Electromagnetically Induced Transparency Window Research Articles

Controllable ultra-narrow fluorescence and six-wave mixing under double electromagnetically induced transparency

We report the first observation of six-wave mixing (SWM) and fluorescence signals in an electromagnetically induced transparency (EIT) window. Several remarkable advantages are described. First, multiple bright and dark states are simultaneously observed due to enhancement or suppression of the SWM signal. Second, ultra-narrow fluorescence, much narrower than the EIT window, is experimentally obtained. Third, the ultra-narrow fluorescence can also generate Autler–Townes splitting on scanning the coupling beam. Fourth, a double-peak EIT window is obtained using the nest-dressing scheme. Such studies concerning SWM and fluorescence have applications in optical switching, multi-channel communication and narrowband and long-range quantum communication.

A dynamically reconfigurable Fano metamaterial through graphene tuning for switching and sensing applications

We report on a novel electrically tunable hybrid graphene-gold Fano resonator. The proposed metamaterial consists of a square graphene patch and a square gold frame. The destructive interference between the narrow- and broadband dipolar surface plasmons, which are induced respectively on the surfaces of the graphene patch and the gold frame, leads to the plasmonic equivalent of electromagnetically induced transparency (EIT). The response of the metamaterial is polarization independent due to the symmetry of the structure and its spectral features are shown to be highly controllable by changing a gate voltage applied to the graphene patch. Additionally, effective group index of the device is retrieved and is found to be very high within the EIT window suggesting its potential use in slow light applications. Potential outcomes such as high sensing ability and switching at terahertz frequencies are demonstrated through numerical simulations with realistic parameters.

Comparison of Ultranarrow Fluorescence and Four-Wave Mixing in Electromagnetically Induced Transparency Windows

We simultaneously observe the probe transmission, four-wave mixing (FWM) and fluorescence signals under dressing effects in a four-level -type atomic system for the first time. The physical mechanisms of three types of signals are explored by changing the frequency detuning and power of incident laser beams. Especially, the ultranarrow fluorescence signals have been experimentally obtained due to twice shearing by electromagnetically induced transparency (EIT) window, which are much narrower than the Doppler-free EIT window. Such ultranarrow fluorescence signals with very high coherence and monochromaticity have potential applications in the quantum correlation and narrow linewidth laser. Studying the FWM processes can find applications in optical switch and optical communication.

Electromagnetically induced transparency of single Λ-type three-level atoms in a high-finesse optical cavity

We study the features of electromagnetically induced transparency (EIT) in a single Λ-type three-level atom placed in a high-finesse cavity under the action of a coupling laser and a probe laser. Our calculations show that three transparency windows appear when the pump strength is large enough. This can be explained by the residual pump in the cavity mostly resulting in energy splitting. The level |3〉 is split into four slightly different energy levels, and interference takes place between the excitation pathways. Furthermore, it is also shown that the frequencies of the EIT windows can be tuned by changing the coupling field detuning Δ2, and that the reflection profile is very sensitive to the cavity field detuning Δc.

All-atomic generation and noise-quadrature filtering of squeezed vacuum in hot Rb vapor

With our all-atomic squeezing and filtering setup, we demonstrate control over the noise amplitudes and manipulation of the frequency-dependent squeezing angle of a squeezed vacuum quantum state by passing it through an atomic medium with electromagnetically induced transparency (EIT). We generate low sideband frequency squeezed vacuum using the polarization self-rotation effect in a hot Rb vapor cell, and direct it through a second atomic vapor subject to EIT conditions. We use the frequency-dependent absorption of the EIT window to demonstrate an example of squeeze amplitude attenuation and squeeze angle rotation of the quantum noise quadratures of the squeezed probe. These studies have implications for quantum memory and storage as well as gravitational wave interferometric detectors.

Wave-vector mismatch effects in electromagnetically induced transparency inY-type systems

We study electromagnetically induced transparency (EIT) of a probe field in a four-level Y-type atomic system driven by two strong laser (coupling) fields. Both homogeneously (radiative) and Doppler broadened systems are considered. The effect of residual Doppler broadening on EIT is demonstrated for various wave-vector mismatches occurring when the frequency of coupling fields is equal (${k}_{c}$ $=$ ${k}_{p}$), higher (${k}_{c}>{k}_{p}$), or lesser (${k}_{c}<{k}_{p}$) than that of the probe field frequency. Contrary to usual belief it is found that for the ${k}_{c}>{k}_{p}$ wave-vector mismatch case, the probe absorption profile displays very wide and almost complete single or double EIT windows whose width, depth, and location depend upon the wave-vector mismatch, Rabi frequencies, and atom field detuning of the coupling fields. Analytical results are also obtained to explain these interesting features.

