Four-level Atomic System Research Articles

Magneto-optical rotation of surface plasmon polaritons

We investigate magneto-optical rotation (MOR) of surface plasmon polaritons (SPPs) at the interface of a metal and a four-level atomic system. The MOR of SPPs can be controlled and modified with the intensity and frequency of the applied fields. We show the birefringence enhancement of the weak probe fields propagating through the atomic medium in the presence of the static magnetic field. The external magnetic field has a vital role in the generation and control over the MOR of SPPs. The MOR completely stops when either the external magnetic field or the probe field or both are tuned to resonance. A pretty behavior of MOR of SPPs is observed for a specific set of control field frequency. The enhanced MOR of SPP has significant applications in atomic spectroscopy, optical communication, nano-photonics, optical switches, and precise measurement.

Microwave-assisted all-optical switching in a four-level atomic system

We study the all-optical switching of the weak probe field via a four-level atom system with the help of a microwave field and electromagnetically induced transparency effect. Here, the microwave field is used for coupling two-folded lower levels to which double dark resonances (DDRs) can arise. The atomic medium is switched from transparent to complete absorption under the DDRs. It is shown that the absorption spectrum, pulse propagations and all-optical switching dynamics of the probe field are dependent on the intensity of the microwave field, applied fields and probe detuning. Furthermore, the switching mode between the probe field and the microwave field can be antisynchronous or synchronous, depending on the probe detuning being adjusted to be equal to zero or ± $$\Omega _{{c}}$$ , respectively. Our results possibly are helpful in actual tests to design all-optical switching and optical storage devices in optical communications and signal processing.

Enhanced cross-Kerr nonlinearity induced -symmetry in optical lattices

We propose a physical scheme to realize optical lattices that are symmetric under a combination of parity and time () reversal. The -symmetric structures can be constructed with periodical gain and loss profiles in a coherently prepared four-level N-type atomic system under the effects of cross-Kerr nonlinearity and Doppler broadening. The atoms are considered in the Gaussian density distribution loaded into the dipole traps of one- and two-dimensional optical lattices. The spatial modulation of the probe field susceptibility is achieved by a proper combination of standing wave strong control fields. With proper detunings and coupling field Rabi frequencies, we find the conditions of achieving -symmetry in optical lattices of nonlinear atoms. We show that the -symmetry can be realized when the cross-Kerr nonlinearity is significantly enhanced, and further demonstrate that it survives the Doppler broadening. Our model is based on experimentally observable and effectively controllable scheme which may find potential applications in optical information processing.

High-precision three-dimensional Rydberg atom localization in a four-level atomic system* *Project supported by the National R&D Program of China (Grant No. 2017YFA0304203), the National Natural Science Foundation of China (Grant Nos. 61875112, 61705122, 62075121, and 91736209), the Program for Sanjin Scholars of Shanxi Province, the Key Research and Development Program of Shanxi Province for International Cooperation (Grant No. 201803D421034), Shanxi

Rydberg atoms have been widely investigated due to their large size, long radiative lifetime, huge polarizability and strong dipole-dipole interactions. The position information of Rydberg atoms provides more possibilities for quantum optics research, which can be obtained under the localization method. We study the behavior of three-dimensional (3D) Rydberg atom localization in a four-level configuration with the measurement of the spatial optical absorption. The atomic localization precision depends strongly on the detuning and Rabi frequency of the involved laser fields. A 100% probability of finding the Rydberg atom at a specific 3D position is achieved with precision of ∼0.031λ. This work demonstrates the possibility for achieving the 3D atom localization of the Rydberg atom in the experiment.

Improvement of Microwave Electric Field Measurement Sensitivity via Multi-Carrier Modulation in Rydberg Atoms

The microwave electric field intensity is precisely measured by the Autler–Townes splitting of electromagnetically induced transparency spectrum in a 5S1/2−5P3/2−57D5/2−58P3/2 four-level ladder-type 85Rb atomic system. A robust multi-carrier modulation scheme is employed to improve the spectral signal-to-noise ratio, which determines the optical readout of Rydberg atom-based microwave electrometry. As a result, a factor of 2 measurement sensitivity improvement is clearly achieved compared with the on resonant Autler–Townes splitting case credit to the advantage of matched filtering. This research paves the way for building a high sensitivity, portable sensor and offers a platform for achieving compact and sensitive receiver.

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.

Controllable two- and three-dimensional atom localization via spontaneously generated coherence

A scheme for two-dimensional (2D) and three-dimensional (3D) atom localization in a four-level N-type atomic system is proposed. The scheme is based on the probe absorption measurement when the atom passes through the orthogonal standing-wave fields. Using the electromagnetically induced transparency, we prove that the probe field absorption is spatially localized in sub-wavelength domain. We also show that the spatial resolution of 2D and 3D atom localization strongly depends on the probe field detuning, the quantum interference parameters induced by spontaneous emission, and the relative phase between the driving fields.

Propagating multi-channel four-wave mixing process in the modulated moving photonic band gap.

