Modern Physics Letters A

Quantum logic gates can perform calculations much more efficiently than their classical counterparts. However, the level of control needed to obtain a reliable quantum operation is correspondingly higher. In order to evaluate the performance of experimental quantum gates, it is therefore necessary to identify the essential features that indicate quantum coherent operation. In this paper, we show that an efficient characterization of an experimental device can be obtained by investigating the classical logic operations on a pair of complementary basis sets. It is then possible to obtain reliable predictions about the quantum coherent operations of the gate such as entanglement generation and Bell state discrimination even without performing these operations directly.

We study noncommutative field theories, which are inherently nonlocal, using a Poincaré-invariant regularisation scheme which yields an effective, nonlocal theory for energies below a cutoff scale. After discussing the general features and the peculiar advantages of this regularisation scheme for theories defined in noncommutative spaces, we focus our attention on the particular case when the noncommutativity parameter is inversely proportional to the square of the cutoff, via a dimensionless parameter η. We work out the perturbative corrections at one-loop order for a scalar theory with quartic interactions, where the signature of noncommutativity appears in η-dependent terms. The implications of this approach, which avoids the problems related to uv–ir mixing, are discussed from the perspective of the Wilson renormalisation program. Finally, we remark about the generality of the method, arguing that it may lead to phenomenologically relevant predictions, when applied to realistic field theories.

Parikh–Wilczek tunnelling framework is investigated again. We argue that Parikh–Wilczek's treatment, which satisfies the first law of black hole thermodynamics and consists with an underlying unitary theory, is only suitable for a reversible process. Due to the negative heat capacity, an evaporating black hole is a highly unstable system. That is, the factual emission process is irreversible, the unitary theory will not be satisfied and information loss is possible.

We investigate the single and pair production of new heavy leptons via string inspired E₆ model at future linear colliders. Signal and corresponding backgrounds for these leptons are studied. We have found that single production of heavy leptons is more relevant than that of pair production, as expected. For a maximal mixing value of 0.1, the upper mass limits of 2750 GeV in the single case and 1250 GeV in the pair production case are obtained at collider option.

We derive the statistical entropy of the Schwarzschild black hole by considering the asymptotic symmetry algebra near the boundary of the spacetime at past null infinity. Using a two-dimensional description and the Weyl invariance of black hole thermodynamics this symmetry algebra can be mapped into the Virasoro algebra generating asymptotic symmetries of anti-de Sitter spacetime. Using Lagrangian methods we identify the stress–energy tensor of the boundary conformal field theory and calculate the central charge of the Virasoro algebra. The Bekenstein–Hawking result for the black hole entropy is regained using Cardy's formula. Our result strongly supports a nonlocal realization of the holographic principle.

In a previous work it was shown that the radius of a nucleus R is determined by the α-cluster structure and can be estimated on the number of α-clusters disregarding the number of excess neutrons. A hypothesis was also made that the radius R_m of a β-stable isotope, which is actually measured at electron scattering experiments, is determined by the volume occupied by the matter of the core plus the volume occupied by the charge of the peripheral α-clusters. In this paper it is shown that the condition R_m = R restricts the number of excess neutrons filling the core to provide the β-stability. The number of peripheral clusters can vary from 1 to 5 and the value of R for heavy nuclei almost does not change, whereas the number of the excess neutrons should change with the number of peripheral clusters to provide the condition of R_m = R. It can explain the path of the β-stability and its width. The radii R_m of the stable isotopes with 12 ≤ Z ≤ 83 and the alpha-decay isotopes with 84 ≤ Z ≤ 116 that are stable to β-decay have been calculated.