Experimental Identification of Electromagnetically Induced Transparency in Magnetized Plasma

We report the first experimental identification of the new wave branch at electron cyclotron frequency produced by the injection of a frequency-matched intense pump wave in magnetized plasma [A. G. Litvak and M. D. Tokman, Phys. Rev. Lett. 88, 095003 (2002); G. Shvets and J. S. Wurtele, Phys. Rev. Lett. 89, 115003 (2002)], which is a classical phenomenon analogous to electromagnetically induced transparency (EIT) in quantum systems. By using a frequency-sweep interferometer, we directly detected the dispersion relation of the plasma EIT branch for propagation parallel to the background magnetic field. The bandwidth of the EIT window was correlated with the pump-wave electric field and was found to agree with the theoretical prediction.

The effect of Doppler broadening on dispersive and absorptive properties in atomic systems with two-photon interference

The effect of Doppler broadening on dispersive and absorptive properties is theoretically investigated in the hot four-level electromagnetically induced transparency (EIT) atomic systems with two different types of two-photon interference. It is found that the dispersive behavior for the probe in the ladder-type atomic system with two-photon constructive interference will be changed from anomalous in cold atoms to normal in hot atoms, and the three-peak absorptive profile is shifted to a broadened spectrum with a shallow dip at the line center; as a comparison, there is always normal dispersion at the line center for the invert-Y-type atomic system with two-photon destructive interference, but the EIT window in the absorptive profile will be narrowed to subnatural linewidth (0.01 Γ) at room temperature. The physics of those two different behaviors are discussed and compared in the dressed-state theory.

Interference of three multiwave mixings via electromagnetically induced transparency

We experimentally observe the interplay among coexisting multiwave-mixing (MWM) signals via multiple electromagnetically induced transparency (EIT) windows, including two ladder-type EIT windows and one V-type EIT-like window in a five-level atomic system of Rb85. In the presence of these EIT windows, one can control the interplay between these MWM signals easily by changing the frequency detuning. Meanwhile, we also report the spatial and temporal interferences with a femtosecond time scale among three coexisting MWM signals in two overlapped EIT windows.

Electromagnetically induced transparency in an open V-type molecular system

We report the experimental observation of electromagnetically induced transparency (EIT) in an inhomogeneously broadened V-type Na2 molecular system. The experiment is performed with both co- and counterpropagating arrangements for the propagation directions of the coupling and probe laser beams. In our theoretical model we employ the density matrix formalism, as well as perturbative methods for obtaining the probe field absorption profile for both open and closed systems. Simulations of the experimental data show excellent agreement with the predictions derived from the basic theory. Our fluorescent intensity measurements show that, in the copropagating configuration, the EIT plus saturation window depth is about 95%, while under similar conditions in the counterpropagating geometry we observed 40%‐45% reduction in the fluorescence signal around the line center. To separate the two simultaneously occurring mechanisms in a V-type system (i.e., EIT and saturation) that are induced by the coupling field, we have carried out theoretical calculations which show that, in the copropagating case, a significant fraction of the depth of the dip is due to the coherent effect of EIT. When the coupling and probe beams are in the counterpropagating configuration, the dip is mostly due to saturation effects alone.

Switching enhancement and suppression of four-wave mixing via a dressing field

The switch between the enhancement and suppression of the four-wave mixing (FWM) process in an electromagnetically induced transparency (EIT) window via quantum interference has been demonstrated experimentally. The enhancement and suppression of the FWM signal, as well as the EIT window, switch with a change in the probe detuning. Also, by controlling the powers of the dressing and probe fields, the enhancement and suppression of the FWM signal can be switched and an optimized enhancement can be obtained. Such a switch of the enhancement and suppression of the FWM signal intensity can find potential applications in optical switches, optical communication and quantum information processes.

Phase-dependent electromagnetically induced transparency in a four-level atom system

We present a method to control the electromagnetically induced transparency (EIT) in a four-level system with a coupling field, a weak probe field and two microwave driven fields. By sloving the density matrix equations, the numerious result is obtained. It is shown that the EIT resonance can be split into doublets and the spectral position of EIT window is determined by the relative phase between two microwave fields for fixed intensity of the microwave field. Therefore, the microwave field can be used to open more than one EIT window and by controlling their phase difference we can perform EIT frequency tuning. The structure in the spectrum can be explained using the dressed-state formalism.

Enhancing and suppressing four‐wave mixing in electromagnetically induced transparency window

AbstractWe demonstrate the enhancement and suppression of four‐wave mixing (FWM) in an electromagnetically induced transparency (EIT) window in Y‐type 85Rb atomic system. The generated two‐photon FWM signal can be selectively enhanced and suppressed via an EIT window. The EIT of probe as well as the enhancement and suppression of FWM signals can be modified by the sequential‐cascade double dressing. The influence of different probe polarization configurations is also studied. Different polarization states of the probe laser can select different transitions among Zeeman sublevels and different dressing strengths. Copyright © 2010 John Wiley & Sons, Ltd.

