EIT Resonance Research Articles

Influence of buffer gas on the formation of N-resonances in rubidium vapors

The N-resonance process is an accessible and effective method for obtaining narrow (down to subnatural linewidth), and contrasted resonances, using two continuous lasers and a Rb vapor cell. In this article, we investigate the impact of buffer gas partial pressure on the contrast and linewidth of N-resonances formed in the D1 line of a 85Rb thermal vapor. N-resonances are compared to usual EIT resonances, and we highlight their advantages and disadvantages. Measurements were performed with five vapor cells, each containing Rb and Ne buffer gas with different partial pressures (ranging from 0 to 400 Torr). This reveals the existence of an optimum Ne partial pressure that yields the best contrast, for which we provide a qualitative description. We then study the behavior of the N-resonance components when a transverse magnetic field is applied to the vapor cell. The frequency shift of each component is well described by theoretical calculations.

Polarization conversion filter based on electromagnetically induced transparency-like effect

Owing to the large losses in the conversion process of traditional polarization converters, there is an increasing demand for metasurfaces with excellent transmission performance. In this work, an efficient polarization conversion metasurface is proposed based on electromagnetically induced transparency-like (EIT-like) effect in the terahertz band. The multi-level bright mode paths are excited by an asymmetric structure to obtain orthogonal circular polarization conversion windows. The transmission window is generated by the mutual interference of two sets of bright modes with similar resonant frequencies. Then an asymmetric structure is constructed to achieve transmission window shift under TE polarization and TM polarization, thereby realizing dual-frequency polarization conversion. The metamaterial unit structure consists of four open metal resonant rings and four metal resonant strips. The working mechanism is explored by analyzing the surface current distribution, frequency response, and incident angle characteristics. The results show that electromagnetically induced transparency can be achieved under different polarizations. Furthermore, based on the EIT resonance between the two incident polarizations, the conversion from linear polarization to right-hand circular polarization is achieved at 0.692 THz, and the conversion from linear polarization to left-hand circular polarization is realized at 0.782 THz, transmission coefficients are 0.7 and 0.68 respectively. According to the Stokes parameters, the corresponding ellipticity <i>η</i> values are 96% and 98%, respectively. This EIT-based polarization conversion metasurface with low loss and ultra-thin characteristics has great potential applications in compact antennas, derived radar phased arrays, and military detectors.

Two-Photon Laser Excitation of Rb Rydberg Atoms in the Magneto-Optical Trap and Vapor Cell

We present our experimental results of two-photon laser excitation 5S1/2→5P3/2→nS1/2 of Rb atoms to Rydberg nS1/2 states with a homemade 480 nm laser in the second excitation step. In an experiment with cold Rb atoms, we excited the 42S1/2 state and detected Rydberg atoms with a selective-field-ionization (SFI) detector that provides single-atom resolution. The resonance line shapes well agreed with numerical simulations in a three-level theoretical model. We also studied the multiatom spectra of Rydberg excitation of mesoscopic atom ensembles which are of interest to quantum information processing. In the experiment with hot Rb atoms, we first excited the 30S1/2 state and observed a narrow Rydberg EIT resonance. Its line shape also agreed well with theory. Then, we performed a similar experiment with the higher 41S1/2 state and observed the Autler–Townes splitting of the EIT resonance in the presence of a microwave field, which was in resonance with the microwave transition 41S→41P3/2. This allowed us to measure the average strength of the microwave field and, thus, demonstrate the operation of a Rydberg microwave sensor. We may conclude that the developed homemade laser at 480 nm substantially extends our capabilities for further experiments on quantum information and quantum sensing with Rydberg atoms.

Formation of strongly shifted EIT resonances using “forbidden” transitions of Cesium

Atomic transitions satisfying Fe−Fg=ΔF=±2 (where Fe stands for excited and Fg stands for ground state) of alkali atoms have zero probability in zero magnetic field (they are so-called ”forbidden” transitions) but experience a large probabilty increase in an external magnetic field. These transitions are called magnetically induced (MI) transitions. In this paper, we use for the first time the σ+ (ΔmF=+1) MI transitions Fg=3→Fe=5 of Cesium as probe radiation to form EIT resonances in strong magnetic fields (1 - 3 kG) while the coupling radiation frequency is resonant with Fg=4→Fe=5σ+ transitions. The experiment is performed using a nanometric-thin cell filled with Cs vapor and a strong permanent magnet. The thickness of the vapor column is 852 nm, corresponding to the Cs D2 line transition wavelength. Due to the large frequency shift slope of the MI transitions (∼ 4 MHz/G), it is possible to form contrasted and strongly frequency-shifted EIT resonances. Particularly, a strong 12 GHz frequency shift is observed when applying an external magnetic field of ∼ 3 kG. Preliminary calculations performed considering Doppler-broadened three level systems in a nanocell are in reasonable agreement with the experimental measurements.