Three and four electromagnetically induced transparency windows generate the multi-channel four-wave mixing (FWM) process are observed in a four-level atomic system. The transmission of the probe field and the reflection of the FWM are investigated in the modulated moving photonic band gap structures which are caused by the coupling fields with a relative small detuning offset when scanning detuning frequency of the probe field and the dressing field, respectively. The experimental results show that the more channels spectrum signal of the FWM process can be modulated and the generated multi-channel can be further modulated by adding a dressing field. We have also explained theoretically these experimental results which may have applications in the design of photonic crystal and optical signal amplifiers.

Multi-wave-mixing-induced nonlinear modulation of diffraction peaks in an opto-atomic grating

We propose an atomic model in close-loop configuration, which exhibits controllable symmetric and asymmetric evolution of significantly enhanced diffraction peaks of the weak probe beam in an opto-atomic grating at far-field regime. Such results are obtained by the linear and nonlinear modulation of the intensities of the diffraction peaks as a result of multi-wave-mixing-induced modification of spatially modulated coherence in a closed four-level atomic system. Novelty of the results lies in predicting the diffraction pattern with uniform peak height due to the dominance of the amplitude part of the grating-transfer-function at the condition of exact atom-field resonance, which is unique to the present model. Efficacy of the present scheme is to apply it in producing nonlinear light generated by four-wave-mixing-induced control of spatially modulated coherence effect. The work also finds its importance for its applicability in the field of all-optical devices.

High-dimensional atomic microscopy in surface plasmon polaritons* *Project supported by CAS-TWAS Presidential fellowship and Chinese Scholarship Council (CSC) fellowship.

We develop a new scheme of two-dimensional (2D) and three-dimensional (3D) atom localization via absorption and gain spectra of surface plasmon polaritons (SPPs) in a closed loop four-level atomic system. For the atom–field interaction, we construct a spatially dependent field by superimposing two (three) standing-wave fields (SWFs) in 2D (3D) atom localization, respectively. We achieve high-precision and high spatial resolution of an atom localization by appropriately adjusting the system parameters such as probe field detuning and phase shifts of the SWFs. The absorption and gain spectra are used to attain information about the position of an atom in SPPs. Our proposed scheme opens up a fascinating way to improve the atom localization that supplies some practical applications in a high-dimensional SPPs.

Control of space-dependent four-wave mixing in a four-level atomic system

We propose a scheme to demonstrate the manipulation of space-dependent four-wave mixing (FWM) in a four-level atomic system. By adjusting the detuning of the control field, one can effectively control the FWM output field transferred from a pump beam carrying orbital angular momentum. More interestingly, by appropriate choice of the intensity of the control field, the FWM field can be significantly enhanced and phase twist is almost completely suppressed. Furthermore, the superposition modes created by the interference between the FWM field and a same-frequency Gaussian beam are also discussed, showing many interesting properties. Our results may open some possibilities for phase imprinting in Bose-Einstein condensates or atom manipulation with optical tweezers.

High-precision three dimensional atom localization via multiphoton quantum destructive interference.

We propose an effective scheme for high-precision three dimensional(3D) atom localization via measuring the population of excited state in a four-level atomic system driven by a probe field and three orthogonal standing-wave fields. In this scheme, the position-dependent multiphoton quantum destructive interference leads to multiphoton excitation of the excited state and enhances the fluorescence emission. We show that adjusting the frequency detuning and phase shifts associated with the standing-wave fields can modify the multiphoton quantum destructive interference and lead to a redistribution of the atoms. The maximal probability of finding the atom at the certain position in one period of the standing-wave fields can be 100% and the highest spatial precision is about 0.02λ.

A tunable broadband microwave absorber based on coherent population trapping

A scheme is proposed for a tunable broadband microwave absorber using a four-level Rydberg atom system with competition between electromagnetically induced transparency (EIT) and coherent population trapping (CPT). Two laser fields drive the Rydberg atoms from the ground state to a Rydberg state, forming a cascade-type EIT/CPT system. When a microwave (MW) field couples the Rydberg transition, a strong MW absorption peak appears. A narrow band MW absorber could be obtained via EIT, however, using CPT, the MW absorption spectrum can be significantly broadened and enhanced to have a bandwidth about ten times larger than that obtained with EIT and whose peak value can also be enhanced by a factor of ten, based on simulation.

Precision in two-and three-dimensional atom localization via detuning and phase shifts using four-level tripod atomic system

The high-precision position measurement scheme of a single atom in two-dimensions and three-dimensions is investigated in a four-level tripod-type system. The atom interacts with the two orthogonal standing wave fields (OSWFs) and three OSWFs for two- and three-dimensional (2D, 3D) atom localization. The high-precision position of the atom is observed by adjusting the suitable system parameters. We achieve a high-precision single localized peak in the 2D plane and a single localized sphere smaller than the cubic optical wavelength in 3D volume space. We also see the impact of the Doppler shift on atom localization in 2D and 3D. We show that the Doppler shift dramatically deteriorates the precision of spatial information. The proposed high-precision atom localization scheme has applications in laser cooling and Bose–Einstein condensation phenomena.

