Electromagnetically Induced Transparency Peak Research Articles

Velocity selective multiple two-photon dark and bright resonances in Potassium vapor

We report the observation of two additional sub-natural line width quantum interferences in the D 2 manifold of 39 K vapor, in addition to the usual single Electromagnetically Induced Transparency (EIT) peak. In a typical three level Λ-type system, only one EIT peak is observed. However, here we report observation of two additional line shapes riding on top of the absorption profile. The fact that the hyperfine splitting is smaller than the Doppler width in 39 K allows the probe and control beams to swap their transition pathways in different velocity groups of atoms even when their frequencies are kept constant. Our observations are in striking contrast to standard EIT measurements. These findings are in quantitative agreement with density matrix formalism taking into account velocity-selective two-photon resonances. Owing to the favorably low ground hyperfine splitting (Δ hf ) in 39 K, which allows a significantly large number of atoms with a Doppler shift greater than or equal to the Δ hf , the strength of these additional resonances is strong compared to that of other alkali atoms such as 87 Rb, 133 Cs where these resonances can not be observed. The control photon detuning to atomic transition captures the nature of the coherence; therefore an unusual phenomenon of conversion from perfect transparency to enhanced absorption of the probe photon is observed and explained by utilizing the adiabatic elimination of the excited state in the Master equation. Controlling such dark and bright resonances leads to new applications in quantum technologies such as frequency-offset laser stabilization and long-lived quantum memory.

Accurate measurement of the frequency offset of the laser based on electromagnetically induced transparency

We propose a method using electromagnetically induced transparency (EIT) to measure the frequency offset of the laser relative to a cavity’s resonance frequency, thereby reducing the laser detuning when preparing Rydberg atoms. Laser reflection by the vapor cell enables observation of two EIT peaks corresponding to the co-propagating and counter-propagating beams, and the peaks’ position is related to laser detuning, allowing us to estimate the frequency offset of the probe and coupling lasers. The method reduces the measurement uncertainty compared to directly observing saturated absorption spectroscopy (SAS) and EIT, making it suitable for applications that require strict control over laser detuning.

Terahertz metal-graphene hybrid metamaterial for active manipulation of electromagnetically induced transparency

The dynamic tuning of terahertz (THz) electromagnetically induced transparency (EIT) offers significant potential in rapidly changing THz regulation fields, such as the next generation wireless communication, switching, and sensing. In this work, we demonstrate a THz EIT metamaterial by combining a circular and a rectangular split-ring resonator (CSRR and RSRR) based on the bright-bright mode coupling. The introduction of graphene into the EIT structure enables active tuning, and reveals two distinct regulation mechanisms in the metal-graphene hybrid EIT metamaterial: 1. the internal coupling effect diminishes with the increase of the Fermi level in the CSRR-graphene integration; 2. the surface electric field undergoes redistribution in the RSRR-graphene integration. These two dynamic regulation mechanisms are well confirmed by the simulated electric field distribution. As a result, the transmittance within the EIT window of the hybrid metamaterial can be precisely modulated, exhibiting a significant modulation depth of >85%. Notably, the integration with graphene in the RSRR allows for simultaneous modulation of resonances on either side of the EIT peaks, which expands more THz modulation channels. This work enriches the design and implementation methods for active THz EIT and shows potential applications in THz dynamic application scenarios.

Effect of neighboring transitions on the transformation between electromagnetically induced transparency and two-photon absorption

We report the effect of neighboring transitions on the transformation between electromagnetically induced transparency (EIT) and two-photon absorption (TPA) in an open multi-level ladder type system of 87Rb atom, the EIT peak exhibits split and asymmetric line feature owing to a neighboring transition line with a stronger relative hyperfine transition strength factor. By comparing the signals of the 5S1/2−5P3/2−5D3/2,5/2 transitions when increasing the power of the coupling laser, it can be found that avoiding neighboring effects due to Doppler broadening in a real atom, a lower decay rate of the excited state and a higher hyperfine transition strength ratio between the coupling and probe lasers are the crucial factors that enhance the transformation efficiency between TPA and EIT and the resolution of the switched spectra. Detailed theoretical calculations, considering the crucial factors, are consistent with the experimental results.

