The Decoherence of Single Electron Quantum Dot Qubit

On the condition of electric-LO phonon strong coupling in parabolic quantum dot, we obtain the eigenenergies of the ground state and the first-excited state, the eigenfunctions of the ground state and the first-excited state by using variational method of Pekar type. This system in quantum dot may be employed as a two-level quantum system-qubit. The phonon spontaneous emission causes the decoherence of the qubit. We displayed the density matrix of the qubit decayed with the time evolution and the coherence term of the density matrix element p ₁₀ (or p ₀₁) decayed with the time evolution for different coupling strength, the confinement length, the coefficient dispersion.     

Properties of an exact crystalline many-body ground state

A new quantum many-body Hamiltonian is introduced, for which the exact ground state is a Jastrow-type product. This Hamiltonian is interpreted as a one-component |x|-potential Coulomb system in free boundary conditions, and by explicit calculation it is shown that the ground state is crystalline. The generaln-body density matrix is calculated, and is related to then-body density matrix calculated in periodic boundary conditions.     

Non-Linear Transformations and Their Applications in Many-Body Physics

The transformations of the type which convert an exponential into a Gaussian and vice-versa and their applications in various areas of many-body physics are discussed. A new and general method of obtaining such transformations is given using the method of moments. It is compared with other methods which could be employed to obtain such transformations. In atomic physics, we have shown how such transformations can be used to obtain electron interaction energy for the ground state of Helium and Wigner transform for the ground state of H atom. It is shown how to bring angular momentum operators to linear form so that one can use the usual property of rotation operator to calculate their matrix elements. A new way of calculating the approximate eigenvalues of a Hamiltonian is given which combines the variational principles with the principle of maximum entropy. The anharmonic oscillator Hamiltonian is used to illustrate this new method. An interesting aspect of these transformations is that one could combine them with other transformations like Grassmann integration to calculate quantities of physical interest in closed form. A general matrix element of the harmonic oscillator is given which can be used to calculate usual quantities like the trace and density matrix. Some future applications are also discussed.     

Multichannel excitation cross sections of sodium atoms at slow collisions with hydrogen atoms

Excitation cross sections at slow collisions of hydrogen and sodium atoms are calculated based on two sets of quantum-chemical data. The results of calculations permit one to conclude that, upon the excitation of the sodium atom from the ground state in the region of near-threshold energies, the cross sections are highly sensitive to matrix nonadiabaticity elements. In addition, the matrix nonadiabaticity element was varied for the transition 3s → 3p of the sodium atom at fixed collision energy near the reaction threshold. It was found that the variation leads to a significant change in the excitation cross section 3s → 3p, and the range of the energetic dependence of this cross section was determined.     

On the ground state of the half-filled Hubbard model

We calculate the ground state of the half-filled Hubbard model and its energy by starting from a spindensity wave approximation and improving it by incorporating transverse spin fluctuations. The calculations are done by employing a projection method. The quality of the proposed approximation is particularly high for intermediate and large Coulomb repulsionU, where it exceeds considerably e.g. that of the Gutzwiller projected spin-density wave state. To ordert ²/U (wheret is the hopping matrix element), our approximation is shown to be equivalent to a recent Coupled Cluster calculation for the Heisenberg antiferromagnet. Finally we show how to ordert ²/U the linear spin-wave approximation for the Heisenberg antiferromagnet may be obtained.     

Matrix element of the anomalously low-energy (3.5±0.5 eV) transition in 229Th and the isomer lifetime

The matrix element of the anomalously low-energy (3.5±0.5 eV) nuclear M1 transition between the first excited state and the ground state of the ²²⁹Th nucleus is determined with allowance for the Coriolis mixing of the rotational bands. The upper and lower limits on the lifetime of the level with respect to an isomeric transition are given. A method is proposed for measuring the half-life of the low-lying isomer ^229m Th directly in a ²³³U sample. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 4, 233–238 (25 February 1998)     

The influence of the matrix element on angle-resolved photoemission spectra of insulating cuprates

Microscopic model calculations of the matrix element of a dipole moment are carried out in terms of the cluster model. This matrix element determines the transition probability of electron photoemission from a one-electron orbital with symmetry γμ to a free state. The effect of the matrix element on the angular and polarization dependences in the angle-resolved photoemission spectra of insulating cuprates, such as Sr₂CuO₂Cl₂ and Ca₂CuO₂Cl₂, is analyzed under the assumption of a well-isolated ground state of the two-hole CuO ₄ ^5? cluster, namely, the Zhang-Rice singlet. The angular k dependence of the matrix element gives rise to effects, such as the residual Fermi surface, which are typical of metallic systems. An analysis of the experimental data reveals the presence of another electronic state (with different symmetry) in the vicinity of the Zhang-Rice singlet.     

