intersections. Because of the interaction between two magnetic dipole, symmetric magnetic dipole and anti-symmetric magnetic dipole (toroidal dipole) modes are presented, respectively. An almost doubled Q factor is observed in the three TSRRs compared to the two TSRRs. In addition, we experimentally demonstrate that the double Fano resonances are sensitivity to the refractive index of background. The sensitivity changes with the change of position of detected material. The highly sensitive areas of double Fano resonances locate at two intersections. This study paves the way to excite the multiple Fano resonances. Such Fano resonance can be applied to the sensors.

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 a theoretical scheme to coherently control the transport of a single electron in an asymmetric double-quantum-dot system. The single-electron transport originates from the intrinsic interplay between the externally applied few-cycle pulse and the inter-dot tunneling. Solving the equations of motion for dot-density matrix, we reveal numerically that the current exhibits a significant dependence on the carrier-envelope phase (CEP) of the few-cycle pulse, which is similar to the magnetic flux controlled coherent transport in an Aharnov–Bohm (AB) interferometer. As a result, by varying the CEP of the pulse one can suppress or enhance the current either instantaneously or periodically. Our results illustrate the potential to utilize few-cycle pulses for excitation in quantum dot systems through the CEP control, as well as a guidance in the design for possible experimental implementations.

We analyze the absorption-dispersive properties of a weak probe laser field based on the ISBT in a triple semiconductor quantum well (SQW) structure driven coherently by two control laser fields. It is shown that the system can produce anomalous and normal dispersion regions with negligible absorption by adjusting the intensities of the control fields and the Fano-type interference. More interestingly, the dispersion can be changed between normal and anomalous simply by adjusting the relative phase between two coherent control fields due to the existence of the Fano-type interference. Thus the relative phase can be regarded as a switch to manipulate light propagation with subluminal or superluminal. In addition, the temporal and spatial dynamics of the probe laser pulse with Gaussian-type envelope are analyzed.

The visibility of ghost-interference patterns is investigated firstly based on the coherent-mode representation theory. We find that the intensity correlation function can be changed from the usually two-dimensional integral representation to a new one-dimensional summation representation. During the process of analyzing the effects from the light source's properties and the transmission area of the object imaged on the imaging visibility, it is shown that by compared with the results from the integral representation, the coherent mode representation is quite useful to understand more clearly the whole process of correlated imaging.

We investigate the effects of geometrical and structural disorders on perfectly asymmetric diffraction (PAD) in Raman-Nath regime. The two types of disorders are realized by introducing random fluctuations in the position and width of one-dimensional (1D) driven atomic lattices. Raman-Nath diffraction is modified differently with respect to the geometrical and structural disorders. It is shown that the PAD is observed with a certain strength range of geometrical disorder, exceeding which it can be destroyed, while the PAD is rather robust against structural disorder. The different behaviors originate from the disorder-induced random variations of the spatial phase shifts of the standing-wave (SW) coupling field and atomic lattices with Gaussian profile. Furthermore, we find that, in the presence of geometrical disorder, the PAD is more susceptible to correlated disorder than to uncorrelated disorder. Our scheme may be useful for understanding the effects of disorder on the diffraction of light and matter waves in disordered potentials..

Here, on a platform of two split-ring resonator (SRR) disks in the microwave regime, we have numerically and experimentally investigated the coupling of toroidal localized spoof surface plasmons (LSSPs). The coupling effect is investigated both theoretically and experimentally. We observe that magnetic dipole coupling exists in the toroidal LSSPs coupling and causes a rearrangement of the toroidal LSSPs, which suppresses the propagation of toroidal LSSPs. To realize the propagation of toroidal LSSPs, we introduce conductive coupling into the SRR disks. The conductive coupling can correct magnetic dipole coupling and enhance toroidal LSSPs coupling. Both numerical simulations and experiments are in good agreement. The toroidal LSSPs can be effectively propagated, even in the three right-angle-bent SRR disks. This study paves the way toward a better understanding of toroidal LSSPs coupling and finds many applications in the transfer of electromagnetic energy using toroidal moments.

The theoretical analysis of the noise property is presented in a correlated imaging system. For both entangled source produced by parametric down-conversion (PDC) and classically light source, a small aperture of the imaging system makes the noise increase slightly and the resolution of the imaging signal degrade. We also show that, in PDC case, the noise is strongly influenced by the source size because of the existence of the entanglement, while the effect is not obvious in the thermal case.

