Sub-half-wavelength atom localization via probe absorption spectrum in a four-level atomic system

We present a simple scheme of atom localization in a subwavelength domain via manipulation of probe absorption spectrum in a four-level atomic system. By applying two orthogonal standing-wave fields, the localization peak position and number as well as the conditional position probability can be controlled by the intensities and detunings of optical fields, and the sub-half-wavelength atom localization is also observed. More importantly, there is 100% detecting probability of the atom in the subwavelength domain when the corresponding conditions are satisfied.     

Sub-half-wavelength atom localization via bichromatic phase control of spontaneous emission

We show that the bichromatic phase control of the spontaneous emission spectrum leads to the sub-half-wavelength atom localization. We consider a three-level Λ-type atom interacting with a bichromatic coupling field and a bichromatic probe field with equal frequency difference. One component of the bichromatic coupling field is a standing-wave field with position dependent Rabi frequency. When the spontaneous emitted photons are detected, the atom is localized in either of the two half-wavelength regions with 50% probability by the variation of the difference between the relative phases of the two bichromatic fields.     

Efficient two-dimensional atom localization via spontaneous emission in a single decay channel

We investigate the two-dimensional atom localization behaviors in a four-level atomic system via controlled spontaneous emission in a single decay channel. It is found that the detecting probability and precision of atom localization behaviors can be significantly improved via adjusting the system parameters. More importantly, the two-dimensional atom localization patterns reveal that the maximal probability of finding an atom within the sub-half-wavelength domain of the standing waves can reach unity when the corresponding conditions are satisfied. As a result, our scheme may be helpful in laser cooling or the atom nano-lithography via atom localization.     

Coherent control of narrow structures in absorption,transparency and dispersion by interference induced among the Rabi-split resonances

The evolution of nonlinear behaviour of electromagnetically induced absorption and transparency subject to coherent perturbation, is presented in a triply driven five-level atomic system. It has been shown that the coherence effects like absolute line narrowing, single or multiple transparencies, sharply varying dispersion and two opposite types of quantum switching can be efficiently controlled by interference induced among the Rabi-split resonances at various situations. As far as measurement induced subwavelength atom localization is concerned, this model can be very much useful in controlling single peak atom localization in subwavelength and sub-half-wavelength domain by three different ways.     

Spatial-dependent probe transmission based high-precision two-dimensional atomic localization

Herein, we propose a scheme for the realization of two-dimensional atomic localization in aλ-type three-level atomic medium such that the atom interacts with the two orthogonal standing-wave fields and a probe field. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be obtained by monitoring the probe transmission spectra of the weak probe field for the first time. A single and double sharp localized peaks are observed in the one-wavelength domain. We have theoretically archived high-resolution and high-precision atomic localization within a region smaller thanλ/25×λ/25. The results may have potential applications in the field of nano-lithography and advance laser cooling technology.     

Atom localization of a two-level pump-probe system via the absorption spectrum

We propose a scheme to localize a two-level atom inside a classical standing wave field conditioned upon the measurement of the frequency of a weak probe field at resonance excitation of a two-level atomic system. Inside the classical standing wave field, the interaction between the 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. The effects of atomic parameters on atom localization are then discussed.     

Generation of sub-half-wavelength micro-optical traps by dichroic evanescent standing waves

The bi-dimensional optical lattices formed by several sets of laser evanescent standing waves propagating at the surface of a dielectric prism are investigated. The characteristics of the optical traps including their depths and the sizes are analysed. It is shown that the micro-optical lattice with a sub-half-wavelength size can be achieved by the interference of the selected evanescent waves. The scheme together with the recently developed atomic chip may be used for atomic quantum manipulation.     

High-precision two-dimensional atom localization via probe absorption in an M-scheme atomic system

In the present paper, we investigate the behavior of two-dimensional atom localization in a five-level M-scheme atomic system driven by two orthogonal standing-wave fields. We find that the precision and resolution of the atom localization depends on the probe field detuning significantly. And because of the effect of the microwave field, an atom can be located at a particular position via adjusting the system parameters.     

Two-dimensional atom localization via probe absorption in a four-level atomic system

We have investigated the two-dimensional (2D) atom localization via probe absorption in a coherently driven four-level atomic system by means of a radio-frequency field driving a hyperfine transition. It is found that the detecting probability and precision of 2D atom localization can be significantly improved via adjusting the system parameters. As a result, our scheme may be helpful in laser cooling or the atom nano-lithography via atom localization.     

Efficient two-dimensional atom localization via phase-sensitive absorption spectrum in a radio-frequency-driven four-level atomic system

A scheme of two-dimensional (2D) atom localization based on the phase-sensitive probe absorption is proposed in a four-level Λ-type atomic system with an assisting radio-frequency (rf)-driven field. The obtained 2D atom localization patterns reveal that the maximal probability of finding an atom within the sub-wavelength domain of the standing waves can arrive at unity by appropriate choice of the system parameters.     

Atom Localization Using a Rydberg State

A theoretical study is presented for two-dimensional (2D) and three-dimensional (3D) atom localization in a four-level atomic system involving a Rydberg state. The scheme is based on a mixture of two well-known V- and ladder-type systems illuminated by a weak probe field as well as control and switching laser beams of larger intensity, which could be standing waves. As a result of space-dependent atom? light interaction and due to the effect of Rydberg electromagnetically induced transparency or Rydberg electromagnetically induced absorption, various 2D and 3D localization structures appear. Specifically, the detecting probability and precision of 2D and 3D atom localization can be remarkably enhanced through suitable adjusting the controlling parameters of the system. The proposed scheme may provide a promising approach to achieve high precision and perfect resolution 2D and 3D atom localization.     