Study of microwave quantum electrometric sensors via electromagnetically induced transparency in thermal Rydberg atoms

Abstract Quantum electrometric sensing properties of a four-level system are theoretically investigated for microwave (MW) field measurement in thermal Rydberg atoms. In the considered system, the phenomenon of electromagnetically induced transparency (EIT) is invoked to study the impact of microwave (MW) field strength on its optical response. The amplitude of the MW electric field is obtained directly by measuring the height and frequency of EIT peaks. Further, for MW frequency measurement, the probe spectra are examined for red and blue MW detuned cases. It is found that the responsiveness of 133Cs for MW electric field as well as frequency is relatively higher than 87Rb. The overall sensitivity of both these atoms can be enhanced by the convenient setting of the system and field parameters.

Dual-band electromagnetically induced transparency terahertz metamaterial based on U-like resonator and metallic cut wire for sensing application

In this paper, a new scheme for dual-band terahertz electromagnetically induced transparency (EIT) is reported using a simple metamaterial structure, whose surface structure is composed of periodically arranged U-like resonator and metallic cut wire. Two EIT peaks located at 0.65 THz and 1.26 THz with an average transmission intensity of greater than 93% are realized, the formation mechanism of two transparent peaks is mainly attributed to the coupling of bright-bright mode, which is verified by their near-field distributions. Structure parameter changes of metamaterial provide a great ability to regulate and control the performance of two transparent peaks. Interestingly, by replacing the lower baseline of U-like resonator with vanadium dioxide (VO2), the designed metamaterial can dynamically tune the number of EIT peaks. It is revealed that dual-band transparency could be actively converted to single-band transparency by merely varying the properties of VO2 from metallic state to insulating state without changing the structure complexity, and the maximum amplitude modulation depth could reach 93.1%. Further application of designed metamaterial related to sensing is discussed. The designed metamaterial with these excellent features could pave the way for the applications of terahertz technology-related fields.

Interplay of polarizations in a cascade EIT system in the presence of vortex coupling light in 87Rb atomic vapor medium

We investigate both experimentally and theoretically the cascade electromagnetically induced transparency (EIT) in configuration in 87Rb atomic vapor medium in the presence of vortex coupling Laguerre Gaussian (LG) light. We demonstrated Doppler free double resonance EIT structure in cascade configuration and observed transmission spectra for and polarized probe and coupling lights. We demonstrate that the double resonance structure can be identified by two photon transition probabilities and it is found to be and . By considering coupling LG light, several polarization combinations are taken into account, and their effects on amplifying and diminishing the EIT resonances are demonstrated experimentally. In order to understand the polarization effects of vortex coupling light on EIT spectrum in a degenerate multilevel atomic system, a theoretical model is developed by considering a simplified double hut level structure. Semi-classical density matrix analysis is used to understand the dynamics and also to establish the enhancement and reduction of EIT peak height with coupling light polarizations. The impact of two photon transition probabilities, polarization combinations and relative orientations of probe and coupling lights in degenerate multilevel atomic systems leads to modification of EIT resonances significantly. We establish quantitative agreement between our theory and experimental results.

Optical pumping effects on high-contrast Rydberg electromagnetically induced transparency

We discuss the interplay between high-contrast Rydberg-state electromagnetically induced transparency (EIT) and optical pumping (OP) in a thermal 87Rb medium. By pumping the population to one single hyperfine state, we can enhance the interaction strength and, in principle, amplify the EIT peak. According to the measurements, the EIT peak height can be improved by a factor of two or reduced by one order of magnitude, and linewidth was slightly narrowed by the pumping effect. The EIT feature is predicted quantitatively using a Doppler-free non-perturbation numerical calculation. In both simulations and measurements, Rydberg-EIT enhancement through OP is dependent on the intensity of the probe field and the optical density. Our work clarifies the underlying mechanisms of optical pumping, making relevant studies useful in developing Rydberg-based electrometry.

