Phase Covariant Channel: Quantum Speed Limit of Evolution

The quantum speed of evolution for the phase covariant map is investigated. This involves absorption, emission, and dephasing processes. The maps under various combinations of the above processes are considered to investigate the effect of phase covariant maps on quantum speed limit time. For absorption-free phase covariant maps, combinations of dissipative and CP-(in)divisible (non)-Markovian dephasing noises are considered. The role of coherence-mixedness balance on the speed limit time is checked in the presence of both vacuum and finite temperature effects. The rate at which Holevo's information changes and the action quantum speed of evolution for specific cases of the phase covariant map are also investigated.     

Quantum Correlations and Speed Limit of Central Spin Systems

In this article, single, and two-qubit central spin systems interacting with spin baths are considered and their dynamical properties are discussed. The cases of interacting and non-interacting spin baths are considered and the quantum speed limit (QSL) time of evolution is investigated. The impact of the size of the spin bath on the quantum speed limit for a single qubit central spin model is analyzed. The quantum correlations for (non-)interacting two central spin qubits are estimated and their dynamical behavior with that of QSL time under various conditions are compared. How QSL time could be availed to analyze the dynamics of quantum correlations is shown.     

Quasiprobability distributions in open quantum systems: Spin-qubit systems

We study nonclassical features in a number of spin-qubit systems including single, two and three qubit states, as well as an N$N$ qubit Dicke model and a spin-1 system, of importance in the fields of quantum optics and information. This is done by analyzing the behavior of the well known Wigner, P$P$, and Q$Q$ quasiprobability distributions on them. We also discuss the not so well known F$F$ function and specify its relation to the Wigner function. Here we provide a comprehensive analysis of quasiprobability distributions for spin-qubit systems under general open system effects, including both pure dephasing as well as dissipation. This makes it relevant from the perspective of experimental implementation.     

Kinetics and Mechanism of the Oxidation of Propan-1-ol and Propan-2-ol by Permanganate in the Absence and Presence of Tween-20 in Perchloric Acid Medium

The kinetics of the oxidation of propan-1-ol and propan-2-ol by KMnO₄ in HClO₄ medium has been studied in absence and presence of Tween-20. In the absence of Tween-20 the reaction is of first order with respect to each of permanganate and H⁺, but of complex order with respect to substrate. The active oxidant species HMnO₄ reacts with the alkanol molecule to form an intermediate complex, which decomposes in the rate-determining step to form the respective product and Mn^v. In the presence of Tween-20, both the oxidant and the substrate are distributed between the aqueous phase and the micellar pseudo-phase and then react. Different kinetic and thermodynamic parameters have been evaluated. Compensation between water structure destruction and substrate–micelle interaction plays an important role in the presence of the surfactant.     

The two-qubit amplitude damping channel: Characterization using quantum stabilizer codes

A protocol based on quantum error correction based characterization of quantum dynamics (QECCD) is developed for quantum process tomography on a two-qubit system interacting dissipatively with a vacuum bath. The method uses a 5-qubit quantum error correcting code that corrects arbitrary errors on the first two qubits, and also saturates the quantum Hamming bound. The dissipative interaction with a vacuum bath allows for both correlated and independent noise on the two-qubit system. We study the dependence of the degree of the correlation of the noise on evolution time and inter-qubit separation.     

Event-based parareal: A data-flow based implementation of parareal

Parareal is an iterative algorithm that, in effect, achieves temporal decomposition for a time-dependent system of differential or partial differential equations. A solution is obtained in a shorter wall-clock time, but at the expense of increased compute cycles. The algorithm combines a fine solver that solves the system to acceptable accuracy with an approximate coarse solver. The critical task for the successful implementation of parareal on any system is the development of a coarse solver that leads to convergence in a small number of iterations compared to the number of time slices in the full time interval, and is, at the same time, much faster than the fine solver. Very fast coarse solvers may not lead to sufficiently rapid convergence, and slow coarse solvers may not lead to significant gains even if the number of iterations to convergence is satisfactory. We find that the difficulty of meeting these conflicting demands can be substantially eased by using a data-driven, event-based implementation of parareal. As a result, tasks for one iteration do not wait for the previous iteration to complete, but are started when the needed data are available. For given convergence properties, the event-based approach relaxes the speed requirements on the coarse solver by a factor of ～K, where K is the number of iterations required for a converged solution. This may, for many problems, lead to an efficient parareal implementation that would otherwise not be possible or would require substantial coarse solver development. In addition, the framework used for this implementation executes a task when the data dependencies are satisfied and computational resources are available. This leads to improved computational efficiency over previous approaches that pipeline or schedule groups of tasks to a particular processor or group of processors.     

Radiation from a Circular Waveguide Flush-mounted to a Ground Plane covered by a Plasma or a Dielectric Slab

A theory of the radiation from the open end of a circular waveguide fed in the dominant TE₁₁ mode and flush-mounted to an infinite, perfectly conducting flat ground plane covered by a plasma or a dielectric sheath is developed. In this analysis, the contributions to the aperture admittance and the excited fields from the higher order TE_1n (n ≥ 1) and TM_1l(l ≥ 1) modes are included. The aperture admittance for which the higher order modes are considered, has been calculated by two methods: 1. variational technique and 2. successive iteration method. It is shown that for any desired order of accuracy the results of these approaches are identical. Expressions for radiated fields, surface waves for all radial values of r, and the fields which represent glancing incident fields inside the slab are derived. The contribution of the surface waves to the aperture admittance is also presented.