Dynamic generation of beating signals in an atomic system with a static magnetic field

In an \(F_{e}=0\,\leftrightarrow \,F_{g}=1\) transition, which interacting with a weak \(\pi \) -polarized probe field and a strong \(\sigma \) -polarized coupling field, we obtain the controlled beating signals depending on the applied magnetic field. In this configuration, we devise a procedure of light storage and retrieval where the magnetic field is switched off in the storage stage, but the magnetic field is switched on in the retrieval stage. Therefore, the beating signals is generated in the retrieval stage, which exhibits a series of maxima and minima in intensity. In addition, we can obtain two fast optical precursors and slow beating singals when the incident probe field is a squared pulse.     

Dynamic control of photonic bandgap mediated by vacuum-induced coherence

We theoretically examine the storage and retrieval of a light pulse in a medium comprised of four-level atoms of the V − Λ-type. The two intermediate levels are probed by a weak field and vacuum-induced coherence effects lead the system to transparency. The temporal variation of the intermediate levels' splitting is used as an external parameter which allows the transfer of the impinging field to a combination of spin coherences. An auxiliary and far-detuned control field in a standing-wave configuration is used to induce a variable photonic bandgap by cross-phase modulation. It is shown that dynamic control of such a bandgap can be used to coherently manipulate the previously stored probe pulse. We use a general scheme to take into account multiwave mixing effects and solve the combined Maxwell-Bloch equations for the relevant coherences. It is shown that the system acts as an all-optical router.     

Transient electron population and optical properties in a semiconductor quantum well

We investigate the transient behaviors of the dispersion and the absorption in a three-level GaAs/AlGaAs semiconductor quantum well system. It is found that the Fano interference and the energy splitting affect the transient behaviors dramatically, which can be used to manipulate efficiently the gain-absorption coefficient and group velocity of the probe field. The dependence of transient electron population on the Fano interference and the energy splitting is also discussed.     

Low-light-level all-optical switching

We propose an all-optical switch that utilizes the technique of storage and retrieval of light pulses. A single photon (probe pulse) switched by another (switching pulse) is feasible, and the on-off ratio can be as large as 10 dB. We have experimentally demonstrated that the energy of the retrieved probe pulse is reduced to about 10% because of the presence of a switching pulse with an energy per unit area of one photon per lambda(2)/(2pi). The achieved result does not depend on the coupling intensity, the atomic optical density, or the width and shape of the switching pulse.     

Coherent control of optical bistability in tunnel-coupled double quantum wells

We analyze optical bistability (OB) behavior based on intersubband transitions in an asymmetric coupled-quantum well (CQW) driven coherently by a probe laser field and a control laser field by means of a unidirectional ring cavity. We demonstrate that OB can be controlled by tuning the energy splitting between two tunnel-coupled electronic levels, the intensity of the control field, and the frequency detuning of the probe and control fields. The influence of the electronic cooperation parameter on the OB behavior is also discussed. This investigation may be used for optimizing and controlling the optical switching process in the CQW solid-state system, which is much more practical than that in atomic system because of its flexible design and the controllable interference strength.     

Tunneling induced transparency and giant Kerr nonlinearity in multiple quantum dot molecules

The linear absorption and the Kerr nonlinearity of multiple quantum dots molecules controlled by the tunneling rather than the laser fields are investigated. The tunneling between the dots can induce multiple transparency windows. By varying the energy splitting of the excited states and the tunneling intensity, the width of the tunneling induced transparency windows can be narrowed. Within the narrowed transparency windows, the steep dispersion profile of the probe field makes it possible to enhance the Kerr nonlinearity. Therefore more than one probe fields with different frequencies can acquire giant Kerr accompanied by vanishing absorption simultaneously.     

Transient gain-absorption of the probe field in asymmetric semiconductor quantum wells

Under the weak-probe approximation, we theoretically investigate the transient gain-absorption property of the probe field in a four-level asymmetric semiconductor quantum well system. We find that the strength of Fano interference and the energy splitting affect the transient gain-absorption property of the weak continuous-wave (CW) probe field or Gaussian-pulse probe field dramatically. The dependence of transient gain-absorption property of the probe field on the intensity and the frequency detuning of the strong coupling field is also given. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength. Thus, it may provide some new possibilities for technological applications.     

