Ladder-type Three-level System Research Articles

Influence of phase diffusion on atomic grating in a three-level ladder-type system in lower-level microwave-driven scheme

In this paper, we consider a scheme for electromagnetically induced grating (EIG) in a three-level ladder-type system. A microwave field of finite bandwidth making a standing-wave pattern is applied on lower levels. In addition, we have also introduced an indirect pump in our system. A weak probe field is then applied to study the effects of phase diffusion associated with the microwave control field on EIG. It is found that phase diffusion associated with the strong microwave control field strongly affect the diffraction. We have incorporated the effect of different system parameters such as the strength of the microwave field, indirect pumping mechanism, interaction length, and detuning in the weak probe field. Interestingly, the stronger microwave control field retrieves the loss in diffraction intensity caused by the phase diffusion. Our results show that the introduction of detuning in the optical probe field results in the enhancement of the phase grating effect. Furthermore, our results show that an optimized indirect pump field can slightly improve the first-order diffraction intensities both in the absence and presence of phase diffusion.

Dynamical propagation and all-optical switching in a ladder-type three-level system under the influence of spontaneously generated coherence

We investigate the dynamical of pulse propagation and all-optical switching via a spontaneously generated coherence (SGC) in a three-level ladder-type atomic medium driven by a coupling field under the presence of incoherent pumping. Results show that the SGC causes modulations at the leading edge of the pulse envelope shape. These modulations increase with the together growth of SGC and distance. Furthermore, it is shown that the continuous-wave input probe field is switched ON or OFF by periodically modulating the coupling field. The spontaneously generated coherence has a strong effect on switching efficiency and switching pulse shape. The proposed scheme may have applications in the design of optical switching and optical gain devices in optical telecommunications.

Tailoring solid-state single-photon sources with stimulated emissions.

The coherent interaction of electromagnetic fields with solid-state two-level systems can yield deterministic quantum light sources for photonic quantum technologies. To date, the performance of semiconductor single-photon sources based on three-level systems is limited mainly due to a lack of high photon indistinguishability. Here we tailor the cavity-enhanced spontaneous emission from a ladder-type three-level system in a single epitaxial quantum dot through stimulated emission. After populating the biexciton (XX) of the quantum dot through two-photon resonant excitation, we use another laser pulse to selectively depopulate the XX state into an exciton (X) state with a predefined polarization. The stimulated XX-X emission modifies the X decay dynamics and improves the characteristics of a polarized single-photon source, such as a source brightness of 0.030(2), a single-photon purity of 0.998(1) and an indistinguishability of 0.926(4). Our method can be readily applied to existing quantum dot single-photon sources and expands the capabilities of three-level systems for advanced quantum photonic functionalities.

Effects of finite bandwidth on atomic grating in a three level ladder type system

In this paper, we study the atomic grating produced by a three-level ladder type system which interacts with a strong standing microwave drive field of finite bandwidth. The upper levels of the atoms are coupled by the drive field while the probe field is applied on the lower two levels. We find that in the presence of phase fluctuations associated with the microwave drive field, the diffraction intensities are significantly affected. Our results show that if the probe and microwave drive are on resonance with their respective atomic transitions, then the diffraction intensities can be improved by properly adjusting the strength of the drive field. However, if the probe field is detuned from the resonance, then the diffraction intensities can be improved by appropriately selecting the strength of the drive field, probe detuning and interaction length of the medium. Interestingly, our results also show that the effects of phase grating can also be enhanced by a pertinent choice of various parameters even in the presence of phase diffusion. This results in the suppression of the zeroth order intensity while the first order intensity is increased.

Population distribution in three-level electromagnetically induced transparent system

The interaction between light and matter can be described by the theory of density matrix equations. Based on the theory, the population distribution in a ladder type three-level system under the driven of two laser fields is simulated analytically. It is found that as tuning the frequency of the probe field, the variation of population in the upper level (labeled 2) of probe absorption transition is similar to the one of probe absorption. When the phenomenon of electromagnetically induced transparency (EIT) occurs, there is no population in level 2 at the resonant frequency. This is attributed to the fact that the population in the upper level of absorption transition is related to the absorption cross section closely. The magnitude of the peak of both population and probe absorption are independent of the intensity of the coupling field. Although there is no population in level 2 as full EIT occur, but atoms distributed in the ground level (labeled 1) can be excited to the highest one (labeled 3) in the manner of two-photon resonant absorption by absorbing the probe and the coupling photons. Thus there is obvious population in level 3, and population inversion is formed between level 3 and level 2. This can be used to realize light amplification. Increasing the intensity of the probe field, the population of level 2 grows gradually until it is saturated, while the magnitude of probe absorption will undergoes a process of increase first and then decrease.