Optical Spectral Shaping Based on Reconfigurable Integrated Microring Resonator-Coupled Fabry–Perot Cavity

We demonstrate a multifunctional optical spectral shaper on a silicon photonic chip. The proposed structure is composed of a tunable microring resonator (MRR) and three tunable Sagnac loop mirrors (SLMs), which can be regarded as a large SLM incorporating an MRR-coupled Fabry–Perot (FP) cavity. To realize flexible tuning, thermo-optically tunable Mach-Zehnder interferometer (MZI) couplers are used to replace conventional directional couplers with fixed coupling coefficients. By controlling the tunable MZI couplers, the proposed structure can be reconfigured as various functional structures including an all-pass MRR with tunable coupling regime, a tunable FP cavity, an SLM incorporating FP cavity, and an MRR-coupled FP cavity. This flexible reconfiguration allows for multifunctional optical spectral shaping including tunable comb filtering, Fano and EIT-like resonances. In particular, the complementary flat-top comb filtering responses can be theoretically obtained in the two ports of this device with same free spectral range (FSR) value, which enable the (de)interleaver operation. The experimental results show that the implemented all-pass MRR has a maximum extinction ratio (ER) of 38.9 dB and the corresponding quality factor is 6.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The comb filter based on configured FP cavity can be switched from narrowband response (0.06 nm) to wideband flat-top response (0.23 nm), with ERs up to 10.6 dB and 22 dB, respectively. Moreover, a dynamic conversion between Lorentz, EIT, and Fano resonance line shapes based on the coupled resonant system can be realized. The demonstrated integrated device holds great potential for various applications such as filtering and switching in optical wavelength-division multiplexing (WDM) communication networks.

RF E-field Sensing Using Rydberg Atom-Based Microwave Electrometry

In this work, a microwave field is sensed by rubidium atoms instead of a conventional antenna like dipole or horn antenna. Microwave field is projected onto a glass cell containing Rb vapors which act as an antenna in this case. A four-level ladder atomic system is considered for analytical solution, and E-field measurement is reported by utilizing quantum phenomena like electromagnetically induced transparency and Autler–Townes splitting. It has been shown that atoms can also sense weak microwave field with this approach. The amplitude measurement of microwave E-field is changed to frequency measurement, and E-field is evaluated by monitoring the frequency difference between two EIT peaks. Measurement results are reported for variable input microwave power at frequency 15.09 GHz varying from 12.5 μW to 4 mW generated from synthesized signal generator. Moreover, the effect on the EIT resonance due to the distance variation of the source antenna is also discussed. The microwave frequency is detuned from the resonant frequency, and results are reported in this work.

A detailed study of the quantum coherent and saturating resonances using the hyperfine lines of rubidium

We have studied both experimentally and theoretically the V-type system in the hyperfine structure of the D1 and D2 lines of rubidium with co-propagating pump-probe laser fields. The experimental observation in the V-type system shows the high contrast EIT peak along with the saturation peaks in the probe Doppler profile. A velocity dependent analysis regarding the formations and frequency positions of the observed resonances has been done. The dependence of the EIT line shape on the variation of the pump laser intensity and detuning has been investigated. It is observed that the EIT resonance disappears for a pump power when it is less than the probe power and the saturating effects dominate over the coherence effects in the system. By properly tuning the pump laser, a perfectly symmetric EIT peak with high contrast is obtained at the center of the probe Doppler profile, while the strong saturating resonances get eliminated. A theoretical model based on the density matrix formulation has been presented corresponding to a five-level V-configuration. This model helps us to interpret the experimental observation theoretically.

Polarization dependence of the optical properties in a Ξ system with an external magnetic field

We study optical properties of a three-level Ξ system in the presence of an external magnetic field for 87Rb and 85Rb atoms using density matrix formalism. The optical spectra in hyperfine linear Zeeman regime modify and we observe splitting in the single EIT window. The polarization of field in atom’s frame and transition strengths between Zeeman sub-levels are no more the same after applying an external magnetic field. The possible transition routes of non-degenerate magnetic sub-levels result in the splitting of a single EIT window to multiple narrow EIT sub-windows. Light propagation behavior of non-degenerate states of the system shows sub-and super-luminal regimes. Through our calculation we attribute the splitting to the broken degeneracy of hyperfine levels and the positions of EIT resonance.