Dynamic control of retrieval contrast in a Λ-type atomic system

We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in Λ configuration. The memory procedure consists of write-in, storage, and retrieval phases. By applying a weak microwave field in the storage stage, additional phase-dependent terms are included, and the contrast of the output signal pulses can be dynamically controlled (enhanced or suppressed) through manipulating the relative phase φ between optical and microwave fields. Our numerical analysis shows that the contrast is enhanced to the most extent when φ=1.5π. In addition, the contrast is in proportion to the Rabi frequency of the microwave field with a certain relative phase.     

Electromagnetically induced transparency of single Λ-type three-level atom in high-finesse optical cavity

We study the features of the electromagnetically induced transparency (EIT) in a single Λ-type three-level atom placed in a high finesse cavity under the action of a coupling laser and a probe laser. Our calculations show that three transparency windows appear when the pump strength is big enough. It can be explained by the residual pump in the cavity resulting mostly in the energy splitting. Level |3〉is split into four slightly different energy levels. An interference takes place between excitation pathways. Furthermore, it is also shown that the frequencies of the EIT windows can be tuned by changing the coupling field detuning Δ₂ and the reflection profile is very sensitive to the cavity field detuning Δ_c.     

相干诱导冷原子微腔中的动态光存储

将行波耦合激光、驻波光栅激光和静磁场作用于一个超冷原子系综,获得了由两个Bragg反射区和一个电磁感应透明区构成的动态可控光学微腔。对耦合激光、光栅激光和静磁场进行时间调制,将一个弱探测激光送入这一相干诱导光学微腔,使其形成周期振荡,然后再根据需要在一定时间延迟之后将其导出,将这一伴随着较弱能量损耗的探测脉冲受限传播过程视为一个有效的动态光存储机制。对提出的信息存储机制进行了数值模拟,讨论了它的优点和实用价值,提出了它的发展前景。     

Gradient echo memory in a tripod-like dense atomic medium

We analyze the storage and retrieval of a weak light pulse, having two orthogonally (circularly) polarized components, onto an atomic ensemble of four-level atoms of the tripod type driven by a far detuned coupling field. The atoms are subject to a longitudinal magnetic field which produces a spatially varying Zeeman splitting of the lower levels along the medium and allows for a spatial encoding of the different angular frequencies of the input pulse during the storage phase. A single reversion of the external magnetic field results in a rephasing of the dipoles and leads to the release of the stored signals. The shape of the recovered pulse is a time-reversal copy of the input pulse. The application of an additional reversion of the magnetic field during the storage phase allows the release of a copy of the input pulse without time reversal. We also show that the system may operate like an all-optical multiplexer when considering two impinging optical fields which have orthogonal components. The proposal has potential applications in quantum information processing.     

Where is the energy of slow light stored?

We analyze the energy storage process of light propagating with slow group velocity in a sample where electromagnetically induced transparency (EIT) is created by a strong coupling field. We compare the formation of slow light in EIT and in self-induced transparency (SIT). For SIT, soliton-like propagation of light with essentially reduced group velocity takes place because of the temporary storage of an appreciable part of the pulse energy in the atoms. For EIT, no energy of the probe is stored in the atoms. This energy is transformed to the coupling field and leaves the sample with phase velocity c without absorption. Slow light is formed by a low frequency coherence induced at the input by the probe and coupling fields in a two-quantum excitation process. This coherence propagates as a “spin wave” with small group velocity, and at a large distance from the input, the coherence rules the process of the energy transformation from the coupling field to the probe, reproducing exactly the temporal profile of the probe at the input.     

Long-time-storage mechanism for Tm:YAG in a magnetic field

We obtained a long-time-storage mechanism for spectral features in thulium ions doped into YAG by applying a magnetic field that splits the electronic ground state. We show experimentally that the storage time can be more than 30 s, which is 3 orders of magnitude longer than that of the metastable state that normally is used for information storage in this material. Level splitting and storage lifetimes for various magnetic field strengths of as much as 5 T were investigated. This storage mechanism will be relevant in the many coherent transient-based signal-processing schemes in which Tm:YAG is being used, and we demonstrate long-time storage in a basic data storage application.     

