The action of transformations of the point group of a molecule on its instantaneous nuclear configuration

The action of the transformations of a point group of a rigid molecule in a specified electronic state on the instantaneous nuclear configuration of the molecule is considered. This action is shown to be equivalent to permutations of identical nuclei in the effective potential of interaction of the nuclei in this state, which is invariant with respect to the transformations of the point group. Therefore, the point group characterizing the electronic state should be used as the rigorous symmetry group of the total electronic-vibrational-rotational motion.     

Electronic spin susceptibility of metallic superconductive nano-particles

We have observed the thermodynamic properties of metallic superconductive nano-particles in the grand canonical ensemble; and the level distribution and the level correlation between the discrete electronic energy levels are considered in the calculation of the electronic spin susceptibility of the ensemble numerically. The quantum effect, even--odd effect and other special effects existing in the metallic nano-particles are also studied in this article.     

Towards a semi-classical approximation of the non-linear σ-model

We consider the contribution of instantons of arbitrary topological charge to the expectation value of any observable in the CP¹ model defined on the sphere S².We replace the integration over one of the parameters of the instantons by an integration over the group of isospin transformations and carry it out explicitly by using the isospin invariance. This allows us to express the result as the expectation value of an observable of a neutral gas of 2 species of particles, computed in the grand canonical ensemble. The interactions are complicated and involve multi-body forces (2 × k, k being the topological charge).     

超小金属粒子的热力学性质

超小金属粒子系综的热力学性质受到分离电子能级分布和能级关联的影响。在考虑能级统计后，数值计算了含有奇数或偶数个电子的超小金属粒子正则系综的电子比热和自旋磁化率，并讨论了其低温和高温特征。作为例子，本文数值纳米铝粒子的电子比热和自旋磁化率。     

Hybrid quantum circuit with a superconducting qubit coupled to a spin ensemble

We report the experimental realization of a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins. The qubit, of the transmon type, is coherently coupled to the spin ensemble consisting of nitrogen-vacancy centers in a diamond crystal via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare a superposition of the qubit states that we store into collective excitations of the spin ensemble and retrieve back into the qubit later on. These results constitute a proof of concept of spin-ensemble based quantum memory for superconducting qubits.     

Energy dependence on fractional charge for strongly interacting subsystems

The energies of a pair of strongly interacting subsystems with arbitrary noninteger charges are examined from closed- and open-system perspectives. An ensemble representation of the charge dependence is derived, valid at all interaction strengths. Transforming from resonance-state ionicity to ensemble charge dependence imposes physical constraints on the occupation numbers in the strong-interaction limit. For open systems, the chemical potential is evaluated using microscopic and thermodynamic models, leading to a novel correlation between ground-state charge and an electronic temperature.     

Structural fluctuations in ensembles of nanoparticles

Caused by the interaction between the particles, structural fluctuations influence thermodynamics and order of transformation of an ensemble of nanoparticles. A stringed thermodynamic analysis revealed that, in fluctuating ensembles, the ratio of particle numbers in the equilibrium over the one in the non-equilibrium phase is independent of any metastable in between. Structural transformations in such ensembles, connected to latent heat, are of infinite order. These findings are summarized in a set of theorems ruling structural fluctuations. Finally, the consequences of fluctuations are demonstrated by an example.     

Effects of spin interactions in disordered electronic systems: Loop expansions and exact relations among local gauge invariant models

Spindependent ensembles for disordered electronic systems are examined in the region of extended states. We derive relations between spindependent and previously studied spinless ensembles. We prove that these relations are valid in all orders of a graph theory, on the basis of which we propose them to be exact. These exact relations and supplementary two loop order calculations in 2+ dimensions are used to reveal the existence of universality classes for the critical behaviour at the mobility edges. The mobility edge behaviour of a spindependent ensemble with real (random) hopping agrees with that of the spinless phase invariant ensemble except for a crossover to the real matrix ensemble in the limit of vanishing spinflip amplitudes. Anomalous properties in the band center are also discussed. We derive a transformation which maps arbitrary correlation functions of a complex spindependent ensemble into those of the real matrix ensemble. This relation implies the absence of a mobility edge for the complex spindependent ensemble within the validity region of the theory.     

Entanglement transformation between ensembles of three-qubit GHZ-type states by LOCC

We present a novel method to verify whether an ensemble of three-qubit GHZ-type state could be transformed to another one by local operations and classical communication (LOCC). This result highlights intriguing similarity compared with the case in the transformation between two ensembles of two-qubit states. Our approach may provide a splendid insight into the transformations between two general multipartite states.     

Quantum Spin Hall Effect in a Triple-Well Quantum Dot System

A scheme for generating a quantum spin Hall effect for an ensemble of electrons trapped in a triple-well quantum dot system is proposed. Light-induced effective spin-dependent gauge potential and gauge filed are both given in a real Gaussian pulses space. In our scheme, the spin Hall effect can be demonstrated by electronic population without spin-orbit coupled interaction in the absence of any magnetic fields.     

Universal conductance fluctuations in Sierpinski carpets

We theoretically investigate the conductance fluctuation of two-terminal device in Sierpinski carpets. We find that, for the circular orthogonal ensemble (COE), the conductance fluctuation does not display a universal feature; but for circular unitary ensemble (CUE) without time-reversal symmetry or circular symplectic ensemble (CSE) without spin-rotational symmetry, the conductance fluctuation can reach an identical universal value of 0.74±0.01(e²/h). We further find that the conductance distributions around the critical disorder strength for both CUE and CSE systems share the similar distribution forms. Our findings provide a better understanding of the electronic transport properties of the regular fractal structure.     