Double dark resonances and the dispersion properties in a four-level inverted-Y atomic system

The electromagnetically induced transparency (EIT) and its dispersion properties in a four-level inverted-Y atomic system are investigated. The absorption spectrum of a weak probe field shows two EIT windows (dark resonances) whose location, width, and depth can be controlled by manipulating the parameters of the coupling fields; the corresponding dispersion properties are also measured by using a Mach–Zehnder interferometer. The experimental measurements agree well with the theoretical calculations. This kind of system can find important applications in two-channel quantum communication and information storage.

EIT-assisted large cross-Kerr nonlinearity in a four-level inverted-Y atomic system

A four-level inverted-Y scheme with an electromagnetically induced transparency (EIT) core is investigated for the enhancement of cross-Kerr effect in rubidium atoms. When detunings of the coupling and control fields are appropriately set, an enhanced EIT window is observed, and the induced phase shift of the probe field due to cross-phase modulation (XPM) is obtained by measuring the dispersive property of the probe transition. The maximal XPM phase shift is about 12° under the current experimental conditions. The experimental measurements agree well with the theoretical calculations. The enhanced XPM phase shift in such an atomic system has applications in quantum nonlinear optics and quantum information science.

A new way of broadening the EIT window: Control over subluminal group velocity

The broadening of the Electromagnetically induced transparency (EIT) window can be achieved in a three level closed A system by controlling the strength of incoherent pumping. It has been shown that the presence of homogeneous/inhomogeneous decay facilitates the EIT window broadening. Moreover control over the subluminal group velocity associated with EIT can be achived by manipulating the number density of the molecules. This effect has been demonstrated in a heteronuclear molecule (e.g. LiH).

Two-way transparency in the light-matter interaction: Optical precursors with electromagnetically induced transparency

We theoretically study classical step-modulated pulse propagation in an optically thick medium with electromagnetically induced transparency (EIT) using a fast Fourier transform and a proposed hybrid-asymptotic analysis. The 100% transmitted leading edge traveling at $c$ consists of Sommerfeld-Brillouin precursors. The main signal, falling inside of the narrow EIT window, experiences a steep dispersion and slow group velocity. We suggest active control of the precursors and main signal separately by adjusting the parameters of the medium and incident pulse.

Electromagnetically induced transparency induced by a 100% amplitude-modulated coupling field

We present a study of electromagnetically induced transparency (EIT) under the excitation of a 100% amplitude-modulated (AM) coupling field. The EIT feature is associated with a Λ type three-level configuration where a coupling and probe field couples two separate optical transitions and it is well-known that the spectrum of the swept probe field gives a simple single transparency feature induced by the single mode coupling field. It is shown that when a 100% AM coupling field is applied, there is an EIT doublet and the separation of the EIT doublet can be controlled by the modulation frequency of the coupling field. Our result implies a new way of manipulating EIT resonance and opening more than one EIT windows.

Storage and retrieval of nonclassical photon pairs and conditional single photons generated by the parametric down-conversion process

Storage and retrieval of parametric down-conversion (PDC) photons are demonstrated with electromagnetically induced transparency (EIT). Extreme frequency filtering is performed for the THz order of broadband PDC light and the frequency bandwidth of the light is reduced to the MHz order. Storage and retrieval procedures are carried out for frequency-filtered PDC photons. Since the filtered bandwidth (full width at half-maximum (FWHM)=9 MHz) is within the EIT window (FWHM=12.6 MHz), the flux of the PDC light is successfully stored and retrieved. The nonclassicality of the retrieved light is confirmed by using the photon counting method, where the classical inequality that is only satisfied for classical light fields is introduced. Since PDC photons can be utilized for producing a single-photon state conditionally, storage and retrieval procedures are also performed for conditional single photons. The anticorrelation parameter used for checking the property of the single-photon state shows a value of less than 1, which means that the retrieved light is in a nonclassical region.

Power spectra and correlations of intensity fluctuations in electromagnetically induced transparency

The quantum fluctuations of optical beams are highly correlated in electromagnetically induced transparency (EIT). The intensity fluctuations are enhanced by conversion of phase noise to intensity noise in atomic vapour. We have studied spectra of intensity fluctuations in dense rubidium vapour for different laser beam powers. Observed excess noise spectrum is broader than EIT window at the same optical power. Both spectral widths are proportional to the laser beam intensity. By using signal subtraction scheme we can reduce amplitude of the fluctuations to close the photonic short noise level. This result confirms the high degrees of intensity correlations and can be used to improve quality of optical atomic clocks.