Spontaneous emission spectrum of a three-level atom embedded in photonic crystal

The two models of three-level (one upper level and two lower levels, or two upper levels and one lower level) atom embedded in a double-band photonic crystal are adopted. The atomic transitions from the upper levels to the lower levels are assumed to be coupled by the same reservoir which are respectively the isotropic photonic band gap (PBG) modes, the anisotropic PBG modes and the free vacuum modes. The effects of the fine structure of the atomic ground state levels in the model with one upper level and two lower levels, and the quantum interferences in the model with two upper levels and one lower level on the spontaneous emission spectrum of an atom are investigated in detail. Most interestingly, it is shown that new spontaneous emission lines are produced from the fine splitting of atomic ground state levels in the isotropic PBG case. The quantum interferences induce additional narrow spontaneous lines near the transition from the empty upper level to the lower level.     

Theoretical Analysis of the Exotic Structure of ^17F

The first excited state and the ground state of ^17F are studied with the asymptotic normalization coefficient method. The results show that the probabilities of the last proton being out of the binding-potential in both the states are P = 59.71% and P = 27.61%, respectively. This means that the last nucleon in both the states of ^17F is far-extended beyond the range of nuclear force, especially in the first excited state. This result is also verified by the calculation of the density distributions of the last proton in ^17F. It is quantitatively confirmed that the first excited state of^1TF is a nuclear halo state and its ground state is a proton skin state.     

Vibrational frequency of a strong-coupling polaron in a quantum rod at finite temperatures

The Hamiltonian of a quantum rod with a boundary is presented after a coordinate transformation that changes the original ellipsoidal boundary into a spherical one. We then study the effect of temperature on the vibrational frequency and the ground state binding energy of the strong-coupling polaron in the rod. The two quantities are expressed as functions of the aspect ratio of the ellipsoid, the transverse and the longitudinal effective confinement lengths, the temperature and the electron—phonon coupling strength by linear combination operator and unitary transformation methods. It is found that the vibrational frequency and the ground state binding energy will increase rapidly with decreasing transverse and longitudinal effective confinement lengths. They are increasing functions of the electron—phonon coupling strength but become decreasing ones of the temperature and the aspect ratio.     

Logarithmic Quantum Time Crystal

We investigate a time-independent many-boson system, whose ground states are quasi-degenerate and become infinitely degenerate in the thermodynamic limit. Out of these quasi-degenerate ground states we construct a quantum state that evolves in time with a period that is logarithmically proportional to the number of particles,that is, T ～ log N. This boson system in such a state is a quantum time crystal as it approaches the ground state in the thermodynamic limit. The logarithmic dependence of i...     

Entropy squeezing of the field interacting with a nearly degenerate V-type three-level atom

The position- and momentum-entopic squeezing properties of the optical field in the system of a nearly degenerate three-level atom interacting with a single-mode field are investigated. Calculation results indicate that when the field is initially in the vacuum state, it may lead to squeezing of the position entropy or the momentum entropy of the field if the atom is prepared properly. The effects of initial atomic state and the splitting of the excited levels of the atom on field entropies are discussed in this case. When the initial field is in a coherent state, we find that position-entropy squeezing of the field is present even if the atom is prepared in the ground state. By comparing the variance squeezing and entropy squeezing of the field we confirm that entropy is more sensitive than variance in measuring quantum fluctuations.     

Calculation of the elastic scattering properties for cold and ultracold 39K atoms in a triplet state

The elastic scattering properties for collisions between cold and ultracold 39K atoms in a triplet state are investigated. Based on the recent theoretical and experimental results, the improved hybrid potential is presented for a triplet α3∑u^＋ ground state of K2. Our calculated value of the s-wave scattering length a by using the Numerov method for the triplet state is 79.578α0 and found to be in good agreement with the previous ones. The numbers of bound states are supported by the molecular potential. Pronounced shape resonances appear for the l = 3 partial waves for the α3∑u^＋ state. Furthermore, the s-wave scattering cross section, the total cross section and energy positions of shape resonances for the α3∑u^＋ state are calculated.     

Frequency Dependence of Polarization Mode Dispersion in a Crystal-Based Polarization Mode Dispersion Compensator

We report the frequency dependence of polarization mode dispersion (PMD) in a PMD compensator based on six cascaded birefringent crystals separated by Faraday rotators. When all crystal axes are aligned, the device can compensate for the first-order PMD. However, if all crystal axes are coupled with arbitrary angles, it can compensate for high-order PMD. The variations of differential group delay and principal state of polarization with optical frequency are analysed. The PMD vector and Stokes components of the device versus wavelength are measured. The theoretical simulations agree well with the experimental results.     

