Electromagnetically Induced Transparency Research Articles

Measurement of relative transition strengths of 133Cs Rydberg D states using electromagnetically induced transparency

Transition strengths between states are fundamental physical properties of atomic spectra. The differences in fine structure splitting of certain states are mainly attributed to the angular momentum parts of transition dipole matrix elements. These can be calculated by integrating the wave-functions theoretically and can be accessed by selecting corresponding polarizations of the exciting lasers experimentally. We measured the transition strengths ratios of nD5/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{5/2}$$\\end{document}/nD3/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3/2}$$\\end{document} via Rydberg electromagnetically induced transparency (EIT) by changing the powers and polarizations of probing and coupling lasers in a room temperature cesium vapor cell. The variation of the ratios on the principal quantum number n which ranges from 40 to 62 is also investigated. Theoretical and experimental results agreed with each other.

Optical switch based on tunable perfect photon absorption

We investigate the manipulation of optical field within quantum electrodynamics (QED) scheme. In our proposal, the cold three-level atoms interact with a two-sided cavity driven by two coherent beams with a relative phase. Coherent perfect absorption (CPA) appears when the beams are in phase. However, the perfect outputs occur when the beams are out of phase. On the basis of the phase modulation, an optical switch can be operated at a high efficiency. With a coherent control laser, the excited and metastable levels of the atoms are coupled. Electromagnetically induced transparency (EIT) is produced at two-photon resonance, which leads to four-band CPA. By virtue of the control laser, the switching efficiency can be maximized in a weaker probe field, which provides advantages over two-level atoms on weak-signal switching.

Multi-band tunable electromagnetically induced transparencies based on active metasurface with polarization-independent property

The analogue of an electromagnetically induced transparency (EIT) spectrum is achieved using a metasurface that consists of an array of cross and L-shaped resonators. The mechanism of the EIT-like phenomenon are analyzed, and the influence of geometrical parameters on the effect is discussed. We achieve a multi-band EIT-like through structure configuration. In particular, polarization-independent EIT is realized. A potential application in sensing is suggested and the sensitivity of 65 GHz RIU−1 is obtained. We also investigate the impact of analyte and substrate on the transmission spectrum. We find that when the analyte thickness is higher than 40 μm, the EIT spectral shift is less affected by the analyte thickness. The thickness insensitive characteristics are beneficial for reducing errors caused by analyte dose, thereby improving the accuracy of sensing. By introducing a phase change material, vanadium dioxide, we obtain active control of the EIT effect. Our results provide valuable insights into the development of multi-band tunable compact devices based on metasurfaces.

Two-photon coherence in a DROP-FWM medium

In this work, we report experimental studies on coherence in a medium exhibiting DROP (Double Resonance Optical Pumping)-FWM (Four Wave Mixing). Here 5S1/2(F) → 5P3/2(F/) → 5D (F//) two photon transition of hot 87Rb atoms is used. The 5S→5P connection is modified by introducing an additional beam phase coupled to the original beam linking F = 2 → F/ transition. The frequency of the additional beam is offset from that of the original beam by ≈ +10Γ (Γ is natural linewidth). Such a two-beam configuration in F→F/ manifold effectively satisfies conditions of Vee (V) linkage or degenerate two-level connection (DTLC), depending on the detuning of the 780nm laser. This transformation profoundly affects the behavior of the ensuing Ladder (Ξ) system. While the (I) Ξ +V condition is favorable for Electromagnetically Induced Transparency (EIT), the (ii) Ξ + DTLC brings in the effect of Electromagnetically Induced Absorption (EIA). The EIT-dominated situation is helpful for FWM to take place, and the EIA effect augments the stronger presence of DROP. This condition is verified by monitoring the blue fluorescence emanating from the 5D→6P3/2→5S1/2 decay route. The DROP effect follows the Amplified Spontaneous Emission (ASE) pattern in the media. The origin of blue photons is also due to FWM under EIT conditions. In the case of EIA, the dominant condition increment in blue fluorescence is due to increased stimulated emission. The blue photons mainly contributed by (i) FWM and (ii) increased participation of stimulated emission are directional in nature and phase coherent.