Controllable beating signal using stored light pulse

We experimentally study the controllable generation of a beating signal using stored light pulses based on electromagnetically induced transparency(EIT) in a solid medium. The beating signal relies on an asymmetric procedure of light storage and retrieval. After storing the probe pulse into the spin coherence under the EIT condition, two-color control fields with opposite detunings instead of the initial control field are used to scatter the stored spin coherence. The controllable beating signal is generated due to alternative constructive and destructive interferences in the retrieved signal intensities. The beating of the two-color control fields is mapped into the beating of weak probe fields by using atomic spin coherence. This beating signal will be important in precise atomic spectroscopy and fast quantum limited measurements.     

利用非相干泵浦调控V型三能级系统的吸收与色散

理论研究了V型三能级系统中的吸收与色散特性,证明在探测光几乎无损耗的情况下可以实现超光速和亚光速传输。通过引入一束非相干泵浦场的作用,使输出探测光产生增益,并且在强耦合场诱导的Autler-Townes分裂(AT分裂)的情况下,可以得到探测光脉冲的增益抑制和相应的反常色散。     

近场光学在高密度存储中的应用

近场光学在高密度存储方面有着很大的潜力 ,使得近场光学存储近年来得到了广泛的关注。近场光学存储具有高密度大容量及可以利用许多已有相关技术等优点 ,预计近场光学存储密度能达到 7Gbit/ cm2 ;它还可以采用硬盘驱动器中的空气悬浮磁头技术和磁光存储中的技术等 ,使近场存储的研究和开发更加迅速。目前 ,近场光学存储主要有三种方案 :探针型方案、超分辨率近场结构、固体浸没透镜方案 ,这三种方案都是通过不同的方法缩小记录光斑来实现高密度的存储。介绍了近场光学存储的原理、研究现状及材料 ,并对三种近场存储方案的实现方法和发展概况作了详细的阐述 ,分析了这三种方案的优缺点     

Coherent optical detection of highly excited Rydberg states using electromagnetically induced transparency

We demonstrate coherent optical detection of highly excited Rydberg states (up to n=124) using electromagnetically induced transparency (EIT), providing a direct nondestructive probe of Rydberg energy levels. We show that the EIT spectra allow direct optical detection of electric field transients in the gas phase, and we extend measurements of the fine structure splitting of the nd series up to n=96. Coherent coupling of Rydberg states via EIT could also be used for cross-phase modulation and photon entanglement.     

静电场作用下双势阱分子隧道效应的猝灭及能级裂距的非线性特性研究

讨论了在静电场作用下，双势阱分子中波函数随外加静电场定域的动态过程，以及能级裂距与外加静电场的关系.证明了静电场作用后，能级裂距既受隧道效应的影响，又受外加静电场的影响.所加静电场较小时与外场强度呈非线性关系，当外加静电场较大时，Stark效应对能级裂距的影响占了主导地位，使能级裂距随外加静电场线性地增大. 关键词： 双势阱 静电场 隧道效应 能级裂距     

Optical bistability via tunable Fano-type interference in asymmetric semiconductor quantum wells

We analyze hybrid absorptive-dispersive optical bistability (OB) behavior via tunable Fano-type interference based on intersubband transitions in asymmetric double quantum wells (QWs) driven coherently by a probe laser field by means of a unidirectional ring cavity. We show that OB can be controlled efficiently by tuning the energy splitting of the two excited states (the coupling strength of the tunnelling), the Fano-type interference, and the frequency detuning. The influence of the electronic cooperation parameter on the OB behavior is also discussed. This investigation may be used for optimizing and controlling the optical switching process in the QW solid-state system, which is much more practical than that in atomic system because of its flexible design and the controllable interference strength.     

Frequency and intensity readouts of micro-wave electric field using Rydberg atoms with Doppler effects

A scheme of electric-field measurement of micro-waves is proposed in Rydberg atoms with Doppler effects. A cascade-type electromagnetically-induced-transparency (EIT) system is disturbed by a perturbative field coupling a metastable transition. The original dark state splits and two EIT window appear with a central absorption peak. When a micro-wave (MW) field couples the Rydberg transition, the central absorption peak is divided into two. The frequency splitting of two central peaks is proportional to the MW field intensity, which can be used to probe MW electric field strength. This frequency-readout method based on a double-dark state system increases the probe sensitivity nearly by a factor of 7, compared with that of the single-dark state case. At room temperature, Doppler effects can enhance the absorption spectrum, moreover, its peak value varies linearly with the MW field strength. This can also serve to measure MW electric field strength. Numerical results show that the latter intensity-readout method after Doppler averaging improves the probe sensitivity by a factor of 10 with respect to the case without Doppler effects.