Transit Ramsey EIT resonances in a Rb vacuum cell

We investigate a dual-channel arrangement for electromagnetically-induced transparency in a vacuum Rb vapor cell, and report the observation of a transient spectral feature due to the atoms traversing both beams while preserving their ground-state spin coherence. Despite a relatively small fraction of atoms participating in this process, their contribution to the overall lineshape is not negligible. By adjusting the path difference between the two optical beams, the differential intensity measurement can produce an error signal for the microwave frequency stabilization as strong as a single-channel measurement, but it provides a much higher signal-to-noise ratio due to the cancellation of intensity noise, dominating the signal channel detection.

Tunable multispectral plasmon induced transparency based on graphene metamaterials

A dynamically wavelength tunable multispectral plasmon induced transparency (PIT) device based on graphene metamaterials, which is composed of periodically patterned graphene double layers separated by a dielectric layer, is proposed theoretically and numerically in the terahertz frequency range. Considering the near-field coupling of different graphene layers and the bright-dark mode coupling in the same graphene layer, the coupled Lorentz oscillator model is adapted to explain the physical mechanism of multispectral EIT-like responses. The simulated transmission based on the finite-difference time-domain (FDTD) solutions indicates that the shifting and depth of the EIT resonances in multiple PIT windows are controlled by different geometrical parameters and Fermi energies distributions. A design scheme with graphene integration is employed, which allows independent tuning of resonance frequencies by electrostatically changing the Fermi energies of graphene double layer. Active control of the multispectral EIT-like responses enables the proposed device to be widely applied in optical information processing as tunable sensors, switches, and filters.

Transformation of electromagnetically induced transparency into absorption in a thermal potassium optical cell with spin preserving coating

We report a new experimental approach where an order of magnitude enhancement of the electromagnetically induced absorption (EIA) resonance contrast, thus making it similar to that of the EIT resonance contrast is observed under the same conditions. The EIA signal results from the interaction of a weak probe beam with a ground state that has been driven by the pump (counter-propagating) beam. Probe absorption spectra are presented where the laser frequency is slowly detuned over the D1 line of 39K vapor contained in a cell with a PDMS antirelaxation coating. In addition to the frequency detuning, a magnetic field orthogonal to the laser beams is scanned around zero value at a higher rate. With both laser beams linearly polarized, an EIT resonance is observed. However, changing the pump beam polarization from linear to circular reverses the resonance signal from EIT to EIA.

EIT resonance features in strong magnetic fields in Rubidium atomic columns with length varying by 4 orders

EIT resonance features in strong magnetic fields in Rubidium atomic columns with length varying by 4 orders

Investigation of quantum coherence effects in a multilevel atom induced by three laser fields

In this work, we report a detail theoretical study to understand the quantum coherence processes induced by three laser fields in a multilevel atom. In one of the coupling scheme using three laser fields we have theoretically simulated the EIA and EIT resonances simultaneously in a single probe transmission profile. It has been shown that these two coherent resonances of opposite kinds can be tuned at any position of the probe profile and they cancel out when they are completely merged together. We have also theoretically calculated the dual-EIT as well as a single EIT resonance with improved contrast in an N-type scheme. It has been shown that the contrast of the V-type EIT is greatly enhanced in the N-type system when it is tuned to the position of Λ-type EIT. We have examined the atomic density effect on the enhanced N-type EIT resonance and it has been shown that the nature of variation of the line shape of this pronounced EIT resonance strongly depends on the variations of the individual Λ- and V-type EIT with atomic density. Theoretically simulated spectra have been compared with the experimental observations in rubidium vapour with its natural abundances. For the experimental comparison of the observed resonances under different atom-laser coupling schemes, we have used the D 2 transition (5S1/2–5P3/2) of 85Rb isotope. A good agreement is found between the simulated results and the experimental spectra.