Ultra-high-Q free-space coupling to microtoroid resonators

Whispering gallery mode (WGM) microtoroid resonators are one of the most sensitive biochemical sensors in existence, capable of detecting single molecules. The main barrier for translating these devices out of the laboratory is that light is evanescently coupled into these devices though a tapered optical fiber. This hinders translation of these devices as the taper is fragile, suffers from mechanical vibration, and requires precise positioning. Here, we eliminate the need for an optical fiber by coupling light into and out from a toroid via free-space coupling and monitoring the scattered resonant light. A single long working distance objective lens combined with a digital micromirror device (DMD) was used for light injection, scattered light collection, and imaging. We obtain Q-factors as high as 1.6×108\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.6\ imes {10}^{8}$$\\end{document} with this approach. Electromagnetically induced transparency (EIT)-like and Fano resonances were observed in a single cavity due to indirect coupling in free space. This enables improved sensing sensitivity. The large effective coupling area (~10 μm in diameter for numerical aperture = 0.14) removes the need for precise positioning. Sensing performance was verified by combining the system with the frequency locked whispering evanescent resonator (FLOWER) approach to perform temperature sensing experiments. A thermal nonlinear optical effect was examined by tracking the resonance through FLOWER while adjusting the input power. We believe that this work will be a foundation for expanding the implementation of WGM microtoroid resonators to real-world applications.

Terahertz structured deep-subwavelength plasmonic grating metasurface for manipulating polarization-dependent coupling response

The complex electromagnetic anisotropy of terahertz (THz) metasurfaces with geometric symmetry breaking has attracted extensive attention. Typical effects arise from the coupling of polarization responses in orthogonal directions of various components of the metasurface structure, such as the electromagnetically induced transparency (EIT) effect. However, it is a challenge to precisely control or perfectly avoid the polarization-dependent coupling responses. In this work, deep-subwavelength plasmonic gratings (PGs) with a fine wire width of 1 μm at the order of deep subwavelengths of 1/100 THz wave are fabricated by electron beam lithography, and these wire gratings are graphically designed as a C-shaped metasurface pattern with a period of 100 μm in sub-wavelength scale. The complete anisotropic response in the single-oriented PG metasurface is demonstrated by both simulation and experiments, where the polarization-dependent coupling effect is eliminated. More interestingly, the hybrid-oriented PG metasurface exhibits narrowband and wideband EIT effects in the x and y polarization directions with the maximum polarization extinction ratio of 20 dB, respectively, indicating this mechanism can realize more flexible manipulation of polarization-dependent coupling. This patterned deep-subwavelength PG provides a new structure and mechanism for excitation, regulation, and restriction of polarization-dependent mode coupling, and has important applications in THz spectroscopic detection, polarization imaging, and wireless communication.

Electromagnetically induced transparency and quantum enhancement of transmission via dressed bloch photons in an array of three-level Λ-type atoms.

We investigate the interactions between an array of three-level atoms and two photon fields with distinct frequencies employing quantum electrodynamics (QED). The control beam, as expected, has a considerably higher intensity than the probe beam, and the probe photon's eigenstate notably then appears as a distinctive dressed Bloch wave. We calculate the dispersion relation and quantum amplitude of the probe photons for their transmission. At positions predicting electromagnetically induced transparency (EIT) phenomena, we unveil remarkable enhancements in the transmission of the probe beam. Crucially, these enhancements are intricately linked to the unique characteristics of the dressed Bloch wave eigenstate. Moreover, we demonstrate that modulating frequency and intensity of the control beam and the lattice constant would further tune these enhancements. Our study highlights the crucial role of the dressed Bloch wave eigenstate in substantially amplifying targeted light beams, thereby significantly enhancing the detection sensitivity for minute electromagnetic signals and emphasizing its pivotal role in unveiling intriguing phenomena.

Tunable C4-Symmetry-Broken Metasurfaces Based on Phase Transition of Vanadium Dioxide (VO2).

