Vol 39, No 5 (2018)

In this work, we study an inverse dynamical problem for a bipartite quantum system governed by the time local master equation: to find the class of generators which give rise to a certain time evolution with the constraint of fixed reduced states (marginals). The compatibility of such choice with a global unitary evolution is considered. For the nonunitary case, we propose a systematic method to reconstruct examples of master equations and address them to different physical scenarios.

We describe a recently introduced single-step traveling-wave quantum state engineering scheme using the one-dimensional coherent-state representation introduced by Janszky. In this representation, the photon number expansion of the output state is derived in a compact formula that is advantageous for numerical optimization. Using this formula, we determine several sets of physically controllable parameters of the scheme yielding various nonclassical target states.

We investigate the dynamics of charge carriers propagating in a ring being induced by twisted light: The exciting laser beam is assumed to have nonzero orbital angular momentum. The selection rules for the transitions between the eigenstates of the two-dimensional ring are determined with the aid of analytic and numerical methods. Using these results, we gain an insight into the physical process that leads to the transfer of the angular momentum of the laser beam to the electrons in the quantum ring.

We propose a new concept of localized surface plasmon polariton (SPP) mode excitation in a spherical nanoparticle, which utilizes a collective mechanism of dissipative instability in an adjacent 2D plasma carrying a DC electric current. We show that 2D DC current becomes unstable at optical frequencies when the drift velocity exceeds the speed of sound in the 2D plasma. Dissipative instability emerges as a result of self-consistent 2D plasma oscillations coupled to the electromagnetic modes of the nanosphere, the material of which is absorbing at given frequency (i.e., the dielectric permittivity Imε > 0), and instability is absent in the case of transparent material. We derive the dispersion equation for this dissipative instability by a self-consistent solution of the Maxwell equations for the electromagnetic modes and the hydrodynamic equations for the 2D plasma current. Our estimates demonstrate attainment of very high instability increments Imω ~ 10¹⁵ s⁻¹, which makes the proposed concept very promising for excitation of plasmonic nanoantennas.

We present a short discussion of the results presented in the contributions to the Special issue consisting of two parts and dedicated to the memory of Professor Stig Stenholm and Professor Jozsef Janszky. Our goal here is to provide a connection of these results with general problems in foundations of quantum mechanics. We discuss the relation of the developments in better understanding the foundations of quantum mechanics to its intuitively difficult notion of states and observables in such important systems as laser photons, oscillations realized by molecular vibrations, currents in superconducting circuits based on Josephson junction devices, and trapped ions with efforts in scientific activities like scientific collaborations of Russian, European, USA, and other institutions and organization of long-living series meetings like Central European Workshops on Quantum Optics (CEWQO) and International Conferences on Squeezed States and Uncertainty Relations (ICSSUR) with publications in international Scientific Journals. We present some discussions of the works of researchers and their results in the area of fundamental theory.

We present a general and fascinating problem of quantum entanglement (QE) that is calculated with the help of quantum Fisher information (QFI) and von Neumann entropy (VNE) for moving two-level atomic systems. We calculate numerically the temporal evolution of the state vector of the entire system under the influence of intrinsic decoherence for a moving two-level atom. We demonstrate that the phase shifts of an estimator parameter, intrinsic decoherence, and the atomic motion play an important and prominent role during the time evolution of the atomic system. We observe that there is a monotonic relation between the atomic quantum Fisher information (QFI) and quantum entanglement (QE) in the absence of atomic motion. We also show that at the revival time the local maximum values of QFI decreases gradually. A periodic behavior of QFI is observed in the presence of atomic motion, which becomes more important and remarkable for two-level atomic systems. Moreover, the atomic quantum Fisher information and entanglement demonstrate an opposite response during the time evolution in the presence of atomic motion. We show that the evolution of entanglement is more susceptible to the intrinsic decoherence; a considerable change occurs in the degree of entanglement when the intrinsic decoherence parameter increases. Intrinsic decoherence in the atom–field interaction represses the nonclassical effects of the atomic systems. Both the entanglement and the quantum Fisher information saturate to their lower levels for longer time scales in the presence of intrinsic decoherence. For larger values of intrinsic decoherence, the sudden death of entanglement is observed.