Exact critical exponents for quantum spin chains,non-linear σ-models at θ=π and the quantum hall effect

We use non-abelian bosonization to predict critical exponents for quantum chains of arbitrary spin and arbitrary symmetry SU(n). Passing to the large representation limit gives non-linear σ-models on the manifolds U(2n)/U(n)×U(n) at topological angle θ=π. For n=1 this is the familiar “O(3)” model; taking the replica limit n→0 given critical exponents for the localization transition in the quantum Hall effect. Given certain assumptions, these exponents should be exact.     

Phase differences between quantum oscillations of the magnetoresistance and the hall effect in Hg1−xMnxTe and Hg1−xCdxTe

A Landau-level broadening-dependent phase shift has been observed between the Shubnikovde Haas oscillations of the magnetoresistance and the Hall effect in a series of Hg_1−xMn_xTe and Hg_1−xCd_xTe samples. The phase shift varies between 0 and 90° and appears not to be influenced by the exchange interaction between the Mn²⁺ ions and the carriers. The results are in good agreement with the theoretical predictions for short range scattering potentials.     

A bridge between acoustic metamaterials and quantum computation

Acoustic waves are one necessary ingredient for many useful tasks.To complete these tasks,acoustic waves need to be transmitted in certain ways,and sometimes,people would like them to be transmitted in ways that are unnatural through passive devices.The latter seemingly unrealistic wish became true with the advent of acoustic metamaterials,which sunrises people very much.Acoustic metamaterials are artificial materials made of well-designed microstructures[1].     

Competition between hydrogen bond and σ-hole interaction in SCS-HArF and SeCSe-HArF complexes

A computational study of the complexes formed between HArF and XCX (X?=?O, S, and Se) has been performed at the MP2/aug-cc-pVTZ level. Two types of complexes were found. One is formed through a hydrogen bond with XCX as the electron donor and the other is formed through the σ-hole interaction with XCX as the electron acceptor. The OCO-FArH complex is more stable than the OCO-HArF complex, whereas the XCX-HArF (X?=?S and Se) complex is more stable than the XCX-FArH complex. The distant H-Ar bond is shortened and exhibits a blue shift, but the associated one displays a red shift in SCS-HArF and SeCSe-HArF complexes. When compared with XCX-HF complex, the structure of the complex suffers a great effect from the inserted noble gas atom. The natural bond orbital (NBO) and atoms in molecules (AIM) have been performed for a better understanding of the interactions.     

Complementarity between quantum coherence and mixedness:a majorization approach

Quantum coherence is a relevant resource for various quantum information processing tasks, but it is fragile since it is generally affected by environmental noise. This is reflected in the loss of purity of the system, which in turn limits the amount of quantum coherence of it. As a consequence, a complementarity relation between coherence and mixedness arises. Previous works characterize this complementarity through inequalities between the ?₁-norm of coherence and linear entropy, an...     

Relationship between normalized light intensity and attenuated total reflection ratio

Attenuated total reflection(ATR)ratio is usually utilized to study the properties of surface plasmon res- onance(SPR)sensors.The relationship between normalized light intensity and ATR ratio is investigated, and a modification coefficient is put forward to describe the relationship.A mathematical expression is built up for the coefficient based on Fresnel principle.The result shows that the ATR ratio,which cannot be measured directly in experiments,can be determined with the coefficient and the normalized intensity of light.The characteristic of the coefficient is also discussed.     

The relation between the generalised Eshelby integral and the generalised BCS and DB models

The generalised BCS dislocation group model and the generalised DB atomic cohesive force zone model have obtained the same results on nonlinear fracture study of some one-,two-and three-dimensional quasicrystals.This work reveals some inherent connection between the two models,and finds that their common basis is the generalised Eshelby integral based on the generalised Eshelby energy-momentum tensor for quasicrystals.Further applications of the theory in solving nonlinear fracture problems of the materials are also discussed.     

Critical behaviour of SU(n) quantum chains and topological non-linear σ-models

The critical behaviour of SU(n) quantum “spin” chains, Wess-Zumino-Witten σ-models and grassmanian σ-models at topological angle θ = π (of possible relevance to the quantum Hall effect) is reexamined. It is argued that an additional Z_n symmetry is generally necessary to stabilize the massless phase. This symmetry is not present for the σ-models for n > 2 and is only present for certain representations of “spin” chains.     

