Three-level Configuration Research Articles

Electromagnetically induced transparency in a multilayered spherical quantum dot with hydrogenic impurity

In this paper the effects of size, hydrostatic pressure and temperature on electromagnetically induced transparency, as well as on absorption and the dispersion properties of multilayered spherical quantum dot with hydrogenic impurity are theoretically investigated. Energy eigenvalues and wavefunctions of quantum systems in three-level and four-level configurations are calculated using the shooting method, while optical properties are obtained using the density matrix formalism and master equations. It is shown that peaks of the optical properties experience a blue-shift with increasing hydrostatic pressure and red-shift with increasing temperature. The changes of optical properties as a consequence of changes in barrier wells widths are non-monotonic, and these changes are discussed in detail.

Cavity electromagnetically induced transparency with Rydberg atoms

Cavity electromagnetically induced transparency (EIT) is revisited via the input probe field intensity. A strongly interacting Rydberg atomic medium ensemble is considered in a cavity, where atoms behave as superatoms (SAs) under the dipole blockade mechanism. Each atom in the strongly interacting Rydberg atomic medium (Rb) follows a three-level cascade atomic configuration. A strong control and weak probe field are employed in the cavity with the ensemble of Rydberg atoms. The features of the reflected and transmitted probe light are studied under the influence of the input probe field intensity. A transparency peak (cavity EIT) is revealed at a resonance condition for small values of input probe field intensity. The manipulation of the cavity EIT is reported by tuning the strength of the input probe field intensity. Further, the phase and group delay of the transmitted and reflected probe light are studied. It is found that group delay and phase in the reflected light are negative, while for the transmitted light they are positive. The magnitude control of group delay in the transmitted and reflected light is investigated via the input probe field intensity.

Mixture of Electromagnetically Induced Transparency and Autler–Townes Splitting in a Five-Level Atomic System**Supported by the National Natural Science Foundation of China under Grant Nos. 11274132, 11547208, and the Science Foundation of China Three Gorges University

Discerning electromagnetically induced transparency (EIT) from Autler–Townes splitting (ATS) is a significant issue in quantum optics and has attracted wide attention in various three-level configurations. Here we present a detailed study of EIT and ATS in a five-level atomic system considered to be composed of a four-level Y-type subsystem and a three-level Λ-type subsystem. In our theoretical calculations with standard density matrix formalism and steady-state approximation, we obtain the general analytical expression of the first-order matrix element responsible for the probe-field absorption. In light of the well-known three-level EIT and ATS criteria, we numerically show an intersection of EIT with ATS for the Y-type subsystem. Furthermore, we show that an EIT dip is sandwiched between two ATS dips (i.e., multi-dip mixture of EIT and ATS) in the absorption line for the five-level system, which can be explained by the dressed-state theory and Fano interference.

A Fault-Tolerant Dual Three-Level Inverter Configuration for Multipole Induction Motor Drive With Reduced Torque Ripple

Multilevel inverters are gaining more attention in ac drive application due to their many attractive features. In the case of conventional neutral-point-clamped (NPC) or flying capacitor multilevel inverter configurations, active switches are connected in series to produce multilevel output voltage waveform. Therefore, if any one switch fails, the entire configuration has to be shut down; this will reduce the reliability of the system. A dual three-level inverter configuration for induction motor drive is proposed in this paper to improve reliability of the system. This topology is developed by feeding four-pole induction motor stator winding with four conventional two-level inverter modules. A level-shifted carrier-based third harmonic injection pulsewidth-modulation technique is used to produce the gating signals for the proposed configuration. By providing proper phase shift between carrier waves, multilevel voltage waveform is produced across the total motor phase winding, and first center band harmonics are also canceled. Thereby, the torque ripple will be considerably reduced compared with conventional NPC five-level inverter-driven induction motor drive. Finite-element analysis (FEA) is used to estimate the torque ripple when induction motor is supplied by the proposed configuration and conventional five-level NPC inverter configuration to show the effectiveness of the proposed converter. The proposed configuration is simulated using MATLAB/Simulink and experimentally verified using a laboratory prototype with a 5-hp four-pole induction motor drive.

