We consider a two-photon correlated emission laser as a source of an entangled radiation with a large number of photons in each mode. The system consists of three-level atomic schemes inside a doubly resonant cavity. We study the dynamics of this system in the presence of cavity losses, concluding that the creation of entangled states with photon numbers up to tens of thousands seems achievable.

An ultrathin and broadband absorber is investigated in this paper. The metamaterial absorber is composed of a periodic array of loop-dielectric multilayered structure. By tuning the scale factor of the loop and the height of every layer, a desirable refractive index dispersion spectrum is realized, which is the reason to realize a successive anti-reflection in a wide frequency range. The interference mechanism and resonance absorption are identified through analytical derivation and numerical simulations. Numerical results show that the absorption at normal incidence is above 90% in the frequency range of 8.37–21 GHz. Moreover, the structure has a thickness of 3.65 mm (only 0.10λ to 0.26λ at the lowest and highest frequencies, respectively). The explanation to the physical mechanism of the metamaterial absorber is presented and verified.

We discuss the generation of a macroscopic entangled state in a single atom cavity-QED system. The three-level atom in a cascade configuration interacts dispersively with two classical coherent fields inside a doubly resonant cavity. We show that a macroscopic entangled state between these two cavity modes can be generated under large detuning conditions. The entanglement persists even under the presence of cavity losses.

We report an experimental investigation of electromagnetically induced transparency in a multilevel cascade system of cold atoms. The absorption spectral profiles of the probe light in the multi-level cascade system were observed in cold 85 Rb atoms confined in a magneto-optical trap, and the dependence of the spectral profile on the intensity of the coupling laser was investigated.The experimental measurements agree with the theoretical calculations based on the density matrix equations of the rubidium cascade system.Electromagnetically induced transparency (EIT)[1] is a quantum interference effect that permits propagation of light through an opaque atomic medium without attenuation, it was first proposed in 1989 [2] and experimentally verified in 1991 [3]. Since then, theoretical and experimental studies of EIT have attracted great attentions due to their potential applications in many fields, such as low light nonlinear optics [4], quantum information [5], atomic frequency standard [6], and so on. Early studies were carried out with hot atoms in vapor cells. In the hot atomic medium, the interaction time between the atoms and the laser fields is short which leads to the transient broadening. Also, the collisions in the hot atomic medium may severely shorten the coherence decay time. Recently, many groups explored the EIT phenomena using the laser cooled atoms. There are several advantages in the cold atoms [7]. Firstly, because of the low temperature of the cold atoms, the Doppler broadening effect is effectively minimized, which renders it possible to explore EIT-type nonlinear optical phenomena involving odd number of photons. Secondly, the lower collision rates in the cold atomic sample reduce the decoherence rate.Early experimental studies of EIT in the cold atoms were mainly carried out in rubidium atoms [8,9,10]. Subsequently, the EIT based nonlinear optical phenomena were studied [4,11], which led to the recent experiments on the resonant nonlinear optics at low light intensity. A very steep slope of refractive index and the extremely low group velocity of probe light have been obtained in the cold EIT mediums [12], which have been used to demonstrate light storage and recall based on the coherent excitation transfer between the photons and the atoms [13]. Recently, electromagnetically induced grating (EIG) [14,15] was realized in the cold atoms. Jason et al. experimentally compared the EIT phenomena between the hot atoms and the cold atoms [16], and Ahufinger et al. compared the EIT phenomena between the cold atoms above and below the transition temperature for Bose-Einstein condensation [17]. These studies on EIT and the related phenomena in the cold atoms provided intensive understanding of the atomic coherence and interference in the fundamental interaction between the light field and the atoms [18,19,20,21,22,23].EIT in the simple three-level system have been extensively studied, but EIT in the multilevel cascade systems and their possible applications have not been fully explored. Although essenti...