Atom-based power-frequency electric field measurement using the radio-frequency-modulated Rydberg spectroscopy

The radio-frequency modulated electromagnetically induced transparency (EIT) in a ladder three-level system with Rydberg state is studied. Under the influence of a fast radio-frequency field, the EIT peak splits into a series of sidebands. When attaching a power-frequency electric field directly to the fast radio-frequency field, the odd-order sidebands of the Rydberg-EIT oscillate sensitively with the power-frequency field. The oscillation frequency is equal to twice the power frequency; the oscillation amplitude is monotonically increasing with the amplitude of the power-frequency field when the change of Stark-shift is smaller than the radio frequency. Our work paves the way for measurement of power-frequency electric field based on Rydberg atoms.

All-dielectric Si metamaterials with electromagnetically induced transparency and strong gap-mode electric field enhancement

We designed all-dielectric π-shaped Si metamaterials and numerically demonstrated their electromagnetically induced transparency (EIT) behavior. Each unit of the metamaterial comprises one horizontal Si nanobar and two vertical Si nanobars with feed-nanogaps between them. A narrow EIT peak with a transmittance of 99% and a Q-factor of 2436 is observed due to the destructive interference between the horizontal bright and vertical dark mode resonators. The EIT can be tunable by changing the nanogap width, and the narrowest EIT window with the largest Q-factor is obtained as the nanogap width is 20 nm. Strong electric field enhancement exceeding 104 in magnitude is also realized inside the 20-nm nanogap. Theoretical fittings according to the coupled Lorentz oscillator model exhibit a well consistency with the simulation spectra, validating the accuracy of the numerical simulation. The designed metamaterial is sensitive to the surround refractive index change with a figure-of-merit of 460, which far exceeds Fano-resonant plasmonic metal sensors. The designed Si metamaterial with a sharp EIT response and a strong electric field enhancement is an ideal platform for applications in optical sensing, low-loss slow-light devices, fluorescence enhancement, and nonlinear optics.

Polarization multiplexed electromagnetically induced transparency metasurface based on VO2 with high-performance sensing application

A vanadium dioxide (VO2) based dielectric metasurface is proposed to realize polarization multiplexed electromagnetically induced transparency (EIT) effect with tunability. In the near-infrared regime, distinct transparency windows with high transmission intensity and quality factor (Q-factor) can be observed under the excitation of two orthogonal polarized lights. By changing the conductivity of VO2, the EIT peak intensity and the group delay of the incident light can be manipulated dynamically. Meanwhile, the narrow transparency window is extremely sensitive to the change of the surrounding refractive index, and the proposed metasurface exhibits high sensitivity and figure of merits in both x- and y-polarization conditions. Therefore, the proposed dielectric metasurface based on VO2 provides a new method for dynamically controlled EIT effects in the near-infrared region and inspires potential applications in optical modulations, tunable slow light devices, and high-performance refractive index sensors, etc.

Observation of V-type electromagnetically induced transparency and optical switch in cold Cs atoms by using nanofiber optical lattice

Optical nanofiber (ONF) is a special tool to achieve the interaction between light and matter with ultralow power. In this paper, we demonstrate V-type electromagnetically induced transparency (EIT) in cold atoms trapped by an ONF-based two-color optical lattice. At an optical depth of 7.35, 90% transmission can be achieved by only 7.7 pW coupling power. The EIT peak and linewidth are investigated as a function of the coupling optical power. By modulating the pW-level control beam of the ONF-EIT system in sequence, we further achieve efficient and high contrast control of the probe transmission, as well as its potential application in the field of quantum communication and quantum information science by using one-dimensional atomic chains.

Optimizing the Rydberg EIT spectrum in a thermal vapor.

