160 research outputs found
Collisional Quenching at Ultralow Energies: Controlling Efficiency with Internal State Selection
Calculations have been carried out for the vibrational quenching of excited
H molecules which collide with Li ions at ultralow energies. The
dynamics has been treated exactly using the well known quantum coupled-channel
expansions over different initial vibrational levels. The overall interaction
potential has been obtained from the calculations carried out earlier in our
group using highly correlated ab initio methods. The results indicate that
specific features of the scattering observables, e.g. the appearance of
Ramsauer-Townsend minima in elastic channel cross sections and the marked
increase of the cooling rates from specific initial states, can be linked to
potential properties at vanishing energies (sign and size of scattering
lengths) and to the presence of either virtual states or bound states. The
suggestion is made that by selecting the initial state preparation of the
molecular partners, the ionic interactions would be amenable to controlling
quenching efficiency at ultralow energies
Ion chemistry in the early universe: revisiting the role of HeH+ with new quantum calculations
The role of HeH+ has been newly assessed with the aid of newly calculated
rates which use entirely ab initio methods, thereby allowing us to compute more
accurately the relevant abundances within the global chemical network of the
early universe. A comparison with the similar role of the ionic molecule LiH+
is also presented. Quantum calculations have been carried out for the gas-phase
reaction of HeH+ with H atoms with our new in-house code, based on the negative
imaginary potential method. Integral cross sections and reactive rate
coefficients obtained under the general conditions of early universe chemistry
are presented and discussed. With the new reaction rate, the abundance of HeH+
in the early universe is more than one order of magnitude larger than in
previous studies. Our more accurate findings further buttress the possibility
to detect cosmological signatures of HeH+.Comment: Astronomy and Astrophysics, in pres
Quantum Correlation Bounds for Quantum Information Experiments Optimization: the Wigner Inequality Case
Violation of modified Wigner inequality by means binary bipartite quantum
system allows the discrimination between the quantum world and the classical
local-realistic one, and also ensures the security of Ekert-like quantum key
distribution protocol. In this paper we study both theoretically and
experimentally the bounds of quantum correlation associated to the modified
Wigner's inequality finding the optimal experimental configuration for its
maximal violation. We also extend this analysis to the implementation of
Ekert's protocol
Reply to Comment on "Quantum dense key distribution"
In this Reply we propose a modified security proof of the Quantum Dense Key
Distribution protocol detecting also the eavesdropping attack proposed by
Wojcik in his Comment.Comment: To appear on PRA with minor change
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