The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics

The well-established and rapidly expanding field of molecular processes in excited systems, facilitated by the use of light sources, garners significant research interest from numerous experimental and theoretical groups worldwide. This highly interdisciplinary field establishes extensive connections with atomic, molecular and optical physics, astrophysics, biophysics, physical chemistry, solid-state physics and even molecular biology. The present topic provides an advanced overview of research activities in cutting-edge areas such as ultrafast lasers, nanoscale systems, atomic and molecule collisions on surfaces and molecular photofragmentation processes. The contributions to this subject encompass experimental, theoretical and computational studies conducted both at the fundamental level, exploring elementary mechanisms, and at a more applied level, addressing the requirements of diverse applications in nanotechnology and materials science.

Metastable ion Coulomb crystal (ICC) in the polychromatic optical superlattice (OSL) created by so-called rectified gradient forces is studied. Our analysis is based on the numerical solution of the nonlinear stochastic differential equations taking into account the trapping and dissipative forces, their quantum fluctuations, and Coulomb repulsion of ions. The key question is how long will this metastable highly ordered crystalline structure persist. The critical parameter determining the ICC destruction times td is the OSL period L (at fixed intensity values of the optical fields). Our simulations demonstrate that td of the ICC, consisting of several tens of mercury ions, experiences giant changes (by four orders of magnitude) at relatively slight variations of the optical superlattice period L in the range from 0.35 to 0.70 mm. We have shown that the dependence td (L) can be approximated by the Arrhenius-like equation with an effective activation energy which is nonlinearly dependent on the OSL period L. These results explain the ultrahigh sensitivity td (L) to the OSL period L and show how to adjust L to ensure all-optical confinement of ICC in the OSL from a fraction of a second to one and half minutes.

We consider the noisy thermal amplifier channel, where signal modes are amplified together with environmental thermal modes. We focus on the secret-key capacity of this channel, which is the maximum amount of secret bits that two remote parties can generate by means of the most general adaptive protocol, assisted by unlimited and two-way classical communication. For this channel only upper and lower bounds are known, and in this work we improve the lower bound. We consider a protocol based on squeezed states and homodyne detections, in both direct and reverse reconciliation. In particular, we assume that trusted thermal noise is mixed on beam splitters controlled by the parties in a way to assist their homodyne detections. The new improved lower bounds to the secret-key capacity are obtained by optimizing the key rates over the variance of the trusted noise injected, and the transmissivity of the parties’ beam splitters. Our results confirm that there is a separation between the coherent information of the thermal amplifier channel and its secret key capacity.

Radiative lifetimes of 19 selected W II levels with energies between 36 000 cm-1 and 55 000 cm-1 have been measured with the time-resolved laser-induced fluorescence technique. The ions are generated in a hollow cathode discharge and stored in a linear Paul trap. Selected states are populated with tunable dye laser pulses and the subsequent fluorescence is measured by means of a 5 Gigasample transient digitizer and a fast photodetector with a risetime of 700 ps. By taking into account both the temporal profile of the laser pulses and the separately measured response function of the system, the lifetime can be determined from the full decay curve. A refined evaluation procedure, taking into account saturation effects in the signals, reduces the uncertainty in our data to around 1%.

The measurement of high-dimensional entangled states of orbital angular momentum prepared by spontaneous parametric down-conversion can be considered in two separate stages: a generation stage and a detection stage. Given a certain number of generated modes, the number of measured modes is determined by the measurement apparatus. We derive a simple relationship between the generation and detection parameters and the number of measured entangled modes.

Cold hydrogen-hydrogen scattering has been investigated using close coupling approximation (CCA) model. The total wave function of the system is expanded in terms of atomic expansion basis. The effect of electron exchange and coupling to the continuum of both the atoms are taken into account. Singlet and triplet partial wave elastic and total cross-sections are presented and compared with existing theoretical predictions. Thermally averaged total cross-sections with respect to temperature are also provided along with their earlier results.