Entanglement witnesses for d ⊗ d systems and new classes of entangled qudit states

We provide a new class of entanglement witnesses for d ⊗ d systems (two qudits). Our construction generalizes the one proposed recently by Jafarizadeh et al. for d = 3 and d = 4 on the basis of semidefinite linear programming. Moreover, we provide a new class of PPT entangled states detected by our witnesses which generalizes well known family of states constructed by Horodecki et al. for d = 3.     

Linear optical implementation of a quantum network for quantum estimation

We present an interferometer for simulating the quantum network for quantum estimation proposed by A.K. Ekert et al. [A.K. Ekert, C.M. Alves, D.K.L. Oi, M. Horodecki, P. Horodecki, L.C. Kwek, Phys. Rev. Lett. 88 (2002) 217901]. We experimentally perform overlap measurements of two single-qubit states with linear optical elements. The scheme is generalized to perform estimation of Trρ³.     

Optical and ESR analysis of the Fe acceptor in InP

Photoluminescence (PL), optical absorption, and electron spin resonance (ESR) have been applied to detect the different charge states of substitutional Fe in InP. The 3d⁶ one electron trap state is detected by the PL and optical absorption lines of the ⁵T₂?⁵E transitions, whereas the 3d⁵ neutral acceptor state is identified by its characteristics S = 5/2 ESR signal.     

The Local Orthogonality Between Quantum States and Entanglement Decomposition

In the paper, we show that when a quantum state can be decomposed as a convex combination of locally orthogonal mixed states, its entanglement can be decomposed into the entanglement of these mixed states without losing them. The obtained result generalizes a corresponding one proved by Horodecki (Acta Phys. Slov. 48, 141 1998). But, for the entanglement cost it requires certain conditions for holding the decomposition, and the distillable entanglement only has a week result as inequality. Finally, we presented an example to show that the conditions of our conclusions are existence.     

Impurity Auger spectra: A probe of the local impurity density of state and the impurity electron—electron interactions

We show that the local impurity density of states and the impurity electron—electron interactions can be obtained from impurity Auger spectra. For a Ag_0.95Pd_0.05 alloy we find 11% Pd(d) character in the Ag d band and Pd(4d-4d) Coulomb interactions which are much larger than the virtual bound state widths.     

Revised model for 5d electrons in the heavy rare earth metals

A revised version of a recently published model for 5d electrons in the ferromagnetic state of the heavy rare earth metals is described. The model involves the broadening of local 5d states into overlapping bands with individual widthsW. In the new approach it is assumed that the local 5d wave functions lie at some point between those for atomic 4f _n 5d 6s ² configurations and those calculated for such configurations subject to the restriction that the 4f shell is kept with its moment rigidly fixed in some given direction. The admixture of non-aligned 4f states as in the atom lowers the local energy, but it also lowers the 5d bandwidth due to misfit of the 4f states which occur with and without the presence of a 5d electron. This second effect raises the energy of the low lying states in the band. The best local states are determined by minimising the total electronic energy of the system, using approximations which are most suitable for 4f shells with large excitation energies. Bandwidths are found by fitting the observed saturation magnetic moments in Gd and Tm, and satisfyW?1 eV.     

Many-body calculations of the hyperfine interaction of some excited states of alkali atoms,using approximate Brueckner or natural orbitals

The theory of maximum-overlap or Brueckner orbitals and of natural Orbitals is reviewed for closed-shell systems. A technique is described to calculate approximate Brueckner or natural orbitals for systems with a single valence electron, and this is applied together with the linked-diagram expansion of effective operators to evaluate the hyperfine interaction of some excited states of alkali atoms. It is found that it is in this way possible to reproduce reasonably well also the highly perturbed interactions of the excitedd states, which is not possible in a low-order expansion based on HF orbitals. Numerical results are given for the 5d state in K and the 4d state in Rb, where good experimental information is available.     

Surface resonant states and the adsorption of 4d atoms on Mo (110) and (100)

The adsorptive properties of Mo (110) and Mo (100) relative to 4d transition adatoms are investigated and compared using a tight-binding model. The surface resonant states existing on the (100) free surface are shown to have a drastic influence. On Mo (110) a Mo adatom retains a strong atomic character while on Mo (100) one approaches a surface molecule limit which is due to a strong interaction between the adsorbate atomic state and the free surface resonance. Consequently a large anisotropy of binding energy is found. The case of different 4d adatoms is also discussed.     