Transient amplification without population inversion in a two-field-driven ladder-type three-level system

In this paper, the transient absorption and particle population in a two-field-driven ladder-type three energy level atomic system is simulated numerically with the density matrix equations which describe the interaction of photon and material. It is found that under the radiation of strong coupling and weak probe fields, the probe absorption shows the character of damped oscillation from the time of laser being switched on to the steady state, which presents phenomenon of full transparency. There exists negative absorption during the variation process. But most of the population is on the ground state energy level all the time. This indicates that amplification without population inversion appears during the course of transparency formation. The driving of the coupling field will produce a time-dependent coherent term. Analyzing the variation of both of the population distribution and coherent term with time, it is found that transient amplification without inversion originates from the quantum interference which is related with coupling field. Thus amplification without inversion can be obtained by controlling the intensity of laser fields and the time for laser interaction.

Noise transfer characteristics of Rydberg electromagnetically induced transparency

The transfer mechanism from the amplitude noise of the coupling light to the phase noise of the probe light in a Rydberg electromagnetic induced transparency effect derived from a ladder-type system including 6S1/2↔6P3/2↔62D5/2 of Cs atoms is demonstrated by using Mach-Zehnder interferometer and balanced homodyne detection technology. In our experiments, the transmission signal of 852 nm probe light is measured by scanning the coupling light frequency nearby the transition from 6P3/2 to 62D5/2 Rydberg state, while the frequency of the probe light is locked at the resonance transition of the 6S1/2↔6P3/2. The relative phase stability of two arms of Mach-Zehnder interferometer, which is constructed with the first order diffraction light of probe light through an acoustic-optic modulator, is accomplished by the controlled piezoelectric ceramic with the PID feedback loop. The interferences between the probe light and the reference light of Mach-Zehnder interferometer under the different relative phases are observed. The interference spectrum of probe light is in good agreement with the theoretical simulation result of the ladder-type three-level system. Therefore, we study the transfer characteristics from the frequency noise of coupling light to the phase noise of probe light when coupling light frequency resonance happens at the transition 6P3/2↔62D5/2. We find the significant suppression of the phase noise of probe light at the higher frequency noise. Moreover, we observe the characteristics of the phase noise of the probe light varying with the power of the coupling light under the different detuning degrees of coupling light. In the red detuning side, the transferred phase noise of probe light decreases with the increase of coupling light power, which is different significantly from the scenario under the blue detuning condition. The ions produced in the ionization process of Rydberg atoms will form the local electric field that would cause the energy level of Rydberg states to shift. The investigation of the noise transfer between the coupling light and probe light in the Rydberg electromagnetically induced transparency effect is important for understanding the coherence mechanism of ladder-type system and the some potential applications, such as in Rydberg-atom-based electric field metrology.

Effect of thermal motion on the phenomenon of electromagnetically induced transparency

Atoms and molecules are always in random thermal motion, especially in gas system. This paper investigated the effect of thermal motion on Electromagnetically induced transparency (EIT). During this course, we adopt the theory of density matrix equation for the description of a ladder-type three-level system. The results showed that thermal motion will influence the appearance of EIT greatly and makes EIT is relate to temperature further. An obvious transparent window can be observed only when the temperature is less than 50K. With the increase of temperature, the depth of EIT window decreases quickly until to disappear. At room temperature, we can only see the double peaks of Aulter-Townes with strong coupling field. In addition, we have also observed an interesting phenomenon that with the increase of frequency detuning of the coupling field, the peak that is away from the resonant frequency will develop into an ultra narrow one. Thermal motion will make this narrow peak disappear. Just then, the height of the whole absorption profile increases and the line width of it decreases with the increase of frequency detuning.

Electric field effect on the impurity-related electromagnetically induced transparency in a quantum disk under non-resonant, intense laser radiation

By considering a three-level ladder-type system under electromagnetically induced transparency, the absorption and dispersion of the probe field in a GaAs disk-like quantum dot under simultaneous action of the electric field and non-resonant, intense laser radiation are investigated. We found that some characteristics such as the width of the transmission window and group velocity can be efficiently manipulated by tuning the control field intensity, non-resonant radiation amplitude and electric field strength. Our results may be relevant for future investigations of the optical process in semiconductor quantum structures and for the technological applications in solid- state optoelectronics.

Noise correlations controlled by dressed suppression and enhancement

The intensity noise correlations between anti-Stokes and Stokes fields, generated from spontaneous parametric four-wave mixing (SP-FWM) process have been investigated in a ladder-type three-level system of sodium atomic vapor. By introduction of an external dressing field, the strengthened (weakened) correlations are obtained under enhancement (suppression) condition of SP-FWM. Besides, sharp correlations have been obtained as attributed to a pair of non-classical beams generated from amplified spontaneous emission.

