International Journal of Modern Physics B

Quantum control strategy is discussed from the perspective of quantum information. First, the constraints imposed on quantum control by quantum theory are analyzed. Then some quantum control schemes based on quantum information are discussed, such as teleportation-based distant quantum control, quantum feedback control using quantum cloning and state recognition, quantum control based on measurement and Grover iteration. Finally, some applications of quantum control theory in quantum information and quantum computation such as quantum error correction coding, universality analysis of quantum computation, feedback-induced entanglement enhancement, etc., are presented and the potential applications of quantum control are also prospected.

We calculate zeros of the q-state Potts model partition function Z(G_Λ,q,v) for large q, where v is the temperature variable and G_Λ is a section of a lattice Λ with coordination number κ_Λ and various boundary conditions. Lattice types studied include square, triangular, honeycomb, and kagomé. We show that for large q these zeros take on approximately circular patterns in the complex x_Λ plane, where x_Λ=v/q^2/κ_Λ. This generalizes a known result for the square lattice to the other lattices considered.

Coupled chaotic oscillators are found to be able to achieve the partial synchronization state in some networks. The scaling relation between the synchronization time and the coupling at the synchronous threshold is found and explained. In the studies, it was found that the coupling of the synchronization properties of networks is not homogeneous.

Here we study the dimerized spin ladder with nearest-neighbor (J₁) and next-nearest-neighbor (J₂) anti-ferromagnetic interaction under a magnetic field. We predict the existence of different magnetization plateaus for the presence of spin-Peierls interaction on both J₁ and J₂. Magnetization plateau at m = 0 for J₁ dimerization is spontaneous due to XY interaction, but it is absent for J₂ dimerization, only intrinsic umklapp term leads to plateau (spin gap) state for some specific values of XXZ anisotropy (Δ) and J₂. Here we predict a saturation plateau which is the classical phase of the system. There are some numerical support of our analytical approach already existing in the literature. The transition from commensurate gapped phase to incommensurate Luttinger liquid phase is the Mott-δ type of transition.

This paper demonstrates in theory that a bias-induced oscillatory current should occur in a tunneling junction made of the high-T_c cuprates in pseudogap state. This novel oscillatory effect can be utilized for the judging mechanism of pseudogap in the high-T_c cuprates and a series of non-superconducting materials. In application, this novel effect can be utilized for making electronic devices, using Cooper pairs and operating at room temperature.

XPS core level measurements are used to observe the surface changes in amorphous thin films of mixed oxides In₂O₃–SnO₂ system deposited by co-evaporation. The effects of changes in composition (in mol%), film thickness, substrate temperature, post-deposition annealing, and etching with Ar⁺ ions on the binding energies of In(3d) and Sn(3d) doublets in mixed oxides In₂O3–SnO₂ system are presented. XPS core level In(3d) and Sn(3 d) spectra at various compositions exhibit the characteristic 3d_{5 / 2} and 3d_{3 / 2} doublets. The positions of the In(3d) and Sn(3d) lines are those as expected for In³⁺ ions in In₂O₃ and Sn⁴⁺ ions in SnO₂. The initial decrease in binding energy with an increase in Sn content in In₂O₃ lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The increase in binding energy above the critical Sn content (10 mol% SnO₂) is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The decrease in binding energy with film thickness is caused by the increase in free-carriers density, which is generated by oxygen vacancy acting as two electrons donor. The decrease in binding energy with a substrate and annealing temperatures is due either to the severe deficiency of oxygen, which deteriorates the film properties and reduces the mobility of the carriers or to the diffusion of Sn atoms from interstitial locations into the In cation sites and the formation of indium and tin species of lower valence states so that the In³⁺ and the Sn⁴⁺ oxidation states may be changed to the In²⁺ and the Sn²⁺ oxidation states respectively. The new oxidation states, In²⁺ and Sn²⁺, formed due to ion etching and annealing the samples can be attributed to the internal electron transfer from oxygen 2p to the In 5s and Sn 5s levels both in In₂O₃ and SnO₂.

