E. Bene

Reciprocity in the degeneracies of some tetra-atomic molecular ions

Various ab initio computations, as, e.g., in G. J. Halász and Á. Vibók, Int. J. Quantum Chem. 111, 342 (2011), have shown that in molecules of the type (HCCH)(+), when the extremal H atoms are distorted from a linear form but maintain a planar geometry, a pair of conical intersections (ci) occur at such positions that the ratios of the distortional coordinates of the two atoms are in the two cis reciprocals of each other. These computations have here been extended to locate the cis also for HCNH. The two groups of results are explained by simple analytic perturbational expressions for the energy differences of the lowest adjacent electronic states, with inclusion of excited state effects.

Two-qubit Bell inequality for which positive operator-valued measurements are relevant

A bipartite Bell inequality is derived which is maximally violated on the two-qubit state space if measurements describable by positive operator valued measure (POVM) elements are allowed, rather than restricting the possible measurements to projective ones. In particular, the presented Bell inequality requires POVMs in order to be maximally violated by a maximally entangled two-qubit state. This answers a question raised by N. Gisin [in Quantum Reality, Relativistic Causality, and Closing the Epistemic Circle: Essays in Honour of Abner Shimony, edited by W. C. Myrvold and J. Christian (Springer, The Netherlands, 2009), pp. 125-138].

Lower bound on the communication cost of simulating bipartite quantum correlations

Suppose Alice and Bob share a maximally entangled state of any finite dimension and each perform two-outcome measurements on the respective part of the state. It is known, due to the recent result of Regev and Toner, that if a classical model is augmented with two bits of communication, then all the quantum correlations arising from these measurements can be reproduced. Here, we show that two bits of communication are in fact necessary for the perfect simulation. In particular, we prove that a pair of maximally entangled four-dimensional quantum systems cannot be simulated by a classical model augmented by only one bit of communication.

Measurement incompatibility does not give rise to Bell violation in general

In the case of a pair of two-outcome measurements incompatibility is equivalent to Bell nonlocality. Indeed, any pair of incompatible two-outcome measurements can violate the Clauser-Horne-Shimony-Holt Bell inequality, which has been proven by Wolf et al. [Phys. Rev. Lett. 103, 230402 (2009)]. In the case of more than two measurements the equivalence between incompatibility and Bell nonlocality is still an open problem, though partial results have recently been obtained. Here we show that the equivalence breaks for a special choice of three measurements. In particular, we present a set of three incompatible two-outcome measurements, such that if Alice measures this set, independent of the set of measurements chosen by Bob and the state shared by them, the resulting statistics cannot violate any Bell inequality. On the other hand, complementing the above result, we exhibit a set of

Bounding the persistency of the nonlocality of W states

N

Qutrit witness from the Grothendieck constant of order four

measurements for any

Theoretical study of charge exchange dynamics in He+ + NO collisions

N>2

Quasiclassical Trajectory Studies of the Dynamics of Bimolecular Reactions of Vibrationally Highly Excited Molecules

that is

Comparison between anion and cation emission from CH4 molecules colliding with 10.5-keV C+ ions: Fragment-energy aspects

(N-1)

Anion emission from water molecules colliding with positive ions: Identification of binary and many-body processes

-wise compatible, nevertheless it gives rise to Bell violation.