Measurement of the argon-gas-induced broadening and line shifting of the barium Rydberg level 6s24d 1D2 by two-photon resonant nondegenerate four-wave mixing

We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state to the obser-vation of the broadening and shifting of the barium Rydberg level 6s24d 1^D2 by collision with argon. The collision broadening and shifting cross sections are measured. This technique is purely optical, and can investigate the pressure dependence of the transverse relaxation rate-P21 between the Rydberg state and an intermediate state, as well as the transverse relaxation rate F20 between the Rydberg state and the ground state.     

Measurement of the argon-gas-induced broadening and line shifting of the barium Rydberg level 6s24d ¹D₂ by two-photon resonant nondegenerate four-wave mixing

We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state to the observation of the broadening and shifting of the barium Rydberg level 6s24d 1D2 by collision with argon.The collision broadening and shifting cross sections are measured.This technique is purely optical,and can investigate the pressure dependence of the transverse relaxation rate Γ21 between the Rydberg state and an intermediate state,as well as the transverse relaxation rate Γ20 between the Rydberg state and the ground state.     

Effects of Magnetic Field on the Valence Bond Property of the Double—Quantum—Dot Molecule

The effects of the magnetic field on the valence bond property of the double-quantum-dot molecule are numerically studied by the finite element method and perturbation approach because of the absence of cylindrical symmetry in the horizontally coupled dots.The calculation results show that the energy value of the ground state changes differently from that of the first excited state with increasing magnetic field strength,and they cross under a certain magnetic field.The increasing magnetic field makes the covalent bond state change into an ionic bond state,which agrees qualitatively with experimental results and and makes ionic bond states remain.The oscillator strength of transition between covalent bond states decreases distinctly with the increasing magnetic field strength,when the molecule is irradiated by polarized light.Such a phenomenon is possibly useful for actual applications.     

Spontaneous transition of one-dimensional plasma photonic crystal’s orientation in a dielectric barrier discharge

A novel one-dimensional plasma photonic crystal whose crystal orientation can change spontaneously is demonstrated using a dielectric barrier discharge with two liquid electrodes. The orientation of the plasma photonic crystal will vary from transverse to longitudinal or vary from longitudinal to transverse and then revert to longitudinal by self-adjustment, while the experimental conditions are kept fixed. The dispersion relation of these plasma photonic crystals are calculated, and the changes of the photonic band diagrams during the orientation transition are studied.     

Relativistic R-matrix studies of photoionization processes of Ar^5＋

The 3s–np photoionization processes of the ground state 2P1/2 and the metastable state 2P3/2 of Ar5＋ are investigated using our recently developed relativistic R-matrix code, where the interactions between the bound states and the continuum states are included. Both resonance positions and the oscillator strengths are in much better agreement with the absolute experimental measurements by Wang et al.[Wang J C, Lu M, Esteves D, Habibi M, Alna’washi G and Phaneuf R A 2007 Phys. Rev. A 75 062712] with a resolution of 80 meV than their theoretical results. The contributions of the two experimental unresolved transitions are distinguished in our calculations, which show that the transitions from the ground state also make significant contributions to some resonances. Our theoretical results are also in good agreement with the measurements for the first resonance with a higher resolution of 20 meV.     

On the Ground State of Spin Systems with Orbital Degeneracy

In order to understand the properties of the spin system with orbital degeneracy,we first study the ground state of the SU(4) spin-orbital model on a square lattice.The mean-field results suggest that for a small Hund‘s interaction,the flavor liquid state is stable against the solid state,but with sufficient deviation from the SU(4) limit the long-range order may be attained in 2D system.Furthermore,we employ a variational approach to calculate the phase diagram of the ground state and the temperature-dependent susceptibility by taking into account the Hund‘s interaction and the anisotropy in orbital wavefunctions.Finally,the implications for the experimental observations on the material,LiNiO2,are discussed.     