Quantum Tomography under Prior Information

We provide a detailed analysis of the question: how many measurement settings or outcomes are needed in order to identify an unknown quantum state which is constrained by prior information? We show that if the prior information restricts the possible states to a set of lower dimensionality, then topological obstructions can increase the required number of outcomes by a factor of two over the number of real parameters needed to characterize the set of all states. Conversely, we show that almost every measurement becomes informationally complete with respect to the constrained set if the number of outcomes exceeds twice the Minkowski dimension of the set. We apply the obtained results to determine the minimal number of outcomes of measurements which are informationally complete with respect to states with rank constraints. In particular, we show that the minimal number of measurement outcomes (POVM elements) necessary to identify all pure states in a d-dimensional Hilbert space is 4d?3?c(d) α(d) for some ${c(d)\in[1,2]}$ and α(d) being the number of ones appearing in the binary expansion of (d?1).     

Room temperature ferromagnetism in Cu–Gd co-doped GaN nanowires: A first-principles study

The electronic structure and room temperature ferromagnetism of wurtzite Cu–Gd co-doped GaN nanowires have been investigated by means of the first-principles calculations within the density functional theory, including the on-site Coulomb energy U. The magnetic coupling between Gd atoms in the Gd-doped GaN nanowire is paramagnetic instead of ferromagnetic (FM) as in the bulk structure. After replacing Ga with Cu atom we find a stable FM coupling between Gd magnetic moments in this p-type system. p–d coupling between Cu-3d and N-2p states pushes N-2p states up to Fermi level due to the existence of hole states introduced by Cu dopants. While the p–d coupling between host N-2p and Gd-5d states near Fermi level stabilizes a FM phase of Gd magnetic moments. Furthermore, we get a FM state above room temperature by increasing the holes concentration.     

Theoretical study of the spectroscopy of niobium nitride

State-averaged (SA) complete-active-space self-consistent-field (CASSCF) multireference configuration-interaction (MRCI) calculations are reported for the singlet and triplet states of NbN below about 20 000 cm⁻¹ and the quintet states below about 30 000 cm⁻¹. The theoretical spectroscopic constants for the four lowest triplet states, X³Δ, A³Σ⁻, B³Φ, and C³Π, are in excellent agreement with experiment. The calculations predict the ordering of states in the singlet manifold to be a¹Δ, b¹Σ⁺, c¹Γ, d¹Σ⁺, and e¹Π. These states have all been experimentally observed, except for the d¹Σ⁺ state near 13 000 cm⁻¹. The lowest quintet state, ⁵Π, is predicted to lie above 17 000 cm⁻¹. The calculations confirm the experimental conjecture, based on hyperfine splittings, that the X³Δ state is of predominantly 4dδ¹5s¹ character. Although the NbN molecule is very ionic, the ground-state dipole moment of 3.68 D is only moderately large, because of the polarization of the 5s electron away from nitrogen atom. Electronic transition moments are computed for all of the dipole-allowed transitions in the singlet and triplet manifolds. The radiative lifetimes for the v′ = 0 level are computed to be 37 ns, 35 ns, 1 μs, and 64 ns for the B³Φ, C³Π, d¹Σ⁺, and e¹Π states, respectively. For small v′, the largest Einstein coefficients all involve transitions with v′ = v″, because the transitions in NbN are nearly vertical. We constrast our results for NbN with similar calculations for the isoelectronic ZrO molecule. The considerable differences between the spectroscopy of ZrO and that of NbN are a result of the greater stability of the d orbitals for Nb, and the fact that Nb has a 4dⁿ⁺¹5s¹ ground state, whereas Zr has a 4dⁿ5s² ground state.     

Surface states ond-band metals

Electron surface states ond-band metals are investigated by the method of matching the crystal wave function to the outside solution at the surface. On a (100) surface of anfcc structure such a state is found near to the crossover of thes-band and thed-band of the same symmetry. In Ni this state lies 4–5 eV below the Fermi energy, for Cu 5–6 V beloweE _F. It explains the density of states anomaly seen in photoemission.     

Electroreflectance of bound excitonic states in semiconductors

While first-derivative spectroscopy (thermoreflectance, piezoreflectance, wavelength derivative modulation) has a general validity, no matter whether one is studying interband or excitonic transitions (involving also bound states), things are more complex in the case of electroreflectance (ER). As a matter of fact, Aspnes and Rowe's third-derivative theory does not include bound excitonic states. Using a phenomenological approach one can see that only in the case of a strong mixing between d³ε_r/dE³ and d³ε₁/dE³ it is possible to observe a qualitative agreement between Δε and d³ε/dE³ in some particular cases where Wannier excitonic series gives a predominant contribution to the optical spectra.     