Tunneling Control of Optical Properties of a Quantum Well from Adjacent Quantum Well by Coherent Population Trapping Effect

Now the coherent population trapping (CPT) effect attracts a big researcher’s interest. The essence of this effect is the appearing of specific superposition of long-lived states in multilevel quantum system interacting with two-frequency coherent (usually laser) field. This superposition state (dark state) is not interacts with the field. The dark resonances were investigated theoretically [1, 2] as well as experimentally in semiconductor quantum wells in the basis of InGaAs/AlInAs and GaAs [3]. The dark resonances are of particular interest for the development of devices for recording and storing of quantum information and also for quantum logic elements. So the methods of recording and reading of qubits with a high degree of fidelity were realized on the basis of the EIT resonance in the atoms inside an optical lattice. In this work we investigate the CPT effect in the double tunnel-coupled quantum wells interacting with laser radiation 1,2,3  (Fig.1). The microwave field V closes the contour of excitation (-system). We found that it is possible to create the specific collapse of population (dark resonance), which takes place for the excited level of simple -system, for the ground level 3 of additional excitation canal. Moreover, destruction and restoration of CPT by variation of the total phase Ф (Fig.1) of exciting fields in the -system gives us the possibility to control population of the ground level 3 . We investigate the cases of constant and pulsed optical radiation. In the case of pulsed radiation we found that only edges of signal pulse are absorbed. Middle of the pulse does not interact with the quantum wells due to dark state of the level 3 . It can be useful for reducing of the pulse duration and generation of the higher harmonics. This work is supported by Russian President grant for young candidates of sciences (project МК-384.2013.2), non-profit foundation Dynasty, Russian Foundation for Basic Research (project 14-02-31422), Regional Public Science Support Foundation, British Petroleum company, State Assignment for universities 2014/184.

Study of the splitting of electromagnetically induced transparency resonance in strong magnetic field using Rb nano-thin cell

Recently we have obtained the high-contrast electromagnetically induced transparency resonance on 85Rb and 87Rb D1 line in nanometric-thin cell of L = λ = 794 nm thickness. In present work we exploit the 40% contrast of EIT resonance to study its splitting in a very wide range of a B-field covering, for the first time, 1 – 1700 G region. Experimental results are fully consistent with the developed theoretical model.

Dark Hanle resonances from selected segments of the Gaussian laser beam cross-section

We present the Hanle EIT resonances obtained from the various segments of the Gaussian laser beam cross-section, selected by moving the small aperture (placed in front of the detector) radially along the laser beam. Significant differences in the Hanle lineshapes are observed depending on whether the central or outer parts of the Gaussian laser beam are detected. The line narrowing and two counter-sign peaks occur at outer, less intense parts of the beam. The theoretical model suggests that the EIT lineshapes in the laser wings are result of the interference of the laser light and coherently prepared atoms coming from the central part of the beam. By blocking the central part of the laser beam in front of the detector, narrower, and for high laser intensities, even more contrasted Hanle resonances are obtained.

Phase shift caused by microwave field based on light storage

We have theoretically investigated the phase shift of a probe field for a four-level atomic system interacting successively with two fields tuned near an EIT resonance of an atom, a microwave field, and a coupling field. It has been found that the phase of retrieved signal has been shifted due to the cross-phase modulation when the stored spin wave was disturbed by a microwave. Because of the low relaxation rates of the ground hyperfine state, our proposed technique can impart a large phase rotation onto the probe field with low absorption of retrieved field and very low intensity of the microwave field.

Interference effects in the two-colour excitation of the sodium atom

The steady state of the density matrix is analysed for the two-colour light beam resonantly coupled to the different transitions between the lower S 1/2 and upper P 1/2 sodium hyperfine levels, F=1 and 2. Particularly, the populations, the contributions to the transition dipole moments and the Raman coherences have been calculated for various beam intensities and detunings. The width of the EIT resonance has been found to be entirely due to the collisional destruction of the ground-state Raman coherence and the power broadening. Therefore, the corresponding profile is very narrow for the weak field, as compared with the spectral line shape. In the case of sufficiently strong coupling beam, the dynamical Stark effect is dominant. We have found that the position of the EIT resonance does not depend on the field intensities of the coupling and probe beams.

Narrowing of electromagnetically induced transparency resonance in a Doppler-broadened medium

We derive an analytic expression for the linewidth of EIT resonance in a Doppler broadened system. It is shown here that for relatively low intensity of the driving field the EIT linewidth is proportional to the square root of intensity and is independent of the Doppler width, similar to the laser induced line narrowing effect by Feld and Javan. In the limit of high intensity we recover the usual power broadening case where EIT linewidth is proportional to the intensity and inversely proportional to the Doppler width.