We investigate two imaging schemes, lensless system and 2-f system which are used to implement ghost diffraction. It is shown that the two schemes have similar intensity fluctuation correlation functions which both realize the function of the Fourier-transform imaging, and the diffraction pattern is in agreement with that in the classical wave optics. The difference of the imaging visibility in the two systems is also discussed.

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 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.

We propose and analyze an effective scheme to generate hyper-Raman scattering via inhibiting electromagnetically induced transparency (EIT) in a monolayer graphene under a magnetic field. By solving the Schrödinger-Maxwell formalism, we derive explicitly analytical expressions for linear susceptibility, nonlinear susceptibility, and generated Raman electric field under the steady-state condition. Based on dressed-state theory, our results show a competition between EIT and hyper-Raman scattering, and the hyper-Raman process is totally dominant when multiphoton destructive interference is completely suppressed.

A scheme of enhanced Goos-Hanchen (GH) shifts in reflected and transmitted light beams is exploited in a cavity, where an asymmetric double AlGaAs/GaAs quantum well structure with resonant tunneling to a common continuum is employed as the intracavity medium. With the help of Fano-type interference induced by resonant tunneling, the generated GH shifts that contain a negative lateral shift in reflected light beam and a positive lateral shift in transmitted light beam are found to be significantly enhanced. More interestingly, these GH shifts in reflected and transmitted light beams are modulated by means of a control beam and external bias voltage, in which maximum negative shift of 1.86 mm and positive shift of 0.37 mm are achievable.

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.

By analyzing the interaction of a few-cycle laser pulse within an asymmetric semiconductor double quantum well structure, we show that the transient coherence thus produced is strongly dependent on the carrier-envelope-phase (CEP) and significantly enhanced due to the Fano-type interference. A method to determine the CEP is proposed by directly mapping the CEP dependent coherence to the quantum beat signals.

A new scheme of five-level hyper V-type atomic system is proposed with the aim of generating slow temporal vector optical solitons. Two transitions in the five-level atomic medium independently interact with the two orthogonally polarized components of a low intensity linear-polarized pulsed probe field, while two other transitions are driven by control laser fields. We demonstrate that various distortion-free slow temporal vector optical solitons, such as bright-bright, bright-dark, dark-bright and dark-dark vector solitons, can be evolved from the probe field. Besides, we also show that the modified Hubbard model that includes the Manakov system may be realized by adjusting the corresponding self- (cross-) phase modulation and dispersion effects of this system.

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 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).

We conducted a theoretical investigation of the optical steady-state behavior in N four-level Y-type atoms driven coherently by a probe laser and a single elliptically polarized field (EPF) by means of a unidirectional ring cavity. It was found that the optical bistability can be observed for a wide regime of frequency detuning of the probe field, intensity of the EPF, and the atomic cooperation parameter. Interestingly, in principle the optical steady-state behavior can be switched from optical bistability to multistability or vice versa by adjusting the phase difference between two components of the polarized electric field of the EPF if the perfect spontaneously generated coherence of atoms is included. Our results illustrate the potential to utilize EPF for all-optical switching in atomic systems through the phase control, as well as provide guidance in the design for possible experimental implementations.

We analyze the hybrid absorptive-dispersive optical bistability (OB) behavior in an open Λ-type three-level atomic system by using a microwave field to drive the hyperfine transition between two lower states, along with the consideration of incoherent pumping and spontaneously generated coherence. Different from the closed system, we show that the bistable threshold intensity and related hysteresis loop can be controlled by adjusting the ratio between atomic injection and exit rates. More interestingly, the appearance and disappearance of OB can be transformed mutually by varying the relative phase of three coherent fields under the condition of a strong spontaneously generated coherence. The manipulation of OB behavior through the intensity of the microwave field and the atomic cooperation parameter is also analyzed.

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.

We show the possibility of generating ultraslow temporal vector optical solitons in a cold lifetime-broadened four-level tripod atomic medium under Raman excitation. We demonstrate that the two orthogonally polarized components of the low-intensity signal field can evolve into various distortion-free temporal vector optical solitons, such as bright-bright vector solitons with ultraslow group velocity. These results are produced from the balance of self- and cross-phase modulation effects and dispersion. We also show that Manakov temporal vector solitons may be realized by adjusting the corresponding self- and cross-phase modulation and dispersion effects of our system.