Coupling is a ubiquitous phenomenon observed in various systems, which profoundly alters the original oscillation state of resonant systems and leads to the unique optical properties of metasurfaces. In this study, we introduce a terahertz (THz) tunable coupling metasurface characterized by a four-fold rotation (C4) symmetry-breaking structural array achieved through the incorporation of vanadium dioxide (VO2). This disruption of the C4 symmetry results in dynamically controlled electromagnetic interactions and couplings between excitation modes. The coupling between new resonant modes modifies the peak of electromagnetic-induced transparency (EIT) within the C4 symmetric metasurfaces, simulating the mutual interference process between modes. Additionally, breaking the C4 symmetry enhances the mirror asymmetry, and imparts distinct chiral properties in the far-field during the experimental process. This research demonstrates promising applications in diverse fields, including biological monitoring, light modulation, sensing, and nonlinear enhancement.

Versatile terahertz metasurface: dynamic switching between electromagnetically induced transparency and perfect absorption

This paper introduces a versatile metasurface based on vanadium dioxide (VO2) and graphene that seamlessly transitions between electromagnetically induced transparency (EIT) and multi-band absorption through VO2’s phase change property. When VO2 is in a dielectric state, the device can generate EIT. This configuration allows dynamic tuning of the central frequency by adjusting the graphene’s Fermi levels (E f ), achieving a remarkable group delay of 1.42 ps. When VO2 is in a metallic state, the structure facilitates a Fabry–Perot resonance between the VO2 layer at the bottom and the graphene layer at the top, leading to exceptional light absorption. Specifically, absorptivity of 99.8% and 99.4% is achieved at 1.66 THz and 2.87 THz, respectively. In addition, these two resonance peaks can also be dynamically adjusted by modulating E f . Furthermore, the device serves as a highly sensitive sensor with sensitivity up to 0.65 THz/RIU. Notably, both absorption and EIT modes are polarization-insensitive and exhibit tolerance to a wide range of incidence angles. Consequently, the proposed device holds significant promise across various applications within the electromagnetic field, including tunable devices, absorbers, sensors, slow-light devices, and so on.

Azimuthal phase-dependent electromagnetically induced transparency and the generation of spatial light in a microwave-assisted four-level Y-type system

We present an azimuthal phase-dependent scheme to study the spatially dependent electromagnetically induced transparency (EIT) and the generation of spatial light in a closed-loop four-level Y-type system. A structured control beam and a microwave (MW) field are adopted in the closed-loop structure. Interestingly, the weak non-vortex probe beam responses explicitly depend on the orbital angular momentum (OAM) of the control beam along with the MW-assisted quantum interference. The regions of spatially dependent EIT are demonstrated at different azimuthal angles. It is found that the intensity of the structured control beam and the relative phase arising out of the beams participating in the closed-loop can be used as the controlling knobs to tailor the shape and the angular location of the spatially dependent EIT.

Phase-sensitive large Kerr nonlinearity in semiconductor quantum wells

This paper presents a comprehensive investigation on Kerr nonlinearity in a three-level semiconductor quantum well (SQW) superlattice and validates the existence of large Kerr nonlinearity of the order of [Formula: see text] in the vicinity of an electromagnetically induced transparency (EIT) window. The Kerr nonlinearity is found to vary with the relative phase of the applied optical fields, and by selecting suitable relative phases, an enhanced Kerr nonlinearity can be obtained. The results may find significant applications in optoelectronic and photonic devices.

Triple-band graphene-based tunable electromagnetically induced transparency terahertz metamaterial with multi-frequency optical switching

A simple graphene-based terahertz metamaterial with the composite patterns of a π-shaped and a strip-shaped is proposed for realizing the electromagnetically induced transparency (EIT) effect. Three efficient transparent peaks with the average transparency strength of >85 % are achieved. The physical mechanism of the formation of the triple-band EIT effect is illustrated by the transmission spectra combined with the electric field diagrams of the transparent window and the transmission dip. Interestingly, upon changing the position of the strip-shape graphene and the distance between the vertical graphene, the triple-band EIT effect shifts to a dual-band and a single-band, respectively, illustrating the reason for the shifts using the electric field of peaks and dips. The Fermi energy level of graphene can be changed by biasing voltage to create a frequency shift of the resonance peaks of the transmission spectrum, and at the same time, six-frequency optical switching can be realized, which has a modulation degree of amplitude (MDA) of 94.6 %, 90.6 %, 98.1 %, 90.5 %, 97.6 %, and 89.4 %, respectively. These results indicate that the proposed multi-band terahertz metamaterials have great potential for applications in fields such as optical switching and sensing.

