Quantum Zeno effect: Quantum shuffling and Markovianity

The behavior displayed by a quantum system when it is perturbed by a series of von Neumann measurements along time is analyzed. Because of the similarity between this general process with giving a deck of playing cards a shuffle, here it is referred to as quantum shuffling, showing that the quantum Zeno and anti-Zeno effects emerge naturally as two time limits. Within this framework, a connection between the gradual transition from anti-Zeno to Zeno behavior and the appearance of an underlying Markovian dynamics is found. Accordingly, although a priori it might result counterintuitive, the quantum Zeno effect corresponds to a dynamical regime where any trace of knowledge on how the unperturbed system should evolve initially is wiped out (very rapid shuffling). This would explain why the system apparently does not evolve or decay for a relatively long time, although it eventually undergoes an exponential decay. By means of a simple working model, conditions characterizing the shuffling dynamics have been determined, which can be of help to understand and to devise quantum control mechanisms in a number of processes from the atomic, molecular and optical physics.Comment: 12 pages, 2 figure

N-2(+)((2)Sigma(g)) and Rb(S-2) in a hybrid trap: modeling ion losses from radiative association paths

By employing ab initio computed intermolecular potential energy surfaces we calculate the radiative association probabilities and rates for two different associative mechanisms involving trapped molecular ions N-2(+)((2)sigma(g)) interacting either directly with ultracold Rb atoms or undergoing charge-exchange (CE) processes leading to the formation of complexes of the strongly exothermic products N-2(X-1 sigma(g)) plus Rb+(S-1(0)). The two processes are expected to provide possible paths to ion losses in the trap within the timescale of experiments. The present calculations suggest that the associative rates for the vibrational' direct process are too small to be of any significant importance at the millikelvin temperatures considered in the experiments, while the vibronic' path into radiatively associating the CE products has a probability of occurring which is several orders of magnitude larger. However the reaction rate constants attributed to non-adiabatic CE [F. H. J. Hall and S. Willist, Phys. Rev. Lett., 2012, 109, 233202] are in turn several orders of magnitude larger than the radiative ones calculated here, thereby making the primary experimental process substantially unaffected by the radiative losses channel

A rigorous test of the statistical model for atom-diatom insertion reactions

The statistical model of atom-diatom insertion reactions was combined with CC capture theory. The resultant methodology was employed to calculate differential cross sections for the reactions of C(1D), N(2D), O(1D) and S(1D) with H2. A comparison of the resulting initial state-selected differential cross sections with the exact quantum reactive scattering calculations of Honvaultand Launay showed that all four reactions behave essentially statistically on their ground adiabatic potential energy surfaces

Quantum reactive scattering with a transmission-free absorbing potential.

A recently derived transmission-free absorbing potential is applied to the study of atom-diatom chemical reactions. This absorbing potential only depends on a single parameter--the width of the absorbing region--and its reflection properties are guaranteed to improve as this parameter is increased. Converged results can therefore be obtained very easily, as we illustrate with time-dependent wave packet calculations on the H + H2,F + H2, and H + O2 reactions

Dynamics of the D+^+ + H2_2 → HD + H+^+ Reaction at the Low Energy Regime by Means of a Statistical Quantum Method

The D+ +H2(v = 0, j = 0, 1) → HD+H+ reaction has been investigated at the low energy regime by means of a statistical quantum mechanical (SQM) method. Reaction probabilities and integral cross sections (ICSs) between a collisional energy of 10−4 eV and 0.1 eV have been calculated and compared with previously reported results of a time independent quantum mechanical (TIQM) approach. The TIQM results exhibit a dense profile with numerous narrow resonances down to Ec ∼ 10−2 eV and for the case of H2(v = 0, j = 0) a prominent peak is found at ∼2.5 × 10−4 eV. The analysis at the state-to-state level reveals that this feature is originated in those processes which yield the formation of rotationally excited HD(v′ = 0, j′ > 0). The statistical predictions reproduce reasonably well the overall behaviour of the TIQM ICSs at the larger energy range (Ec ⩾ 10−3 eV). Thermal rate constants are in qualitative agreement for the whole range of temperatures investigated in this work, 10-100 K, although the SQM values remain above the TIQM results for both initial H2 rotational states, j = 0 and 1. The enlargement of the asymptotic region for the statistical approach is crucial for a proper description at low energies. In particular, we find that the SQM method leads to rate coefficients in terms of the energy in perfect agreement with previously reported measurements if the maximum distance at which the calculation is performed increases noticeably with respect to the value employed to reproduce the TIQM results

Quantum mechanical study of the proton exchange in the ortho-para H-2 conversion reaction at low temperature

International audienc

Quantum mechanical study of the proton exchange in the ortho-para H-2 conversion reaction at low temperature

International audienc