Nonradiative and radiative Förster energy transfer between quantum dots

We theoretically study nonradiative and radiative energy transfer between two localized quantum emitters, a donor (initially excited) and an acceptor (receiving the excitation). The rates of nonradiative and radiative processes are calculated depending on the spatial and spectral separation between the donor and acceptor states and for different donor and acceptor lifetimes for typical parameters of semiconductor quantum dots. We find that the donor lifetime can be significantly modified only due to the nonradiative Förster energy transfer process at donor–acceptor separations of approximately 10 nm (depending on the acceptor radiative lifetime) and for the energy detuning not larger than 1–2 meV. The efficiency of the nonradiative Förster energy transfer process under these conditions is close to unity and decreases rapidly with an increase in the donor–acceptor distance or energy detuning. At large donor–acceptor separations greater than 40 nm, the radiative corrections to the donor lifetime are comparable with nonradiative ones but are relatively weak.     

GaAsδ-doped quantum wire superlattice characterization by quantum Hall effect and Shubnikov–de Haas oscillations

Quantum wire superlattices (1D) realized by controlled dislocation slipping in quantum well superlattices (2D) (atomic saw method) have already shown Magneto-phonon oscillations. This effect has been used to investigate the electronic properties of such systems and prove the quantum character of the physical properties of the wires. By cooling the temperature and using pulsed magnetic field up to 35 T, we have observed both quantum Hall effect (QHE) and Shubnikov–de Haas (SdH) oscillations for various configurations of the magnetic field. The effective masses deduced from the values of the fundamental fields are coherent with those obtained with Magneto-phonon effect. The field rotation induces a change in the resonance frequencies due to the modification of the mass tensor as in a (3D) electron gas. In view the QHE, the plateaus observed in ρ_YZare dephased relatively toρ_ZZ minima which seems to be linked to the dephasing of the minima of the density of states of the broadened Landau levels.     

Feynman path integral with underlying noncommutative “geometry” and quantum mechanics in external field

Noncommutative algebra of translations as a deforming commutative algebra induces a linear vector potential in the plane. This potential perturbs the generators of translations. Such potential we can identify, for example, with constant magnetic or with homogeneous electric fields. This potential introduces an extra phase factor in the Feynman formulation of quantum mechanic.Presented at the Colloquium on the Quantum Groups, Prague, 18–20 June 1992.     

The path integral on the Poincaré upper half plane and for Liouville quantum mechanics

We present a rigorous path integral treatment of free motion on the Poincaré upper half plane. The Poincaré upper half plane, as a riemannian manifold, has recently become important in string theory and in the theory of quantum chaos. The calculation is done by a time-transformation and the use of the canonical method for determining quantum corrections to the classical lagrangian. Furthermore, we shall show that the same method also works for Liouville quantum mechanics. In both cases, the energy spectrum and the normalized wavefunctions are determined.     

Relationship between positron bulk lifetime and lattice constants-research on NaCl-type crystals

The positron lifetimes of some compounds with NaCl-type crystal structure are calculated with the method of atomic superposition approximation (ATSUP) based on the theories of local-density-approximation (LDA) and generalgradient-approximation (GGA).The systematical results are fitted to a curve as a function of lattice constants.The positron bulk lifetimes of some other compounds with NaCl-type crystal structure,which are deduced from the systematical results,are in agreement with the experimental results given in other literature.     

Remote interactions between two d-dimensional distributed quantum systems： nonlocal generalized quantum control-NOT gate and entanglement swapping

We present a systematic simple method to implement a generalized quantum control-NOT （CNOT） gate on two d-dimensional distributed systems. First, we show how the nonlocal generalized quantum CNOT gate can be implemented with unity fidelity and unity probability by using a maximally entangled pair of qudits as a quantum channel. We also put forward a scheme for probabilistically implementing the nonlocal operation with unity fidelity by employing a partially entangled qudit pair as a quantum channel. Analysis of the scheme indicates that the use of partially entangled quantum channel for implementing the nonlocal generalized quantum CNOT gate leads to the problem of ＇the general optimal information extraction＇. We also point out that the nonlocal generalized quantum CNOT gate can be used in the entanglement swapping between particles belonging to distant users in a communication network and distributed quantum computer.[第一段]     

A relation between instantons of grassmann σ-models and Toda equations: II

We construct special solutions of Toda equations and show that these are deeply related with irreducible representations of sl(2;). We also show that after taking a continuum limit of Toda equations, these become the well-known solution of the continuum Toda equation.Partially supported by the Grant-in-Aid for Scientific Research, No. 03640085.     

Wannier–Stark effect in strongly coupled three quantum well structures and superlattices

The Wannier–Stark effect has been investigated in strongly coupled three quantum well structures and 23.5 period superlattices consisting of 25Å wide GaAs wells separated by Al_0.25Ga_0.75As barriers of the same width. A blue shift associated with the Wannier–Stark localization of heavy holes states is observed for the first time, followed by a second blue shift at higher electric fields due to the electron localization. This is contrary to the widely reported single blue shift of the order of (e+hh)/2, where e and hh are the electron and heavy hole miniband widths respectively, produced by Wannier–Stark localization in superlattices.