Entanglement constrained by superselection rules

Bipartite entanglement may be reduced if there are restrictions on allowed local operations. We introduce the concept of a generalized superselection rule to describe such restrictions, and quantify the entanglement constrained by it. We show that ensemble quantum information processing, where elements in the ensemble are not individually addressable, is subject to the superselection rule associated with the symmetric group (the group of permutations of elements). We prove that even for an ensemble comprising many pairs of qubits, each pair described by a pure Bell state, the entanglement per element constrained by this superselection rule goes to zero for a large number of elements.     

New infinite-dimensional symmetry groups for the stationary axisymmetric Einstein--Maxwell equations with multiple Abelian gauge fields

The so-called extended hyperbolic complex (EHC) function method is used to study further the stationary axisymmetric Einstein--Maxwell theory with $p$ Abelian gauge fields (EM-$p$ theory, for short). Two EHC structural Riemann--Hilbert (RH) transformations are constructed and are then shown to give an infinite-dimensional symmetry group of the EM-$p$ theory. This symmetry group is verified to have the structure of semidirect product of Kac--Moody group $\widehat{SU(p+1,1)}$ and Virasoro group. Moreover, the infinitesimal forms of these two RH transformations are calculated and found to give exactly the same infinitesimal transformations as in previous author's paper by a different scheme. This demonstrates that the results obtained in the present paper provide some exponentiations of all the infinitesimal symmetry transformations obtained before.     

Effect of spin and charge fluctuations on the electronic structure of ferromagnetic compounds based on rare-earth metals (on an example of EuO)

The influence of spin and charge density fluctuations on the electronic structure is studied for the generalized fd-model. It is demonstrated that these fluctuations lead to electronic spectrum transformation and redistribution of electrons between f- and d-states, thereby giving rise to electronic phase transformations. It is established that these phenomena are observed in ferromagnetic and paramagnetic regions. A detailed analysis is performed on an example of the EuO ferromagnetic semiconductor.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 100–104, October, 2004.     

Configurational electronic entropy and the phase diagram of mixed-valence oxides: the case of LixFePO4

We demonstrate that configurational electronic entropy, previously neglected, in ab initio thermodynamics of materials can qualitatively modify the finite-temperature phase stability of mixed-valence oxides. While transformations from low-T ordered or immiscible states are almost always driven by configurational disorder (i.e., random occupation of lattice sites by multiple species), in FePO4-LiFePO4 the formation of a solid solution is almost entirely driven by electronic rather than ionic configurational entropy. We argue that such an electronic entropic mechanism may be relevant to most other mixed-valence systems.     

Strong coupling of a spin ensemble to a superconducting resonator

We report the realization of a quantum circuit in which an ensemble of electronic spins is coupled to a frequency tunable superconducting resonator. The spins are nitrogen-vacancy centers in a diamond crystal. The achievement of strong coupling is manifested by the appearance of a vacuum Rabi splitting in the transmission spectrum of the resonator when its frequency is tuned through the nitrogen-vacancy center electron spin resonance.     

Calculation of the Probabilities of Molecular Transitions in Modeling Interisomeric Structural Transformations

The problems of a computational procedure in modeling structural isomer–isomer transitions in multiatomic molecules are considered. A number of approximations that allow one to considerably simplify calculation of the probabilities of these transformations are suggested. In comparison with traditional calculations of potential surfaces and determination of their saddle points, in the proposed approach the relationship between the electronic and vibrational components of a general problem is virtually changed. A particular emphasis is put on the vibrational part, which seems to be more physical. It is shown that the problem of structural isomer–isomer conversions can be solved without resorting at all to explicit calculation of the contribution of an electronic matrix element to the probability of transition. There is no need to study in detail the shapes of potential surfaces; it suffices only to know the positions of their minima. The calculation of multidimensional vibrational integrals is replaced by calculation of one-dimensional integrals. The results obtained form a basis for constructing methods for modeling the dynamic spectra of complex molecules considering their structural transformations.     

Method for computing the electronic structure of thin crystalline films with disordered surface atoms

We present a Green's function method for computing the electronic structure of a crystalline film in which the surface atoms are disordered. The disorder is taken into account by considering an ensemble of random displacement configurations. We use a uninodal approximation to construct a general formalism for the method and obtain a determinant equation and expression for the density of states, permitting a numerical solution to the spectral problem. We discuss which features of the surface electronic structure are due to displacement disorder in the surface region of the crystal, and in what systems such disorder can be realized.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 81–88, August, 1988.We thank G. V. Vol'f for some useful discussions.     

Direct STM observation of electronic structure modification of naphthacenequinone molecules due to photoisomerization

Light-induced conformational transformations of the naphthacenequinone (NQ) molecules are observed by scanning tunneling microscopy (STM). NQ molecules packed in a Langmuir-Blodgett (LB) film are shown to form stable ordered structures on a surface of highly oriented pyrolytic graphite (HOPG). The local density of electronic states is found to exhibit the distinct peak which is characteristic of two-dimensional conductivity. An additional subband of empty electronic states is found for NQ molecules in form A but not in form B. The constant-height STM images of individual molecules in form A demonstrate an additional structure that is indicative of a conformational transition of the NQ molecules. This transition involves the transfer of the phenoxy group from one oxygen to another. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 486–490 (25 September 1998)