-type atomic system driven resonantly by three coherent fields in a closed-loop coupling configuration. Owing to phase-controlled quantum interference, the real part of the induced complex permittivity becomes negative with vanishing imaginary part over a finite range of probe detuning. As a consequence, the complex refractive index exhibits a vanishing real part at a specific spectral detuning. Under this condition, the reflectance of the probe beam entering the medium reaches unity with ultimate suppression of transmittance. This leads to the phenomenon of perfect optically induced reflection (OIR). The tunable nature of OIR provides a new route for manipulating light propagation. The present study holds promise for its applications in the field of photonics. To this aim, we have demonstrated a two-port all-optical switching application at low light levels.
-type atomic system driven resonantly by three coherent fields in a closed-loop coupling configuration. Owing to phase-controlled quantum interference, the real part of the induced complex permittivity becomes negative with vanishing imaginary part over a finite range of probe detuning. As a consequence, the complex refractive index exhibits a vanishing real part at a specific spectral detuning. Under this condition, the reflectance of the probe beam entering the medium reaches unity with ultimate suppression of transmittance. This leads to the phenomenon of perfect optically induced reflection (OIR). The tunable nature of OIR provides a new route for manipulating light propagation. The present study holds promise for its applications in the field of photonics. To this aim, we have demonstrated a two-port all-optical switching application at low light levels.
In recent years, it has been a hot research topic to study the interaction between atomic ensemble and cavities, and many researches have been done in this regard. In such a system, some atoms are trapped in the cavity, which can be used to study their dynamic characteristics, e.g., the evolution of photon numbers and photon transition. The Jaynes-Cummings model is an important model for studying the dynamic characteristics of the cavity-atom system, which is based on the interaction between a single two-level atom and the cavity field. Recently, coherent photon control in cavity under specific conditions has become an important part of quantum computing and communication. It is worth noting that the tunable photon transmission and all-optical switches based on the cavity have already aroused much interest and have been used in many areas. The quantum information and networks are mostly rooted in complex optical devices, which may show nonreciprocal or asymmetric photon transport. In this paper, we demonstrate that by using an optical closed-loop system the unconventional photon transport can be realized with two mutually perpendicular cavities coupled through external fiber and a two-level atom placed on the intersection. This three-mode system supports two orthogonal propagation directions, that is to say, and the interactions among probe fields are mutually perpendicular. Without ignoring the spontaneous decay of the natural atom, the complex and controllable quantum interference induced by the efficient hybrid interaction of the light, cavity modes, and the atom in such a closed-loop structure can result in a few interesting symmetric and asymmetric photon transport behaviors, i.e. coherent perfect synthesis and coherent perfect reflection. Aside from these compelling properties, the group velocity can also be modulated, i.e., fast and slow light effect. All of these processes can be dynamically controlled by using the probe field phase difference, the tunneling coupling between two cavities and the coupling between the cavity and the atom. Importantly, due to so many advantages, such a tunable scheme can be readily extended to some optical devices, e.g., the switch and the router that is challenging to conventional optical devices.
We propose a scheme for controlling coherent photon absorption by electromagnetically induced transparency (EIT) in a three-level atom-cavity system. Coherent perfect absorption (CPA) occurs when time-reversed symmetry of lasing process is obtained with the destructive interference at the cavity interfaces. The frequency range of CPA is generally dependent on the decay rates of the cavity mirrors. The smaller decay rate of the cavity mirror causes the wider frequency range of CPA, and the needed intensity of the probe fields is larger to satisfy CPA condition for a given frequency. Although Rabi frequency of the control laser has little effect on the frequency range of CPA, with EIT-type quantum interference, the CPA mode is tunable by the control laser. In addition, with the relative phase, the probe fields can be perfectly transmitted and/or reflected. Therefore, the system can be used as a controllable coherent perfect absorber or transmitter (reflector), and our work may have practical applications in optical logic devices.
The resonant absorption, emission, and scattering of light are the fundamental optical processes that have been used both to probe matter and to manipulate light itself. In the last decade there has been essential progress in coherent control of both linear and nonlinear optical responses based on resonant excitation of atomic coherence in multilevel quantum systems. Some interesting and useful phenomena, resulting from coherent control of absorption and the group index, such as electromagnetically induced transparency, lasing without inversion, and ultra-slow group velocity of light have been widely studied. This work is focused on coherent control of refractive index and resonant fluorescence in multilevel medium. \n \nWe suggest two promising schemes for resonant enhancement of the refractive index with eliminated absorption and propose their implementation in transition element doped crystals with excited state absorption and in a cell of Rb atoms at natural abundance. We show how to use one of these schemes for spatial variation of the refractive index via its periodic resonant increase/decrease, remarkably keeping at the same time zero absorption/gain. It opens the way to production of transparent photonic structures (such as distributed Bragg reflectors, holey fibers, or photonic crystals) in a homogeneous resonant atomic media such as dielectrics with homogeneously distributed impurities, atomic, or molecular gases. These optically produced photonic structures could easily be controlled (including switching on/off, changing amplitude and period of modulation) and would be highly selective in frequency, naturally limited by the width of the optical resonance. \n \nWe also derive the optical fluorescence spectra of a three-level medium driven by two coherent fields at the adjacent transitions in a general case when all three transitions are allowed. We show that coherent driving can efficiently control the distribution of intensities between the fluorescent channels. In particular, the total intensity of fluorescence at the transition which is not driven by the optical fields may essentially exceed the fluorescence intensity at the driven transitions under the condition of two-photon resonance. This counter-intuitive effect is due to depletion of the intermediate state via atomic interference.
This research focuses on a coherently driven four-level atomic medium with the aim of inducing a negative index of refraction while taking into consideration local field corrections as well as magnetoelectric cross coupling (i.e.,chirality) within the material's response functions. Two control fields are used to render the medium transparent for a probe field which simultaneously couples to an electric and a magnetic dipole transition, thus allowing one to test the permittivity and permeability of the material at the same time. Numerical simulations show that a negative index of refraction with low absorption can be obtained for a range of probe detunings while depending on number density and the ratio between the intensities of the control fields.
We propose a scheme in which an arbitrary incidence can be made perfectly reflected/transmitted if a phase setup is adjusted under a specific condition. We analyze the intracavity field variation as well as the output field with changing closed-loop phase of atomic system and relative phase of input probe beams. And we obtain the condition for perfect transmitter or reflector. By adjusting two phase setups, the medium absorption and light interference can be controlled so that photon escape from cavity can be modulated, thus the intensity switching based on phase control can be realized. Then based on the transmission/reflection analysis, total absorption of this system can be investigated. Therefore our scheme can be used as an absorption interferometer to explore the optical absorption in some complicated system. The phase delay dependent on phi_1 or phi_2 in output light intensity can be applied in the realization of quantum phase gate and subtle wave filter. And based on this scheme, we implement the state transfer between perfect transmitter/reflector and non-perfect coherent photon absorber via relative-phase modulation.
We theoretically study the optically tunable gratings based on a L-type atomic medium using coherent population oscillations from the angle of reflection and transmission of the probe field. Adopting a standing-wave driving field, the refractive index of the medium as well as the absorption are periodically modified. Consequently, the Bragg scattering causes the effective reflection. We show that different intensities of the control field lead to three types of reflection profile which actually correspond to different absorption/amplification features of the medium. We present a detailed analyses about the influence of amplification on the reflection profile as well. The coherent population oscillation is robust to the dephasing effect, and such induced gratings could have promising applications in nonlinear optics and all-optical information processing.