Triple electromagnetically induced transparency generated slow light for multiple carbon nanotube resonators

Hybrid spin-mechanical systems offer a promising platform for advancing quantum science and technology. However, practical implementation of applications within these hybrid quantum systems demands the seamless integration of supplementary physical components. In this context, we present a proposal for a multi-mode spin-mechanical setup, featuring the utilization of three-mode coupling nanomechanical carbon nanotube (CNT) resonators. These resonators interact with each other via a phase-dependent phonon-exchange mechanism, which is coupled to the same nitrogen vacancy (NV) centers in diamond. Based on the modulation of the phonon–phonon coupling phase and leveraging the triple Fano-like resonance phenomenon, a tripling of electromagnetically induced transparency (EIT) becomes achievable within the system. This tripling is accompanied by swift dispersion, leading to a subtle advancement or delay in outcomes. The phenomenon of triple Fano-like resonance, alongside the resulting triple EIT, engenders noteworthy slow-to-fast and fast-to-slow light effects, which is theoretically demonstrated in CNT resonators, with both identical and distinct frequencies. The findings underscore that CNT resonators with varying frequencies can evoke a more pronounced transition in the slow–fast–slow and fast–slow–fast light effects. This study lays the foundation for the application of phonon-mediated optical information storage and processing.

Electromagnetically induced transparency enabled by quasi-bound states in the continuum modulated by epsilon-near-zero materials.

Highly tunable electromagnetically induced transparency (EIT) with high-quality-factor (Q-factor) excited by combining with the quasi-bound states in the continuum (quasi-BIC) resonances is crucial for many applications. This paper describes all-dielectric metasurface composed of silicon cuboid etched with two rectangular holes into a unit cell and periodically arranged on a SiO2 substrate. By breaking the C2 rotational symmetry of the unit cell, a high-Q factor EIT and double quasi-BIC resonant modes are excited at 1224.3, 1251.9 and 1299.6 nm with quality factors of 7604, 10064 and 15503, respectively. We show that the EIT resonance is caused by destructive interference between magnetic dipole resonances and quasi-BIC dominated by electric quadrupole. Toroidal dipole (TD) and electric quadrupole (EQ) dominate the other two quasi-BICs. The EIT window can be successfully modulated with transmission intensity from 90% to 5% and modulation depths ranging from -17 to 24 dB at 1200-1250 nm by integrating the metasurface with an epsilon-near-zero (ENZ) material indium tin oxide (ITO) film. Our findings pave the way for the development of applications such as optical switches and modulators with many potential applications in nonlinear optics, filters, and multichannel biosensors.

Enhancement of Entanglement via Incoherent Collisions.

In contrast to the general thought that the collisions are intrinsically dephasing in nature and detrimental to quantum entanglement at room or higher temperatures, here, we show that in the conventional ladder-type electromagnetically induced transparency (EIT) configuration, when the probe field intensity is not very weak as compared to the pump field, the entanglement between the bright pump and probe fields can be remarkably enhanced with the increase of the collisional decay rates in a moderate range in an inhomogeneously broadened atomic system. The strengthened entanglement results from the enhancement of constructive interference and suppression of destructive interference between one-photon and multiphoton transition pathways. Our results clearly indicate that the collisions offer a promising alternative to enhance entanglement at room or higher temperatures despite of the dephasing nature, which provides great convenience for experimental implementation, and opens new prospects and applications in realistic quantum computation and quantum information processing.

Enhanced microwave-atom coupling via quadrupole transition-dressed Rydberg atoms

The power broadening of a coupling laser can be converted into two-photon detuning by electromagnetically induced transparency (EIT), resulting in a residual Doppler effect. The residual Doppler effect in a ladder-type EIT in a room-temperature atom ensemble is further amplified through a wavelength mismatch effect between the probe and coupling laser beams, which reduces the atomic coupling of light or microwaves. We measured the Rydberg spectra of the electric dipole (E1) and electric quadrupole (E2) microwave transitions, demonstrating that the reduction in the Rydberg EIT signal can be recovered through far-off-resonance E2 microwave transition dressing and achieving an 8-dB enhancement in the Rydberg EIT signal. The frequency-dependent dressing of the E2 transition enables the shift of the dressed Rydberg states to be tuned, thereby providing a scalable approach to optimize the interaction between the Rydberg state and microwave field.