We present Rydberg-state electromagnetically-induced-transparency (EIT) measurements examining the effects of laser polarization, magnetic fields, laser intensities, and the optical density of the thermal 87Rb medium. Two counter-propagating laser beams with wavelengths of 480 nm and 780 nm were employed to sweep the spectrum across the Rydberg states |33D3/2〉 and |33D5/2〉. An analytic transmission expression well fits the Rydberg-EIT spectra with multiple transitions under different magnetic fields and laser polarization after accounting for the relevant Clebsch-Gordan coefficients, Zeeman splittings, and Doppler shifts. In addition, the high-contrast Rydberg EIT can be optimized with the probe laser intensity and optical density. Rydberg EIT peak height was achieved at 13%, which is more than twice as high as the maximum peak height at room temperature. A quantitative theoretical model is employed to represent the spectra properties and to predict well the optimization conditions. A Rydberg EIT spectrum with high contrast in real time can be served as a quantum sensor to detect the electromagnetic field within an environment.

Active modulation of electromagnetically induced transparency analog in graphene-based microwave metamaterial

Metamaterial analogs of electromagnetically induced transparency (EIT) enable a unique route to enhance light-matter interactions without quantum approach, showing remarkable potentials for slow-light devices and highly sensitive sensors. In particular, dynamic control of EIT in metamaterials opens new avenues for optical networks and electromagnetic communications. Here, we experimentally present, for the first time, the active modulation of EIT analog by integrating graphene into a microwave metamaterial. Experimental results demonstrate that the EIT peak can be dynamically controlled under a relatively low bias voltage applied on graphene. A coupled harmonic oscillation model is exploited to analyze the physical mechanism which lies in the active tuning of the damping rate of the dark mode resonator through varying the graphene's sheet resistance. Via variably dampening the dark resonator using graphene, the coupling condition could be electrically modulated and the continuous tuning of the EIT resonance strength is achieved. In addition, the controllable slow-wave propagation is also performed theoretically based on the tunable phase delay of the transmitted waves. This work opens up promising possibilities for slow-wave manipulation with applications in smart and multifunctional devices.

Bidirectional Electromagnetically Induced Transparency Based on Coupling of Magnetic Dipole Modes in Amorphous Silicon Metasurface.

A bidirectional electromagnetically induced transparency (EIT) arising from coupling of magnetic dipole modes is demonstrated numerically and experimentally based on nanoscale a-Si cuboid-bar metasurface. Analyzed by the finite-difference time-domain (FDTD) Solutions, both the bright and dark magnetic dipole mode is excited in the cuboid, while only the dark magnetic dipole mode is excited in the bar. By breaking the symmetry of the cuboid-bar structure, the destructive interference between bright and dark magnetic dipole modes is induced, resulting in the bidirectional EIT phenomenon. The position and amplitude of simulated EIT peak is adjusted by the vertical spacing and horizontal spacing. The EIT metasurface was fabricated by Electron-Beam Lithography and deep silicon etching technique on the a-Si film deposited by Plasma-Enhanced Chemical Vapor Deposition. Measured by a convergent spectrometer, the fabricated sample achieved a bidirectional EIT peak with transmission up to 65% and 63% under forward and backward incidence, respectively. Due to the enhanced magnetic field induced by the magnetic dipole resonance, the fabricated bidirectional EIT metasurface provides a potential way for magnetic sensing and magnetic nonlinearity.

Terahertz hybrid metal-graphene metamaterials with tunable dual-band electromagnetically induced transparency

The electromagnetically induced transparency (EIT) effects in metamaterials have been widely studied due to their broad application prospects in the field of optical communications. Previous researchers focused mainly on the regulation of a single EIT effect. Here we proposed a structure containing two pairs of asymmetric C-shaped double-split ring resonators (DSRRs) placed on the two sides of cut wire (CW), and we studied the EIT effect of the structure. Furthermore, in order to tune the EIT peak, two graphene strips are placed on the two pairs of DSRRs. Simulation results show that, the EIT peak can be modulated by adjusting the Fermi level of the graphene strips and the modulation depths as high as 83 % and 87 % can be realized. Besides, slow light phenomenon accompanied by the EIT effect in the structure was investigated. Simulation results implied that, double group delays of 4.4 ps and 3.4 ps can be achieved in the design, and the delays can be adjusted by changing the graphene Fermi level. The physical mechanism of the tunable metamaterial was analyzed in terms of the three-oscillator model.