Correspondences of the vibrational frequencies of the ground and electronic excited states of quinoxaline as revealed by the Raman intensities

The intensities of the Raman lines of quinoxaline were measured at different excitation wavelengths. The matrix element ratios of the vibronic couplings between the two lowest electronic excited states of the molecule were evaluated from the Raman intensities of the b₁ vibrations, and they were compared with the matrix element ratios obtained from the vibrational frequencies of the ground and electronic excited states of the molecule. It was suggested that the ground state frequency of the b₁ vibration at 867 cm^?1 decreases greatly to 425 cm^?1 in the lowest $\text{nπ}{}^1$ excited state.     

Quantum spin-{3 \over 2} models on the Cayley tree - optimum ground state approach

We present a class of optimum ground states for quantum spin- models on the Cayley tree with coordination number 3. The interaction is restricted to nearest neighbours and contains 5 continuous parameters. For all values of these parameters the Hamiltonian has parity invariance, spin-flip invariance, and rotational symmetry in the xy-plane of spin space. The global ground states are constructed in terms of a 1-parametric vertex state model, which is a direct generalization of the well-known matrix product ground state approach. By using recursion relations and the transfer matrix technique we derive exact analytical expressions for local fluctuations and longitudinal and transversal two-point correlation functions. Received 1 March 1999     

Study of Some Factors Affecting Thermodynamic Properties of the Insulating Phase of the Periodic Anderson Lattice Model

Within the framework of slave-boson mean-field theory, we study the thermodynamic properties of the periodic Anderson lattice model with half-filled conduction band and one 4f electron at each primitive cell and the degeneracy N_d = 2. It is found that after taking into account the direct nearest-neighbor f-f hopping, such a periodic Anderson lattice model can exhibit both an insulating ground state and a heavy-fermion metal ground state depending on the value of the bare f energy level E_f, the hybridization matrix element V, and the direct f-f hopping strength δ. This is unlike the case neglecting the direct f-f hopping, in which such a periodic Anderson lattice model will predict an insulating ground state only.     

Luminescent characteristics of ZrO<Subscript>2</Subscript>:Pb nanopowders

ZrO₂ nanopowders doped with Pb ions are prepared by the coprecipitation method. The average size of the powders, measured by X-ray diffraction, is 4–6 nm. The emission spectra show a narrow band originating from the transition from the ¹S₀ ground state to the ³P₁ excited state of the Pb ions. A quenching of the photoluminescence is observed when the concentration of Pb²⁺ is higher than 5%. The influence of residual chlorine ions on the luminescent properties of the nanopowders is also discussed. PACS 78.55.-m; 81.05.Je; 61.72.Ww     

Entanglement and Density Matrix of a Block of Spins in AKLT Model

We study a 1-dimensional AKLT spin chain, consisting of spins S in the bulk and S/2 at both ends. The unique ground state of this AKLT model is described by the Valence-Bond-Solid (VBS) state. We investigate the density matrix of a contiguous block of bulk spins in this ground state. It is shown that the density matrix is a projector onto a subspace of dimension . This subspace is described by non-zero eigenvalues and corresponding eigenvectors of the density matrix. We prove that for large block the von Neumann entropy coincides with Renyi entropy and is equal to . NSF Grant DMS-0503712.     

Dooble beta decay: Operator expasion method revisited

The Operator Expansion Method (OEM) for the calculation of two-neutrino double beta decay (2ν2β-decay) is reconsidered. The assumed two-body Hamiltonian, in contrast to the ones considered previously, allows a consistent derivation of the OEM transition operators. The OEM is combined with the renormalized proton-neutron QRPA (pn-RQRPA) ground state wave functions and the 2ν2β-decay of⁷⁶Ge is calculated. The influence and relative importance of the central, tensor and Coulomb interactions are investigated. We have found that the strong suppression of the nuclear matrix elementM _GT has its origin in the choice of the pn-RQRPA ground state wave functions of the initial and final nuclei. Presented by M. Veselsky at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31, 1997.     

Spin Operator Matrix Elements in the Superintegrable Chiral Potts Quantum Chain

We derive spin operator matrix elements between general eigenstates of the superintegrable ℤ _N -symmetric chiral Potts quantum chain of finite length. Our starting point is the extended Onsager algebra recently proposed by Baxter. For each pair of spaces (Onsager sectors) of the irreducible representations of the Onsager algebra, we calculate the spin matrix elements between the eigenstates of the Hamiltonian of the quantum chain in factorized form, up to an overall scalar factor. This factor is known for the ground state Onsager sectors. For the matrix elements between the ground states of these sectors we perform the thermodynamic limit and obtain the formula for the order parameters. For the Ising quantum chain in a transverse field (N=2 case) the factorized form for the matrix elements coincides with the corresponding expressions obtained recently by the Separation of Variables method.     