Analog electromagnetic induced transparency of T-type Si-based metamaterial and its applications

A T-type silicon-based metamaterial is proposed, which realizes electromagnetically induced transparency (EIT) by using the asymmetry of its structure. This dielectric metamaterial exhibits an ultranarrow EIT transparent window, with a transmittance of 91% and a Q factor of 180. Measuring its sensing performance, a refractive index sensor with a sensitivity of 466 nm RIU−1 is obtained. In addition, by analyzing the dispersion characteristics of the structure, the maximum group delay value is 2.84 ps, and the corresponding group refractive index is 4250. Therefore, dielectric metamaterials with this structure are expected to be used in refractive index sensing and slow light devices.

Active control of polarization-dependent terahertz surface plasmonic wave excitation using coupled graphene-metal hybrid metasurfaces

Active control of terahertz surface plasmonic wave (SPW) intensity in the propagation direction holds substantial significance for advanced terahertz functional devices. In this study, we propose a graphene-metal hybrid split-ring slit resonator (SRSR) array metasurfaces and employ the concept of electromagnetically induced transparency (EIT) to achieve excitation of asymmetric SPWs under various polarization states. By individually integrating two graphene ribbons into the two split-ring slit gaps and applying different bias voltages, we observed a gradual transition in the excitation behavior of asymmetric terahertz SPWs, ultimately resembling that of a single SRSR. Near-field simulations reveal that this phenomenon is attributed to the short-connection effect of graphene. Our proposed graphene-metal active hybrid metasurface introduces a novel approach to realize active SPWs devices, holding potential applications in terahertz on-chip communication.

Experimental validation of group delay in a multi-window electromagnetically induced transparency metasurface

Metasurface analogs of electromagnetically induced transparency (EIT) are attracting sustaining attention due to their ability to maintain transparency windows accompanied by extreme dispersion of propagating waves, which are important for slow light devices and highly sensitive optical sensors. In this paper, we study theoretically, numerically, and experimentally the conditions for the existence of multi-band transparency windows in the metasurface supported by the interaction of dipole modes in an asymmetric unit cell. The unit cell is composed of a single bright resonator and several dark resonators made in the form of rectangular metal patches. The manifestation of EIT is studied for different metasurface configurations by varying the number and positions of resonators used within the unit cell. To validate the slow-down effect caused by EIT, a prototype of the metasurface is fabricated and tested, providing a measurement of the group delay and bandwidth-delay product features. The obtained results clearly confirm the presence of four EIT-like transparency windows in the metasurface transmission spectra originating from the coupling between either quasi-TE or quasi-TM modes of the resonators.

Colossal Kerr nonlinearity without absorption in a five-level atomic medium

In this work, we present an analytical method to achieve giant Kerr nonlinearity without absorption in a five-level atomic medium. By using iterative perturbation technique on density matrix equations, we have derived the analytical expressions of nonlinear susceptibility and Kerr nonlinear coefficient in the presence of spontaneously generated coherence (SGC) and relative phase between applied laser fields. It shows that, this five-level atomic medium exhibits multiple electromagnetically induced transparency (EIT) at three different frequencies, at the same time, the Kerr nonlinear coefficient is enhanced around three transparent spectral regions; in each such EIT region appears a pair of positive–negative peaks of Kerr nonlinear coefficient. In particular, these nonlinear peaks are moved to the center of the EIT windows via SGC. This means that the Kerr nonlinear coefficient is enhanced with completely suppressed absorption at different transparency frequencies. Furthermore, the magnitude and the sign of the Kerr nonlinear coefficient are easily controlled according to the SGC strength, the coupling laser intensity, and the relative phase between applied laser fields. Such a giant nonlinear medium can be useful for photonic devices working in the resonant frequency region without absorption. As a typical application, this giant Kerr nonlinear material has been applied to an interferometer for the formation of optical bistability, and showed the appearance of OB at the resonant frequency with significantly reduced threshold intensity and OB width.