Energy of a Polaron in a Wurtzite Nitride Finite Parabolic Quantum Well

The effects of electron-phonon interaction on energy levels of a polaron in a wurtzite nitride finite parabolic quantum well （PQW） are studied by using a modified Lee-Low-Pines variational method. The ground state, first excited state, and transition energy of the polaron in the GaN/Al0.3Ga0.7N wurtzite PQW are calculated by taking account of the influence of confined LO（TO）-like phonon modes and the half-spaee LO（TO）-like phonon modes and considering the anisotropy of all kinds of phonon modes. The numerical results are given and discussed. The results show that the electron-phonon interaction strongly affects the energy levels of the polaron, and the contributions from phonons to the energy of a polaron in a wurtzite nitride PQW are greater than that in an A1GaAs PQW. This indicates that ehe electron-phonon interaction in a wurtzite nitride PQW is not negligible.     

Structures of ^17F and ^17O, ^17Ne and ^17N in the Ground State and the First Excited State

The structures of two couples of mirror nuclei ^17F and ^17O, ^17Ne and ^17N in the ground state and in the first excited state are investigated using the relativistic mean-field approach. Two-proton halo in ^17Ne in the first excited state and in the ground state and two-neutron halo in ^17N in the first excited state are suggested.Meanwhile, one-proton halo in ^17F in the first excited state and one-neutron halo in ^17O in the first excited state are also suggested. The skin structure appears in ^17F and ^17N in the ground state.     

Properties of the β-Delayed Proton Decay of 147Er

The β-delayed proton decay of 147Er is studied experimentally using the 58 Ni＋92Mo reaction at a beam energy of 383 MeV. Based on a He-jet apparatus coupled with a tape transport system, the β-delayed proton radioactivities both from the vδl/2 ground state and the vh11/2 isomer in 147 Er are identified by proton-7 coincidence measurements. By analyzing the time distribution of the 4＋ → 2＋-γ transition in the grand-daughter nucleus 146Dy, a half-life of 1.6 ± 0.2s is determined for the Vh11/2 isomer in 147 Er. The half-life for the ground state of 147Er is estimated to be 3.2±1.2 s.     

Squeezing Effect of a Nanomechanical Resonator Coupled to a Two-Level System: an Equilibrium Approach

The squeezing effect of a nanomechanical resonator coupled to a two-level system is studied by variational calculations based on both the displaced-squeezed-state （DSS） and the displaced-oscillator-state （DOS）. The stable region of the DSS ground state at both T = 0 and T ≠ 0 and the corresponding squeezing factor are calculated. It is found that when the resonator frequency lies in （kBT,△）, where A is the tunnelling splitting of the two-level-system in the presence of dissipation, tunnelling splitting of a DSS ground state decreases with the temperature, while tunnelling splittihg of a DOS ground state increases with the temperature in low temperature region. This opposite temperature dependence can help to distinguish between the DSS and DOS ground state in the experiment.     

The Mixed Spin-1/2 and Spin-1 Ising–Heisenberg Model in the Mean-Field Approximation: a New Approach

Thermodynamic properties of the mixed spin-1 and spin-1/2 Ising–Heisenberg model are studied on a honeycomb lattice using a new approach in the mean-field approximation to analyze the effects of longitudinal D_z and transverse D_x crystal fields. The phase diagrams are calculated in detail by studying the thermal variations of the order parameters, i.e., magnetizations and quadrupole moments, and compared with the literature to assess the reliability of the new approach. It is found that the model yields both second-and first-order phase transitions, and tricritical points. The compensation behavior of the model is also investigated for the sublattice magnetizations, and longitudinal and transverse quadrupolar moments. The latter type of compensation is observed in the literature but its possible importance is overlooked.     

Ionization of Atoms and the Thomas－Fermi Model for the Electric Field in Crystal Planar Channels

The electric field in the crystal planar channels is studied by the Thomas-Fermi method.The ThomasFermi equation and the corresponding boundary conditions are derived for the crystal palanar channels,The numerical solution for the elctric field in the channels between(110) Planes of the single crystal silicaon and the critical angles of channelling protons in them are shown.Reasonable agreements with the experimental data are obtained.The results show that the Thomas-Fermi method for the crystal works well in this study,and a microscopic research of the channel electric field with the contribution of all atoms and the atomic ionization being taken into account is practical.     

The study of magnetization of the spin system in the ground state

Within the framework of the effective-field theory with self-spin correlations and the differential operator technique, the ground state magnetizations of the biaxial crystal field spin system on the honeycomb lattices have been studied. The influences of the biaxial crystal field on the magnetization in the ground state have been investigated in detail.