Amplified light storage with high fidelity based on electromagnetically induced transparency in rubidium atomic vapor

By using slow and stored light based on electromagnetically induced transparency (EIT), we theoretically realize the storage of optical pulses with enhanced efficiency and high fidelity in ensembles of warm atoms in 85Rb vapor cells. The enhancement of storage efficiency is achieved by introducing a pump field beyond three-level configuration to form a N-type scheme, which simultaneously inhibits the undesirable four-wave mixing effect while preserves its fidelity. It is shown that the typical storage efficiency can be improved from 29% to 53% with the application of pump field. Furthermore, we demonstrate that this efficiency decreases with storage time and increases over unity with optical depth.

Modelling the regional variability of the probability of high trihalomethane occurrence in municipal drinking water.

The regional variability of the probability of occurrence of high total trihalomethane (TTHM) levels was assessed using multilevel logistic regression models that incorporate environmental and infrastructure characteristics. The models were structured in a three-level hierarchical configuration: samples (first level), drinking water utilities (DWUs, second level) and natural regions, an ecological hierarchical division from the Quebec ecological framework of reference (third level). They considered six independent variables: precipitation, temperature, source type, seasons, treatment type and pH. The average probability of TTHM concentrations exceeding the targeted threshold was 18.1%. The probability was influenced by seasons, treatment type, precipitations and temperature. The variance at all levels was significant, showing that the probability of TTHM concentrations exceeding the threshold is most likely to be similar if located within the same DWU and within the same natural region. However, most of the variance initially attributed to natural regions was explained by treatment types and clarified by spatial aggregation on treatment types. Nevertheless, even after controlling for treatment type, there was still significant regional variability of the probability of TTHM concentrations exceeding the threshold. Regional variability was particularly important for DWUs using chlorination alone since they lack the appropriate treatment required to reduce the amount of natural organic matter (NOM) in source water prior to disinfection. Results presented herein could be of interest to authorities in identifying regions with specific needs regarding drinking water quality and for epidemiological studies identifying geographical variations in population exposure to disinfection by-products (DBPs).

Cavity QED implementation of non-adiabatic holonomies for universal quantum gates in decoherence-free subspaces with nitrogen-vacancy centers.

A cavity QED implementation of the non-adiabatic holonomic quantum computation in decoherence-free subspaces is proposed with nitrogen-vacancy centers coupled commonly to the whispering-gallery mode of a microsphere cavity, where a universal set of quantum gates can be realized on the qubits. In our implementation, with the assistant of the appropriate driving fields, the quantum evolution is insensitive to the cavity field state, which is only virtually excited. The implemented non-adiabatic holonomies, utilizing optical transitions in the Λ type of three-level configuration of the nitrogen-vacancy centers, can be used to construct a universal set of quantum gates on the encoded logical qubits. Therefore, our scheme opens up the possibility of realizing universal holonomic quantum computation with cavity assisted interaction on solid-state spins characterized by long coherence times.

Analytical evaluation of output current ripple amplitude in three‐phase three‐level inverters

Nowadays, three-phase multilevel inverters are widely employed in medium and high-power applications, increasing the power ratings, improving the output voltage quality and reducing the conducted electromagnetic interferences. Despite of numerous pulse-width modulation (PWM) techniques have been developed for multilevel inverters, a detailed analysis of the output current ripple amplitude has not been reported yet. In this study, the peak-to-peak current ripple distribution over a fundamental period is analysed in details specifically for three-level three-phase voltage source inverters for both motor-load and grid-connected applications. In particular, the peak-to-peak amplitude of the current ripple is determined analytically as a function of the modulation index. The centred PWM strategy is considered in all the developments, implemented either by carrier-based or space vector (SV) PWM methods. With this modulation, the dc bus utilisation is maximised in a simple and effective way, and a nearly-optimal behaviour is obtained to minimise the current ripple rms. The results obtained in different cases and sub-cases identified in the proposed analytical approach are verified by experimental tests with reference to three-phase three-level neutral-point clamped configuration.

Phase effects on pulse propagation in atomic media in the triangular configuration

The subject of this work is the propagation of a weak probe pulse in an atomic medium in a three-level closed-loop configuration. An atomic system is irradiated with two strong control fields: optical and microwave. Two channels for the probe field are activated: (i) absorption of a probe photon and (ii) emission of a probe photon with the simultaneous absorption of two control and two microwave photons. We analyse in detail the pulse spectrum and its time–space evolution taking into account the generation of light by the atomic sample. In particular, we study interference effects due to the relative phase of the applied fields. In contrast to other papers, we do not make the assumption of net (three photon) resonance.