Microwave-Controlled Light-Pulse Propagation in a Driven Λ-Type Atomic System with Two-Folded Levels

The temporal and spatial dynamics of one weak probe laser pulse, propagating through a Λ-type atomic medium with two-folded levels under the resonant excitation of one microwave driving field and one strong control field, is investigated in this paper. By numerically solving coupled Bloch-Maxwell equations, it isfound that, in the absence of the microwave driving field, the atomic medium is transparent to the probe pulse at line center, which propagates over sufficiently long distances. By contrast, when the microwave driving field is applied, the probe pulse at line center can be rapidly absorbed on propagation. This substantial reduction of probe transmittance caused by the microwave driving field may lead to potential applications in designing a new kind of optical switching.     

Transient absorption–dispersion properties of four-level atomic system via elliptically polarized probe light and magnetic field

A novel four-level atomic system which interacted by an elliptically polarized probe field and a control laser field in the presence of external magnetic field is proposed. Here, we are interested in the transient properties of a weak probe field due to its potential application on quantum computing and quantum communication. It is shown that the external magnetic field and relative phase between two electric field components of the probe field can influence the probe absorption and dispersion.     

基于量子相干控制吸收的准Λ型四能级原子局域化研究

提出了一种基于量子相干控制吸收的对准Λ型四能级原子进行二维局域化方案. 利用密度矩阵微扰理论, 得到了确定原子空间位置信息的筛选函数解析表达式. 在缀饰态表象中, 分析了在相干控制场作用下原子初始状态对原子局域的影响. 数值模拟了控制场参量对原子局域化结果的影响. 研究发现原子局域化结果与初始时刻在控制场作用下原子在下能态的布局、下能级间产生的极化密切相关; 不管探测场与耦合场是否满足电磁感应透明配置条件, 通过改变控制场中的行波场的振幅和探测场的失谐量, 均可实现高精度原子局域化, 在亚波长范围内测量到原子的概率达到100%.     

电磁诱导光透明过程中的Wigner-Yanse偏振信息

利用约化密度矩阵及信息的定义,研究了电磁诱导光透明机理下, 控制场变化过程中探测场与原子系综的Wigner-Yanse偏振信息, 结果表明:探测场信息转移过程中,原子的信息量不仅依赖于光子的数目及光子的状态, 还依赖于系综内原子的数目;调节控制场,使探测场不能通过介质时,探测场完成信息转移, 原子系综内单个原子信息量获得最大值,但探测场的信息量并没有完全地转移到原子系综. 关键词： 电磁诱导光透明 暗态极化子 Wigner-Yanse偏振信息     

Negative refraction without absorption via both coherent and incoherent fields in a four-level left-handed atomic system

This paper attempts a probe into negative refraction without absorption by means of an incoherent pump field and a strong coherent field coupling the dense four-level atomic system. With the application of the incoherent pump field to manipulate the populations in atomic levels and the variable strong coherent field to create quantum coherence, the constraint condition of two equal transition frequencies responding to the probe field in the atomic system isn't required. And these lead to the propagation transparency and strong magnetic response of the probe field, left-handedness with vanishing absorption in the atomic system. However, an excessive coherent field intensity would increase the absorption.     

Atom localization in a four-level atomic system with an assisting radio-frequency driven field

We propose a scheme for atom localization in a four-level atomic system by means of a radio-frequency field driving a hyperfine transition within the two ground states. It is found that, due to the quantum disturbed effect induced by the radio-frequency field, the property of atom localization can be significantly controlled. This scheme shows some characteristics that other schemes of atom localization do not have, which may provide some possibilities for the technological applications in atom nano-lithography.     

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.     

N型四能级系统的原子吸收

研究了在较强光低饱和限制下相干光场与N型四能级原子相互作用系统中原子的吸收性质。借助于数值计算,讨论了较强光失谐、探针光强、激发能级向低能级衰减的分配系数对原子吸收的影响。结果表明,抽运场失谐使原子吸收发生横向变化,信号场失谐使原子吸收发生纵向变化;探针光强影响非线性吸收,并通过它影响原子吸收,当探针光强远小于抽运和信号光强时,原子吸收与线性吸收一致,均表现为电磁感应透明特征,当信号光强增大,非线性吸收产生了增益,原子吸收也由透明变为增益;激发能级同时向两个低能级衰减,当对应探针光的原子衰减通道的衰减分配系数趋近零时,原子吸收随该系数变化非常强烈,当该分配系数等于零时,其增益在探针场共振处趋于无穷大。     

Absorption Changes Induced by Off-Resonance Driving a Degenerate Two-Level System

The alteration of atomic absorption via quantum coherence is observed in the degenerate two-level atomic system. It is shown that when the detuning of coupling field equals to that of probe light, i.e. two-photon resonance, the reduction of atomic absorption via electromagnetically induced transparency occurs. However, when we tune the coupling field to two-photon off-resonance, the enhancement of absorption is obtained for the probe field. The influences of one-photon detuning and intensity of coupling field on absorption are also experimentally demonstrated.