Actively tunable and switchable electromagnetically induced transparency in hybrid metal-graphene metamaterials

Active control of the electromagnetically induced transparency (EIT) is highly desirable for advanced terahertz (THz) device applications. Currently, the EIT peak positions in the graphene-based metamaterials have been actively controlled by tailoring Fermi energy of graphene via electric doping. However, there is still a considerable challenge to realize active strength modulation of the EIT peak without frequency shifting. Here, a hybrid metal-graphene structure, consisting of the metal-based EIT metamaterial and patterning graphenes, is proposed at the THz frequencies. Through changing Fermi energy of graphene, the EIT peak strength can exhibit both active modulation and on-to-off switch without frequency shifting. Moreover, theoretical model and field distributions discover that the active response can be attributed to the increasing damping rate of the dark mode caused by the controllable conductivity of graphene. In addition, the controllable group delay is also achieved for the slow light applications. Therefore, this work provides the possibility for designing compact slow light devices in the information processing and telecommunication applications.

Effects of vector magnetic field on electromagnetically induced transparency with lin ⊥ lin polarization

The effect of a vector magnetic field was studied on electromagnetically induced transparency (EIT) with linear ⊥ linear polarization of the probe and pump beams in 87 R b − D 2 transition with a vapor cell at room temperature. The dependence of EIT on the direction of the quantization axis and the relative orientation of the polarizations of the applied electric fields was studied experimentally. We show that from the relative strengths of σ and π EITs, the direction of the magnetic field can be found. Moreover, from the relative separation between σ and π EITs, the strength of the magnetic field can be calculated. We also demonstrate that the EIT peak amplitudes show oscillatory behavior depending upon the orientation of the laser polarization relative to the magnetic field direction. To understand the experimental observations, a theoretical study was done numerically considering all 13 Zeeman sub-levels. Apart from the numerical simulation, a toy model was also constructed to obtain an analytical response of the medium considering the velocity distribution. The dependencies of the magnetic field direction and polarization direction of the electric field were explicitly derived with the analytical model.

Measurement of multi-frequency dispersions of Electromagnetically Induced Transparency windows using Spatial Light Modulator in rubidium vapor

In this letter, we have measured the dispersive profile of the multi window Electromagnetically Induced Transparency(EIT) signals in Rubidium (Rb) atomic medium at room temperature. Weak probe laser light and strong coupling light in counter propagating direction are used to excite the atomic medium via ladder type configuration of87Rb D2 line to obtain multiple EIT peaks. The uniqueness of our work is in the experimental setup which is used for the measurement of dispersion. We have used transmissive Spatial Light Modulator(SLM) in one arm of the Mach–Zehnder(M–Z) interferometer to obtain the desired phase shift between two interfering arms for the measurement of dispersive properties of multi window EIT in Rb vapor medium. One can easily obtain the phase shift without disturbing the alignment of the M-Z interferometer by using this setup.

Active EIT-like Dependent on Polarization Angle with Graphene Metamaterial

An active electromagnetically induced transparency (EIT) analog adopting graphene as microstructure of metamaterial is investigated. The analog consist interconnected graphene strip (GS) and graphene split ring resonator (GSRR), which can act as bright and dark elements alternately. The distinct EIT-like effect can be generated by bright-dark mode coupling in x and y polarization directions. Further investigations reveal that EIT peak can be actively controlled via Fermi level of graphene, and theoretical analysis based on two particles mode express the reason. Moreover, notable EIT-like effect can also be generated in a wide range of polarization angles, and impact of polarization angle on EIT peak is also discussed in detail. These characteristic paves the way for the applications of EIT-like in sensor device.