Presence Of Dissipative Processes Research Articles

Gate‐Based Protocol Simulations for Quantum Repeaters using Quantum‐Dot Molecules in Switchable Electric Fields

AbstractElectrically controllable quantum‐dot molecules (QDMs) are a promising platform for deterministic entanglement generation and, as such, a resource for quantum‐repeater networks. A microscopic open‐quantum‐systems approach based on a time‐dependent Bloch–Redfield equation is developed to model the generation of entangled spin states with high fidelity. The state preparation is a crucial step in a protocol for deterministic entangled‐photon‐pair generation that is proposed for quantum repeater applications. The theory takes into account the quantum‐dot molecules' electronic properties that are controlled by time‐dependent electric fields as well as dissipation due to electron–phonon interaction. The transition between adiabatic and non‐adiabatic regimes is quantified, which provides insights into the dynamics of adiabatic control of QDM charge states in the presence of dissipative processes. From this, the maximum speed of entangled‐state preparation is inferred under different experimental conditions, which serves as a first step toward simulation of attainable entangled photon‐pair generation rates. The developed formalism opens the possibility for device‐realistic descriptions of repeater protocol implementations.

Anomalous transverse resistance in the topological superconductor β-Bi2Pd

A supercurrent flowing in a superconductor meets no resistance. Yet an electric field may still be established within the superconductor in the presence of dissipative processes, such as vortex motion. Here we report the observation of a transverse voltage drop in superconducting β-Bi2Pd thin films. Unlike the Hall effect in general or in other superconductors, the sign of the observed transverse voltage does not depend on the external magnetic field. Instead, it is dictated by the broken inversion symmetry on the film interfaces. This anomalous transverse voltage, or transverse resistance, is indicative of a chirality that likely resonates with the topological surface states reported in β-Bi2Pd.

Tilted congruence with big rip singularity in f(T) theory of gravity

In this paper, tilted congruence with big rip singularity in f(T) theory of gravity is presented. f(T) theory of gravity is the generalization of the Teleparallel theory of gravity, where [Formula: see text] is the torsion scalar. In this work, tilted model is studied in which the three-velocity represents additional degree of freedom and tilted model detected the presence of dissipative processes including gravitational radiation. The solution of the field equations is explored by using the stiff fluid, power law of velocity field and a linear relationship between [Formula: see text] and [Formula: see text]. In this paper, the big bang and big rip singularity are observed. The cosmological evolution in f(T) model is examined. The physical and geometrical phases of the models are also investigated.

Power-Optimal Control of a Stirling Engine's Frictional Piston Motion.

The power output of Stirling engines can be optimized by several means. In this study, the focus is on potential performance improvements that can be achieved by optimizing the piston motion of an alpha-Stirling engine in the presence of dissipative processes, in particular mechanical friction. We use a low-effort endoreversible Stirling engine model, which allows for the incorporation of finite heat and mass transfer as well as the friction caused by the piston motion. Instead of performing a parameterization of the piston motion and optimizing these parameters, we here use an indirect iterative gradient method that is based on Pontryagin’s maximum principle. For the varying friction coefficient, the optimization results are compared to both, a harmonic piston motion and optimization results found in a previous study, where a parameterized piston motion had been used. Thus we show how much performance can be improved by using the more sophisticated and numerically more expensive iterative gradient method.

Optimized Piston Motion for an Alpha-Type Stirling Engine.

The Stirling engine is one of the most promising devices for the recovery of waste heat. Its power output can be optimized by several means, in particular by an optimized piston motion. Here, we investigate its potential performance improvements in the presence of dissipative processes. In order to ensure the possibility of a technical implementation and the simplicity of the optimization, we restrict the possible piston movements to a parametrized class of smooth piston motions. In this theoretical study the engine model is based on endoreversible thermodynamics, which allows us to incorporate non-equilibrium heat and mass transfer as well as the friction of the piston motion. The regenerator of the Stirling engine is modeled as ideal. An investigation of the impact of the individual loss mechanisms on the resulting optimized motion is carried out for a wide range of parameter values. We find that an optimization within our restricted piston motion class leads to a power gain of about 50% on average.

Molecular-dynamics approach for determining the vacancy heat of transport

We develop an approach for using equilibrium and nonequilibrium molecular-dynamics simulations to determine the heat of transport of a vacancy in a Lennard–Jones fcc crystal. The approach depends on computing the entropy and internal energy changes that accompany the hopping of a vacancy either parallel or antiparallel to a temperature gradient. We find that the internal energy, expressed in terms of the vacancy formation energy, is essentially unchanged during vacancy hops. However, we show that entropy is generated during vacancy hops, indicating the presence of dissipative processes. We show theoretically how the computation of the entropy generation is directly related to the reduced heat of transport. From an estimate of the enthalpy of vacancy formation, we determine the heat of transport, which is found to be positive in contradiction to previously-published results using a different method. The heat of transport we predict is quite close to the enthalpy of vacancy formation.

Internal friction method in studying elastic modulus defect of PdH x solution due to mobility of hydrogen atoms

The internal friction method in the free oscillation mode was used to study the temperature dependences of the dissipation loss spectra and shear modulus in a Pd polycrystalline system, PdH0.5 interstitial solid solution, and dehydrogenated Pd system. It is found in the studies of spectra and shear modulus that full hydrogen desorption from a- and b-phases of the PhH0.5 system occurs after the first heating cycle of the system. The dehydrogenated system, like the initial system, features the same number of peaks in the internal friction spectrum in the temperature range of 50–150×C. The temperature dependences of the shear modulus of the initial and dehydrogenated systems coincide. The presence of dissipative processes in the solid solution is related to mobility of hydrogen atoms in a FCC structure of Pd and causes a modulus defect in the temperature range of appearance of loss peaks in the spectrum. The possibility of describing the modulus defect within the phenomenological models in the inelasticity theory is considered.

Propagation of guided electron plasma waves on a plasma cylinder in the presence of dissipative processes

It is shown analytically that the presence of dissipative processes limits the propagation coefficient of guided electron plasma waves propagating along a plasma cylinder and that the main dipole and multiple resonances are limits of respective mode of guided electron plasma waves.

Propagation of guided electron plasma waves on a planar plasma slab in the presence of dissipative processes

The propagation of guided electron plasma waves on a planar plasma slab in the presence of dissipative processes has been investigated theoretically. It is shown that the presence of plasma or dielectric loss, limits the propagation coefficient β of these waves.