Modelling and Simulation of Direct Torque Controlled Induction Motor Drive using Slip Speed Control

In this paper an effective control strategy to reduce the torque and flux ripple in direct torque control (DTC) of induction motor drive based on a slip speed control of stator flux is presented. This control strategy is applied to three-level inverter configuration using cascaded two two-level inverters for improving the performance of the system. Torque control is achieved by reference stator flux angle which is generated from the sum of incremental change in stator flux angle and actual stator flux angle. Modelling and simulation of proposed DTC is presented and results of the simulation are compared with basic DTC. From the simulation results it is observed that the torque and flux ripple are less with proposed DTC and also an improvement in the steady-state performance of the drive system at high and low speed operation.

Multiphoton Rabi oscillations of a ringlike three-level system

We propose a ringlike three-level model and show that it can be realized using Stark states of highly excited potassium interacting with two-mode microwave fields. We demonstrate this by using both analytical model and numerical simulations to study the problems of multiphoton Rabi oscillations. The results show that the Rabi oscillation patterns of the ringlike three-level system exhibit additional envelope and nodes compared to the oscillatory behavior of a three-level cascade system; in other words, there exist collapse and revival phenomena for Rabi oscillation patterns. The origin of the collapse and revival of the population oscillations is the multiphoton two-color resonances at frequency $\ensuremath{\Omega}=n{\ensuremath{\omega}}_{1}+m{\ensuremath{\omega}}_{2}$. Our analytic results are in good agreement with numerical simulations. In addition, all the analytical solutions for the three basic configurations of the three-level system classified as the $\ensuremath{\Lambda}$, vee, and cascade systems can be deduced from our analytical solution for the ringlike three-level configuration by setting one of the three coupling strengths equal to 0.

Quantum-interference-controlled resonance profiles from lasing without inversion to photodetection

In this work we report a quantum interference mediated control of the resonance profiles in a generic three-level system and investigate its effect on key quantum interference (QI) phenomena. Namely in a three-level configuration with doublets in the ground or excited states, we show control over enhancement and suppression of the emission (absorption) profiles. This is achieved by manipulation of the strength of QI and the energy spacing of the doublets. We analyze the application of such QI-induced control of the resonance profile in the framework of two limiting cases of lasing without inversion and photodetection.

Dependence of Entanglement in a System of a Three-Level Atom Interacting with a Single Mode Field on the Three-Level Configuration

Dependence of Entanglement in a System of a Three-Level Atom Interacting with a Single Mode Field on the Three-Level Configuration

Polarization Control in Three-Dimensional Resonant Coherent Excitation

We present an experimental demonstration of an ingenious technique to control the alignment of the atomic internal state in the x-ray region using a periodic crystal field. The alignment directions of Ar16+ and Fe24+ ions were readily controlled by selecting the array of atomic planes using three-dimensional resonant coherent excitation, and were probed via the anisotropy of the deexcitation x-ray emission. We applied this method to a double resonance experiment, and succeeded in controlling the population of the specific magnetic substate in a Lambda-type three-level configuration.

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.

Dynamical symmetry breaking of lambda- and vee-type three-level systems on quantization of the field modes

We develop a scheme to construct the Hamiltonians of the lambda-, vee- and cascade-type three-level configurations using the generators of SU(3) group. It turns out that this approach provides a well-defined selection rule to give different Hamiltonians for each configuration. The lambda- and vee-type configurations are exactly solved with different initial conditions while taking the two-mode classical and quantized fields. For the classical field, it is shown that the Rabi oscillation of the lambda model is similar to that of the vee model and the dynamics of the vee model can be recovered from lambda model and vice versa simply by inversion. We then proceed to solve the quantized version of both models by introducing a novel Euler matrix formalism. It is shown that this dynamical symmetry exhibited in the Rabi oscillation of two configurations for the semiclassical models is completely destroyed on quantization of the field modes. The symmetry can be restored within the quantized models when both field modes are in the coherent states with large average photon number which is depicted through the collapse and revival of the Rabi oscillations.