Azimuthal modulation of probe absorption and transfer of optical vortices

We analyze azimuthal modulation of probe field absorption profile in a closed four-level inverted Y-type atomic system. We employ a Laguerre–Gaussian beam and a microwave field to realize spatially varying atomic susceptibility, which is responsible for the generation of structured light. An extra nonvortex control beam is used to ensure electromagnetically induced transparency at the core of Laguerre–Gaussian beam. Our proposed model exhibits both absorption and gain at different azimuthal angles, and orbital angular momentum of light can be identified via absorption profile of the probe field. We further discuss the transfer of optical vortices from Laguerre–Gaussian beam to the transmitted probe field.

Kerr-nonlinearity-modulated dressed vortex four-wave mixing from photonic band gap

Considering the fact that the orbital angular momentum of light can be transferred through light-matter interactions, we experimentally induced a dressed vortex four-wave mixing (FWM) with the interaction between a vortex probe beam and an inverted Y-type four-level atomic system with a photonic band gap. Further, the Kerr-nonlinearity-modulated propagation behaviors of the probe and the dressed FWM vortices are investigated, including the spatial shift, splitting, and incompleteness of the vortex shape. Strikingly, the propagation behaviors of the vortex beams can be influenced by the interaction between the nonlinear phase and the spiral phase. This study would promote the development of optical computing and information processing science related to the interactions between optical vortices and samples.

Two-dimensional atom localization via a combination of the standing-wave and Gaussian fields

The localization of atom is studied in two-dimensional (2D) in a four-level V-type atomic system by using the Gaussian field. The atom localization is investigated through the absorption spectrum of the weak probe field inside two orthogonal standing-wave fields. We consider three hypotheses for the interaction between the atom and fields (standing-wave and Gaussian fields), each hypothesis is considered individually. We obtain the expression for the first-order approximation of the absorption of the probe field mathematically for the hypothesis (I). The Gaussian field parameter plays an important role in the precision of the atom localization. The 2D atom localization can be dependent on the detuning of the probe field (resonance and off-resonance), the Rabi frequencies and the phase shifts.

Electromagnetically induced transparency and electromagnetically induced absorption in Y-type system

The propagation of a probe field through a four-level Y-type atomic system is described in the presence of two additional coherent radiation fields, namely, the control field and the coupling field. An expression for the probe response is derived analytically from the optical Bloch equations under steady state condition to study the absorptive properties of the system under probe field propagation through an ensemble of stationary atoms as well as in a Doppler broadened atomic vapor medium. The most striking result is the conversion of electromagnetically induced transparency (EIT) into electromagnetically induced absorption (EIA) as we start switching from weak probe regime to strong probe regime. The dependence of this conversion on residual Doppler averaging due to wavelength mismatch is also shown by choosing the coupling transition as a Rydberg transition.

Efficient Images Storage Due to a Microwave Field in a Cold Four-Level Atomic System

Quantum memories that are able to store arbitrary two-dimensional images offer advantages over light pulses memories, in terms of both speed and capacity. In this work, we propose an efficient scheme to realize the storage and retrieval of images in a four-level quasi-Λ system of cold atoms. This scheme relies on the cross-phase modulation controlled by an employed intensity dependent microwave field during the storage time. Both theoretical analysis and numerical simulation clearly show that the microwave field can effectively modify the spin coherence and improve the visibility of the reconstructed images with low nonlinear absorption. The phase shift and energy retrieving rate of the probe field are immune to the coupling field and the atomic optical density. Compared to the existing scheme, the maximum advantage of this one is that the energy loss in this process is reduced markedly. This work provides an alternative way for efficiently enhancing the performance of EIT based light-storage devices for all-optical quantum information processing.

Polarization independent double-band electromagnetically induced transparency effect in terahertz metamaterials

In this article, we experimentally and numerically investigated a metamaterial (MM) geometry capable of exhibiting polarization independent double-band electromagnetic induced transparency (EIT) effect. The meta-molecule unit of the proposed MM configuration composed of a strip and two asymmetric split ring resonators (SRRs). For polarization independent double-band EIT effect, the existing meta-molecule unit is converted into a cross-like structure adorned with four SRRs. Terahertz transmission response is analyzed for two orthogonal polarization directions of the incident light to confirm the polarization independent response. In order to understand and explain our numerical findings more elaborately we have employed four-level tripod atomic system based analytical model. The transmission response is also analyzed for different angle of incidence of the two orthogonal polarizations. In order to demonstrate the practical applicability of our study, we have studied the effect of transmission with the change of refractive index of analyte of thickness 10 μm coated on the top of the MM resonators. The calculated sensitivities for the 1st, 2nd and 3rd dips are 121 GHz/RIU, 138 GHz/RIU and 135 GHz/RIU (RIU, refractive index unit) respectively. Our study can also play an important role in the advancement of slow light devices, modulators and filters.