Vol 39, No 1 (2018)

We present a detail study of the evolution of nonlocal correlations of an interacting quantum system comprising a three-level atom and a field mode initially prepared in a squeezed vacuum state with added photons. We compare the dynamical behavior of the quantum phase and entanglement by varying the number of photons added to the squeezed vacuum state. Furthermore, we examine the influence of the added-photon number and the squeeze parameter on the dynamical behavior of entanglement, quantum phase, and nonclassical properties of the field. Moreover, we explore the link between the quantum phase and the nonlocal correlation. Finally, we introduce an effective method to generate and maintain a high level of entanglement for this quantum system based on precise parameter ranges.

We present a two-level atomic Bose–Einstein condensate (BEC) with dispersion, which is coupled to a high-finesse optical cavity. We call this model the extended Jaynes–Cummings–Dicke (JC-Dicke) model and introduce an effective Hamiltonian for this system. From the direct product of Heisenberg–Weyl (HW) coherent states for the field and U(2) coherent states for the matter, we obtain the potential energy surface of the system. Within the framework of the mean-field approach, we evaluate the variational energy as the expectation value of the Hamiltonian for the considered state. We investigate numerically the quantum phase transition and the Berry phase for this system. We find the influence of the atom–atom interactions on the quantum phase transition point and obtain a new phase transition occurring when the microwave amplitude changes. Furthermore, we observe that the coherent atoms not only shift the phase transition point but also affect the macroscopic excitations in the superradiant phase.

We propose and investigate an effective method for obtaining high-energy and high-intensity isolated attosecond pulses (IAPs) using the inhomogeneous double optical gating (DOG) technology in specifically designed metal nanostructures. First, using the homogeneous mid-infrared DOG technology modulated by a linearly near-infrared field, we obtain a harmonic yield of 2.5 orders of magnitudes higher than that from the single polarization gating (PG) technology. Further, introducing the crossed metal nanostructures along the driven and gating components, we can extend not only the harmonic cutoff but also enhance the harmonic yield attributed to the plasmonic field enhancement near the vicinity of metal nanostructures. As a result, we find a single harmonic plateau with smaller modulations. The supercontinuum is not very sensitive to the pulse duration of the near-infrared field, and the harmonic yields can be further enhanced with increase in the pulse intensity of the near-infrared field, showing a 108 eV supercontinuum with an intensity enhancement of 4 orders of magnitudes. Finally, by superposing the selected harmonics from the inhomogeneous DOG scheme, we obtain a 33 as SAP with an intensity increase of 4 orders of magnitudes.

We study the room-temperature (RT) pulsed cathodoluminescence (PCL) spectra of a set of pure synthetic (both crystalline and amorphous) silicon dioxide samples. We show that the PCL spectra of all samples (both amorphous and crystalline) possess bands with intensity maxima in the region of 487 – 500 nm (2.54 – 2.48 eV). These bands are the most intense in the PCL spectra of disordered materials. We investigate the annealing behavior of RT PCL spectra of the crystalline and amorphous samples. Annealing has no significant effect on this emission. We demonstrate that the surface area of the material plays no role in the emission of PCL bands at 415 and 490 nm in the spectra of α-quartz single crystal and crystalline powder with grain sizes of 10 – 100 μm. Our results show that the bands in the region of 2.5 eV are the universal property of all synthetic pure SiO₂ samples. The nature of the SiO₂ emission band in the region of 2.5 eV is not clear; we discuss two possible explanations. The first one is based on considering the intrinsic emission due to self-trapped exciton (STE) decay with the transient O-O (oxygen–oxygen) bond formation. The second one is based on the role of Li ions in the emission process.

We realize for the first time an experimental investigation of the IR and visible luminescence of SiGe/Si heterostructures with quantum well subjected to an external anisotropic deformation. We show that tensile strain along the [100] direction enhances the absolute and relative intensities of visible luminescence by a factor of 7/3 at a temperature of 5 K. This effect is absent for a tensile strain along the [110] direction. We explain the phenomenon observed in view of the model of single-photon biexciton recombination for the system in which the bottom of the conduction band is formed by only two opposite electronic valleys.

We demonstrate a trace gas sensor to measure the water vapor (H₂O) concentration based on quartzenhanced photoacoustic spectroscopy (QEPAS). Here, the wavelength-modulation spectroscopy (WMS) with the second-harmonic detection is utilized. We add two metallic tubes acting as a microresonator (mR) to the quartz tuning fork (QTF) sensor design to improve the sensor signal level. After optimization of the mR dimensions and laser modulation depth, we obtain a minimum detection limit (MDL) of 5.73 ppm.