High Refractive Index without Absorption in a Ladder-Type System

A three-level ladder-type system with vacuum-induced coherence and incoherent pumping is studied to obtain a high refractive index without absorption. It is shown that the enhancement of the refractive index without absorption can be accomplished by choosing the proper values of the incoherent pumping, the angle between the two dipole moments, the probe detuning and the relative phase of the two coherent fields.

Multidressing interaction of four-wave mixing image in three-level atomic system

We demonstrate different dressed processes of four-wave mixing (FWM), as changing the powers of the probe, pump, and dressing fields, respectively, in ladder-type three-level system. It is demonstrated that scanning detuning of the dressing field can lead to the direct detection of the dressing effects and the interaction between the dressing fields, compared with scanning that of the probe field. Moreover, by respectively controlling the powers of the dressing, pump, and probe fields, the enhancement and suppression of FWM signals can be switched sensitively. Meanwhile, the spatial splitting in y direction of FWM signal due to the cross-phase modulation and electromagnetically induced gratings is observed, respectively. Such nonlinear signal with switchable enhancement has potential applications in optical switching, optical communication, and quantum information processing.

Electromagnetically induced absorption via incoherent collisions

We conduct theoretical studies on electromagnetically induced absorption via incoherent collisions in an inhomogeneously broadened ladder-type three-level system with the density-matrix approach. The effects of the collision-induced coherence decay rates as well as the probe laser field intensity on the probe field absorption are examined. It is shown that with the increase of the collisional decay rates in a moderate range, a narrow dip due to electromagnetically induced transparency superimposed on the Doppler-broadened absorption background can be turned into a narrow peak under the conditions that the probe field intensity is not very weak as compared to the pump field, which results from the enhancement of constructive interference and suppression of destructive interference between one-photon and multiphoton transition pathways. The physical origin of the collision-assisted electromagnetically induced absorption is analyzed with a power-series solution of the density-matrix equations.

Sub- and superluminance with gain in a three-level ladder-type atomic system with spontaneously generated coherence

The effects of spontaneously generated coherence (SGC) on the propagation of a weak probe pulse are investigated in a ladder-type atomic system. Due to SGC, the properties of the dispersion and the absorption of a three-level ladder-type system are changed greatly. With proper parameters, the system can produce normal and anomalous dispersion regions in the gain region. The effects of the incoherent pumping and the relative phase on the group velocity are also studied. They all can be used as switches to manipulate the group velocity of the weak probe field from gain-assisted sub- to superluminance.

Gain-assisted sub- and super-luminal in a ladder atomic system

With the occurrence of an incoherent pumping field, the properties of the dispersion and the absorption of a three-level ladder-type system are changed greatly. With proper parameters, the system can produce normal and anomalous dispersion regions in the gain region. The existence of the incoherent pumping is the cause for these phenomena, and it can be a knob to manipulate the group velocity of a weak probe field from sub-luminal to super-luminal.

Effects of spontaneously induced coherence on absorption of a ladder-type atom

This paper investigates the effects of spontaneously induced coherence on absorption properties in a nearly equispaced three-level ladder-type system driven by two coherent fields. It find that the absorption properties of this system with the probe field applied on the lower transition can be significantly modified if this coherence is optimized. In the case of small spontaneous decay rate in the upper excited state, it finds that such coherence does not destroy the electromagnetically induced transparency (EIT). Nevertheless, the absorption peak on both sides of zero detuning and the linewidth of absorption line become larger and narrower than those in the case corresponding to the effects of spontaneously induced coherence; while in the case of large decay rate, it finds that, instead of EIT with low resonant absorption, a sharp absorption peak at resonance appears. That is, electromagnetically induced absorption in the nearly equispaced ladder-type system can occur due to such coherent effects.

Optical bistability in a three-level semiconductor quantum-well system

Optical bistable behavior in a unidirectional ring cavity (or a Fabry–Perot cavity) containing a semiconductor quantum well, described as a three-level ladder-type system with similar transition energies, has been studied. The system interacts with a strong driving field which is in two-photon resonance with the intersubband transition and thus simultaneously drives all three levels into phase-locked quantum coherence. The threshold for switching to upper branch of the bistable curve is found to be reduced due to the presence of quantum interference. Such system can be used for making efficient and fast all-optical switching devices.

Observation of an electromagnetically induced change of absorption in multilevel rubidium atoms.

A 64.4% reduction in absorption at the rubidium D2 line is observed when a pumping field at 775.8 nm is tuned on resonance to the transition between the excited states 5${\mathit{P}}_{3/2}$ and 5${\mathit{D}}_{5/2}$. As the pumping field is tuned off resonance, an absorption peak appears at the side of the Doppler-broadened D2 line. This modification in absorption is related to pumping-induced atomic coherence in this three-level ladder-type system. This experiment is done in a Rb vapor cell at room temperature and with cw diode lasers for both pumping and probe beams in a Doppler-free configuration.