Excited-state absorption spectroscopy from the 3d9 4s relaxed excited state of Cu+ in KBr and NaBr

Data on the low temperature optical absorption from the optically-pumped relaxed excited state 3d⁹ 4s of Cu⁺, substitutional in KBr, are here reported for the first time. These results are discussed and it is suggested that the absorption peaks at higher energies are due to transitions from the 3d⁹ 4s to states of the conduction band continuum.     

Empty electronic states in solid and liquid nickel

The density of empty electronic states in solid and liquid nickel has been determined employing Auger electron appearance potential spectroscopy. The observed increase of the density-of-states at the Fermi level by a factor of 1.4 in the liquid is in good agreement with available resistivity data. An increase of d-holes from 0.6 to 1.0 upon fusion is also found and interpreted in terms of a reduced d-d-interaction in the liquid state.     

On the volume dependence of the total energy and the equation of state for copper

The total energy of metallic copper as a function of the atomic radius is calculated. The model assumes that in copper one has nearly free s-electrons in OPW states and d-electrons localized at the ions in atomic-like orbitals. The coulomb interactions in the energy are calculated by using the model of neutral spheres, while the kinetic and exchange contributions to the S²-energy are approximated by the exchange charge model. Instead of the familiar Born-Mayer repulsion, which was found to lead to controversies in the case of copper, the d-type interaction energy shows a more complex behaviour having a minimum near the equilibrium atomic radius. The prediction for the cohesive energy and the equation of state is reasonable, the calculated value for the Ashcroft radius for s-electrons agrees remarkably with the ab initio estimate. The atomic-like orbitals minimizing the total energy are somewhat more extended than the real atomic wave-functions.     

Observation of the ABC effect and final-state isospin

Despite the number of inclusive measurements of the pionic fusion reactions, the nature of the ABC effect discovered in 1960 was not completely established. Exclusive measurements of the doublepion-production reactions leading to either fused d, ³He and ⁴He nuclear final states or pp pairs are analyzed. A significant ABC effect—enhancement in the region of low ππ mass—is found only in the isoscalar ππ channel while in the isovector channels it is small or absent. For the reaction with isovector pp final state an ABC effect was not observed even at the special kinematic conditions to reproduce a quasi-bound two-proton state. The total cross sections for the d and 4He fusion reactions show similar resonance-like energy dependence.     

Spin interactions in a quantum ring containing a magnetic impurity

The exciton states in a CdTe semiconductor quantum ring containing a single magnetic impurity are considered in an external magnetic field. The electron-hole spin interaction and s,p-d interactions between electron, hole and magnetic impurity are also taken into account in the calculations. It is shown that due to the s,p-d spin interactions the ground state exciton energy splits into 12 doubly degenerated energy levels. The external magnetic field removes this degeneracy. A novel method is proposed here to determine the values of the strengths of s,p-d interactions. The optical spectrum of the system for different polarizations of the incident light and for different initial states of the magnetic impurity spin projection is also studied.     

Features of Electronic Structure of Intermetallic Compounds CeNi<Subscript>4</Subscript>M (M = Fe,Co, Ni,Cu)

The evolution of the electronic structure of CeNi₄M (M = Fe, Co, Ni, Cu) intermetallics depending on the type of nickel substitutional impurity is explored. We have calculated band structures of these compounds and considered options of substituting one atom in nickel 3d sublattice in both types of crystallographic positions: 2c and 3g. The analysis of total energy self-consistent calculations has shown that positions of 2c type are more energetically advantageous for single iron and cobalt impurities, whereas a position of 3g type is better for a copper impurity. The Cu substitutional impurity does not change either the nonmagnetic state of ions or the total density at the Fermi level states. Fe and Co impurities, on the contrary, due to their considerable magnetic moments, induce magnetization of 3d states of nickel and cause significant changes in the electronic state density at the Fermi level.     

Comparative study of the core level photoemission of the ZrB2 and ZrB12

X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were used to investigate the binding energies and valence band for ZrB₂ and ZrB₁₂. The Zr 3d and B 1s core levels were identified. The Zr 3d core level shows a spin–orbit split 3d_5/2 and 3d_3/2 while that for B 1s core level exhibited a single symmetric peak, these being typical of zirconium and boride signals. Comparing the Zr 3d and B 1s core levels with metallic Zr, B₂O₃ and ZrO₂ reference materials only a negative chemical shift for Zr 3d associated to ZrB₂ was observed, which suggests that the charge transfer model based on the concept of electronegativity was not applicable to explain the superconductivity in the ZrB₁₂ sample. The measured valence band using UPS is consistent with the band-structure calculations indicating a higher density of states (DOS) at E_F for ZrB₁₂ respect to ZrB₂. Finally, we found that the weak mixed B-p and Zr-d states for ZrB₁₂ is crucial for the superconductivity due to the state population increased the DOS at the E_F.