Dark Resonances in Quantum Optics

Quantum control and quantum computation, representing two important directions of today research, rely on the precise modification of quantum mechanical systems not perturbed by an environment presence. This precise control was reached in different areas of physics using electromagnetic fields interacting with atoms or molecules in different matter phases. The simplest quantum mechanical system to be explored is a two-level atom, with lower and upper levels excited by a resonant or quasi-resonant electromagnetic field, as it occurs in nuclear or electronic magnetic resonance or in two-level laser spectroscopy. There the populations of the two levels or the coherence between the two levels are precisely modified by a control on the frequency, amplitude and interaction time of the electromagnetic field. The weak perturbation by the environment is realized, for instance, operating with low pressure or with cold/ultracold gases as produced by the combination of laser cooling and evaporative cooling techniques. The next step in level complexity is the three-level systems, with three levels, to be denoted as |0〉, |p〉, |c〉 excited by two separate lasers, the first probe laser at frequency ωp driving the transition |p〉 → |0〉 and the coupling laser at frequency ωc driving the transition |c〉 → |0〉. The atom–laser interaction of a three-level system is based on the evolution of the population of the three levels, of the optical coherences between levels |0〉, |p〉 and |0〉, |c〉. In addition, the three-level system may be prepared by the applied lasers in a coherent superposition state, whence it supports one high order coherence between levels |p〉 and |c〉. The build up of that coherence by the applied lasers produces new processes and new phenomena, peculiar of the three-level configuration. Those processes and phenomena have stimulated a large attention by the laser spectroscopy and quantum optics

Cascade atom in high-Q cavity: the spectrum for non-Markovian decay

The spontaneous emission spectrum for a three-level cascade configuration atom in a single mode high-Q cavity coupled to a zero temperature reservoir of continuum external modes is determined from the atom–cavity mode master equation using the quantum regression theorem. Initially the atom is in its upper state and the cavity mode empty of photons. Following Glauber, the spectrum is defined via the response of a detector atom. Spectra are calculated for the detector located inside the cavity (case A), outside the cavity end mirror (case B—end emission), or placed for emission out the side of the cavity (case C). The spectra for case A and case B are found to be essentially the same. In all the cases the predicted lineshapes are free of instrumental effects and only due to cavity decay. Spectra are presented for intermediate and strong coupling regime situations (where both atomic transitions are resonant with the cavity frequency), for cases of non-zero cavity detuning, and for cases where the two atomic transition frequencies differ. The spectral features for cases B(A) and C are qualitatively similar, with six spectral peaks for resonance cases and eight for detuned cases. These general features of the spectra can be understood via the dressed atom model. However, case B and C spectra differ in detail, with the latter exhibiting a deep spectral hole at the cavity frequency due to quantum interference effects.

Atom localization via absorption spectrum

We propose a scheme to localize an atom in a three-level A-type configuration inside a classical standing wave field conditioned upon the measurement of frequency of a weak probe field. Inside the classical standing wave field, the interaction between atom and the field is position-dependent due to the Rabi frequency of the driving field; hence, as the absorption frequency of the probe field is measured, the position of an atom inside the classical standing wave field will be determined. Localizing of an atom via absorption spectrum occurs during its motion inside the standing wave field. An investigation of the probe field frequency shows that the degree of localization depends on interaction parameters such as detuning, phase difference between applied fields, and Rabi frequency of the driving field.

A Zero-Voltage and Zero-Current Switching Three-Level DC–DC Converter With Reduced Rectifier Voltage Stress and Soft-Switching-Oriented Optimized Design

A novel zero-voltage zero-current switching (ZVZCS) three-level converter with pulsewidth modulation (PWM) phase-shift control is proposed. The ZCS of the lagging switch is obtained by using a regenerative passive snubber in the secondary. In order to reduce the voltage stress on the rectifier's diodes, a few passive elements are inserted into the primary: a small inductance, two diodes, and a small additional winding of the main transformer. In each half-cycle, one of these diodes will conduct for a short time in order to clamp the voltage of the snubber's capacitor, and thus, the rectifier stress, at (n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sub> /n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> )(V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</sub> /2), n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , and n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> being the transformer's primary and, respectively, secondary turns number. The three-level configuration allows for the reduction of the voltage stress across the power switches to half of the input voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</sub> . The conditions for assuring ZVS of the leading switch and ZCS of the lagging switch are found. Design constraints on the parallel capacitances of the switches of the leading switch, on the snubber's holding capacitor, and on the additional inductance and winding are hence established, allowing for an optimized design of the converter parameters. A dc analysis allows for the calculation of the effective duty cycle, which enjoys a boost effect due to the proposed snubber. Thus, a further reduction of the primary current stress and rectifier voltage stress is obtained. All the improvements conclude in a high efficiency. The influence of the choice of the parameters' values on the regulation capability is pointed out. Experiments on a prototype of 4.5kW confirm the results