In this paper we discuss the solutions of the cubic nonlinear Schrödinger equation with variable coefficients that model a trapped, quasi-one-dimensional Bose–Einstein condensate with time-varying potential and time-varying atomic scattering length. By applying the theory of Jacobian elliptic functions, we propose a new ansatz to find two new families of solutions. We also obtained regions in the parameters space in which the found families of solutions exist.

This work presents the results of the resistivity vs. temperature measurements obtained under different excitation currents, carried out on Nd_1.783Ce_0.15CuO_3.989 followed by the new analytical formula Nd_{2-(4x + v-2)/3}Ce_0.15 CuO_y. The measurements revealed different characteristics for different parts of the investigated sample. The obtained results may suggest the idea that double resistive superconducting transition in n-type polycrystalline cuprates is of a rather extrinsic future. The electron microscope photography applied in order to investigate the microstructure of the chosen samples also supported the above view.

This paper describes the development of a new processing technology for rotational moulding of wollastonite microfibre (WE) reinforced polyethylene (PE). Manufacturing wollastonite-polyethylene composites involved blending, compounding by extrusion, and granulating prior to rotational moulding. The properties of the resulting composites were characterised by tensile and impact strength measurements. The results show that tensile strength increases monotonically with the addition of wollastonite fibres, but impact strength is decreased. In addition, the processability is also decreased after adding more than 12 vol% WE because of increased viscosity. The effects of a coupling agent, maleated polyethylene (MAPE), on the mechanical performance and processability were also investigated. SEM analysis reveals good adhesion between the fibre reinforcements and polyethylene matrix at the fracture surface with the addition of MAPE. It is proposed that fillers with small particles with high aspect ratio (such as wollastonite) provide a large interfacial area between the filler and the polymer matrix, and may influence the mobility of the molecular chains.

Motivated by a recent experiment on Bloch oscillation of Bose–Einstein condensates (BEC) in accelerated optical lattices, we consider the Josephson dynamics of a BEC in an accelerated double-well potential. We show that acceleration suppresses coherent population / phase oscillation between the two wells. Accelerating the double-well renders the Josephson coupling energy E_J time-dependent and this emerges as a source of dissipation. This dissipative mechanism helps to stabilize the system. The results are used to interpret a recent experimental result (M. Jona-Lasinio, O. Morsh, M. Cristiani E. Arimonod and C. Menotti, cond-mat / 0501572).

The magnetic properties of a mixed spin-2 and spin-5 / 2 Heisenberg ferrimagnetic system on a layered honeycomb lattice are investigated theoretically by a multisublattice Green-function technique which takes into account the quantum nature of Heisenberg spins. We calculate the magnetization and the compensation temperature and transition temperature of the system in an external magnetic field and in a zero external magnetic field, and find that the transition temperature of the system increases on the effect of an external magnetic field, the compensation point disappears when the single-ion anisotropy is not large and there are two compensation points when the anisotropy is large. We also calculate the initial susceptibilities of the system.

The density functional theory for the freezing hard spheres is studied. We use a variety of the hard sphere direct correlation functions (DCFs) such as the one introduced by Roth et al. [J. Phys. Condens. Matter14, 12063 (2002)]; we call it RELK DCF, a new hard sphere DCF developed here by a combination of the RELK and the Percus–Yevick DCFs, and finally the generalized mean spherical approximation (GMSA). The structure factor, the freezing, and order parameters are calculated using these DCFs. The structure factor obtained by the new DCF is in good agreement with the Monte Carlo simulation. The best result for the freezing parameters in comparison with the Monte Carlo simulations is obtained by using our new expression for the DCF. Finally we obtain the Helmholtz free energy of the hard sphere FCC crystals using modified weighted density approximation (MWDA), and again the best results are obtained by using the new expression for the hard sphere DCF.

In a case study, the exact solution of a self-consistent Langevin equation associated with a nonlinear Fokker–Planck equation is derived. On the basis of this solution, a Monte Carlo simulation scheme for the Langevin equation is proposed. The case study addresses a generalized geometric Brownian walk that describes the collective dynamics of a large set of interacting stocks. Numerical results obtained from the Monte Carlo simulation are compared with analytical solutions derived from the nonlinear Fokker–Planck equation. The power of the Monte Carlo simulation is demonstrated for situations in which analytical solutions are not available.