Extended RPA with ground-state correlations

We propose a time-independent method for finding a correlated ground state of an extended time-dependent Hartree-Fock theory, known as the time-dependent density matrix theory (TDDM). The correlated ground state is used to formulate the small amplitude limit of TDDM (STDDM) which is a version of extended RPA theories with ground-state correlations. To demonstrate the feasibility of the method, we calculate the ground state of ²² O and study the first 2 ⁺ state and its two-phonon states using STDDM.Received: 7 November 2003, Published online: 10 August 2004PACS: 21.10.Re Collective levels - 21.60.Jz Hartree-Fock and random-phase approximations - 27.30. + t      

Shell model description of the 14C dating beta decay with Brown-Rho-scaled NN interactions

We present shell model calculations for the beta decay of 14C to the 14N ground state, treating the states of the A=14 multiplet as two 0p holes in an 16O core. We employ low-momentum nucleon-nucleon (NN) interactions derived from the realistic Bonn-B potential and find that the Gamow-Teller (GT) matrix element is too large to describe the known lifetime. By using a modified version of this potential that incorporates the effects of Brown-Rho scaling medium modifications, we find that the GT matrix element vanishes for a nuclear density around 85% that of nuclear matter. We find that the splitting between the (J(pi),T)=(1(+),0) and (J(pi),T)=(0(+),1) states in 14N is improved using the medium-modified Bonn-B potential and that the transition strengths from excited states of 14C to the 14N ground state are compatible with recent experiments.     

Continuously infinite commensurate-incommensurate phase transition of a two-dimensional competing Ising model

We consider the critical behavior of a two-dimensional competing axial Ising model including interactions up to third nearest neighbors in one direction. On the basis of a low-temperature analysis relating the transfer matrix of this model with the Hamiltonian of theS = 1/2XXZ chain, it is shown that the usual square root singularity dominating commensurate-incommensurate phase transitions of two-dimensional systems merges into a continuously infinite transition for certain relations among the coupling parameters. The conjectured equivalence between the maximum eigenstate of the transfer matrix associated with this model and the ground state of theXXZ chain is tested numerically for lattice widths up to 18 sites.     

The effect of oxygen on the sputtering of metastable atoms and ions from Ba metal

By means of the Doppler-Shift-Laser-Fluorescence technique we have measured the effect of oxygen coverage on the velocity distributions and relative yields of sputtered Ba atoms and ions in both the ground and metastable excited states. Our measurements show no evidence that the excitation probabilities are correlated with the magnitude of the electric-dipole-moment matrix element to the ground state. We also find that the excitation probability of the Ba(¹ D) state from a clean metal surface depends strongly on the emission velocity υ and approaches the functional form exp$\text{(}\text{?A}\text{av}\text{)}$ at higher velocities.     

使用时间切片离子速度成像技术研究CF2Cl2光解动力学

本文使用时间切片离子速度成像技术结合共振增强多光子电离技术研究了CF₂Cl₂分子在235 nm附近的光解动力学. 通过测量CF₂Cl₂分子在235 nm附近单光子解离产生的氯原子影像,直接得到了解离产物的速度分布和角分布. 激发态氯原子的速度分布包含高动能组分和低动能组分,分别对应³Q₀电子态的直接解离和由于内转换引起的基态预解离. 基态氯原子的速度分布也包含高动能组分和低动能组分,分别对应³Q₀与¹Q₁电子态的预解离和由于内转换引起的基态预解离. 自由基解离通道被确认,二次解离通道和三体解离通道被排除.     

Ground State and Spin-Glass Phase of the Large-N Infinite-Range Spin Glass via Supersymmetry

The large-N infinite-range spin glass is considered, in particular, the number of spin components k needed to form the ground state and the sample-to-sample fluctuations in the Lagrange multiplier field on each site. The physical significance of k for the correlation functions is discussed. The difference between the large-N and spherical spin glass is emphasized; a slight difference between the average Lagrange multiplier of the large-N and spherical spin glasses is derived, leading to a slight increase in the energy of the ground state compared to the naive expectation. Further, there is a change in the low-energy density of excitations in the large-N system. A form of level repulsion, similar to that found in random matrix theory, is found to exist in this system, surviving interactions. Even though the system is an interacting one, a supersymmetric formalism is developed to deal with the problem of averaging over disorder.