In this paper, we have investigated three external fields interacting with the four-level atomic system described by the density-matrix approach. The atomic system exhibits left-handedness with zero absorption and large negative refractive index. Varying the parameters of the three external fields, the properties of zero absorption and large negative refractive index from the atomic system remain unvarying. Our scheme proposes an approach to obtain a negative refractive medium with zero absorption. The zero absorption property of the atomic system may be used to amplify the evanescent waves that have been lost in the imaging by traditional lenses, and a slab fabricated by the left-handed atomic system may be an ideal candidate for designing perfect lenses.

The paper demonstrates that negative refractive index can be achieved via tuning the tunneling rate between a double quantum dots (QDs) system by applying a bias voltage, and a pulsed laser. As the bias voltage being changed, the refraction index can be tunable to negative with the simultaneous negative permittivity and permeability. While the varying pulsed laser is applied to the double QDs system, moreover, the negative refractive index with little loss can be obtained. The flexible manipulation on a solid state system to realize negative refraction may give a new way for experimental research in the future.

Negative refractive index (NRI) of the quantized lossless mesoscopic left-handed transmission line (LHTL) is deduced numerically in thermal Fock state. Some specific quantum features of NRI dependent the temperature, frequency of the electromagnetic wave and photon numbers, and quantum fluctuations are shown in the lossless LHTL. The results are significant for the miniaturizing applications of LHTL and quantum circuits. Keywords Negative refractive index · Mesoscopic Left-handed transmission lines · Thermal Fock state 1 Introduction The theoretical speculation of negative refractive index materials (NRM) proposed by V. Veselago[1] in 1968, in which several fundamental phenomena occurring in or in association with NRM were predicted, such as the negative Goos-Hänchen shift[2], amplification of evanescent waves[3], reversals of both Doppler shift and Cerenkov radiation[1], sub-wavelength focusing[4] and so on. Some typical approaches for NRM can be summarized as artificial structures such as metamaterials[5-7] and photonic crystals[8-10], chiral materials[11] and photonic resonant media[12, 13]. Although very exciting from a physics point of view, the artificial structures seem to be of little practical interest for engineering applications because

Keywords: quantum dot photocell modeled by a multi-level system, photo-to-charge efficiency, low-energy photons, quantum yields AbstractTo absorb the photons below the band-gap energy effectively, we proposed a quantum dot (QD) photocell modeled by multi-level system for the quantum yields and photo-to-charge efficiency limits. The theoretical results show the quantum yields are enhanced as compared to the single band-gap solar cell, and the photo-to-charge efficiencies are larger than Shockley and Queisser efficiency in the same absorbed spectrum. What is more, at the room temperature the efficiency limits are well beyond 63% achieved by Luque and Marti (1997 Phys. Rev. Lett. 78 5014) due to absorbing the low-energy photons via two sub-bands in this proposed photocell system. The achievements may reveal a novel theoretical approach to enhance the QD photocell performance modeled a multi-level absorbing photons system.

No abstract