Electrodynamic System Research Articles

Dressed-state scheme for a fast CNOT gate

A dressed-state scheme, which aims to speed up the adiabatic population transfer, is applied for constructing a fast controlled-not (CNOT) gate in a cavity quantum electrodynamics system. Numerical simulations indicate that the average fidelity for constructing the CNOT gate is quite high and the gate operation time is relatively short. Moreover, the effects of the atomic spontaneous emissions and the photon leakages from the system on the average fidelity are discussed and the results show the scheme is robust against decoherence.

Vehicle Electromagnets Energy Supply of A.C. Combined Levitation and Traction System

Introduction. The combined levitation and traction system (CLTS) with alternating current represents a kind of electrodynamic suspension system in which the traction and levitation force are created by one set of onboard electromagnets, and the lifting force is provided at any speeds of the crew, including the zero speed. The disadvantages of the system are the low energy factor and the complexity of controlling the start-brake regimes. The scope of such a system can be passenger transportation within large cities and urban agglomerations for distances up to 100 km with speeds up to 150-200 km / h. Goal. The aim of the work is the solution of the complex problem of providing CLTS onboard electromagnets with electric power with an increased energy factor and the ability to control all driving regimes. Method (methodology). Mathematical modeling of electromagnetic and electromechanical processes with subsequent evaluation of technical and economic parameters of the CLTS were used. Results. A practically realizable version of the power supply system for the on-board electromagnets CLTS is proposed. Practical significance. The proposed version of the power supply system has significant advantages over previously considered ones: the ability to flexibly control all modes of CLTS traffic with an increased energy factor. Conclusion. The system of power supply of the CLTS with alternating current from the traction network of constant voltage 3 ... 5 kV with placement of autonomous inverters onboard the crew allows to reduce the mass of the on-board electrical equipment by 10-20%, to minimize the consumption of inactive power and to flexibly control all modes of the crew's movement.

Quantum Zeno and anti-Zeno effects in open quantum systems

Traditional approach on quantum Zeno effect (QZE) and quantum anti-Zeno effect (QAZE) in open quantum systems (implicitly) assumes the bath (environment) state returning to its original state after each instantaneous projective measurement on the system and thus ignores the cross-correlations of the bath operators between different Zeno intervals. However, this assumption is not generally true, especially for a bath with a considerably non-negligible memory effect and for a system repeatedly projected into an initial general superposition state. We find that in stark contrast to the result of a constant value found in the traditional approach, the scaled average decay rate in unit Zeno interval of the survival probability is generally time-dependent or has an oscillatory behavior. In the case of strong bath correlation, the transition between the QZE and QAZE depends sensitively on the number of measurements $N$. For a fixed $N$, a QZE region predicted by the tradition approach may be in fact already in the QAZE region. We illustrate our findings using an exactly solvable open qubit system model with a Lorentzian bath spectral density, which is directly related to realistic circuit cavity quantum electrodynamics systems. Thus the results and dynamics presented here can be verified by current superconducting circuit technology.

Speeding up adiabatic passage by adding Lyapunov control

We propose a scheme to speed up adiabatic passage by using Lyapunov control theory. This is a good choice to solve the problem that may emerge in Berry's transitionless quantum driving [M. V. Berry, J. Phys. A 42, 365303 (2009)]. That is, the extra couplings in the counterdiabatic driving Hamiltonian can be avoided by choosing the available control Hamiltonian in an actual physical system. As examples, we shorten the evolution time of adiabatic population transfer in a three-level system and the entanglement generation in a cavity quantum electrodynamics system. Moreover, the occupation of an intermediate state can be sharply suppressed by properly choosing the control Hamiltonian in the three-level system. The scheme can also be generalized to a complex system where the exact expressions of adiabatic eigenstates are difficult to obtain.

An application of ionic liquid for preparation of homogeneous collagen and alginate hydrogels for skin dressing

Ionic liquid due to its green nature as well as having the ability to dissolve biopolymer, was used in the preparation of collagen and alginate hydrogels. The collagen and alginate hydrogels were prepared in different ratios of collagen and alginate, labeled CA5040, CA6030 and CA7020. The prepared hydrogels were characterized with Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), Thermogravimetric analysis (TGA) analysis. The samples were evaluated for water uptake behavior and mechanical properties using electrodynamic fatigue testing system. The biocompatibility was assessed through hemolysis and MTT assay on rat mesenchymal stem cells (rMSC) which showed satisfactory results. The drug loading and subsequent antibacterial properties were also performed. The prepared collagen and alginate hydrogels are suggested to be used for skin dressing.

Shortcut to adiabatic passage in a three-level system via a chosen path and its application in a complicated system.

We construct a shortcut to an adiabatic passage in a three-level system by choosing a dressed state acting as an evolutive path. Two designed auxiliary pulses are added into the original pulses to eliminate the couplings between the chosen evolutive-path state and the other two dressed states. The same target state as one gotten by adiabatic passage can be rapidly obtained, and the population of the lossy intermediate state can be controlled by setting proper parameters. Furthermore, as an example, we use this method in the adiabatic-passage scheme [Opt. Express20, 014547 (2012)], a complicated cavity quantum electrodynamics system, to successfully accelerate the generation of the three-dimensional entanglement between a single atom and a Bose-Einstein condensate.

Control of optical bistability in the nonlinear regime of two-sided cavity quantum electrodynamics

We investigate the optical bistability behavior of a two-sided cavity quantum electrodynamics system. The non-linear input - output relation of the atom - cavity system coupled by two input light fields from two ends of the cavity can be controlled by a control light from the free space. Different from the common optical bistability phenomenon in the atom - cavity system, two separate bistability regions are observed. The bistability threshold and hysteresis loop can be well controlled by the control light. Because of field interference, the output light intensity becomes different with varying the relative phase of two incident fields. The output field intensity at the threshold of the first bistability region approaches zero with either increasing the detuning or lowering the intensity of the control light; thus, the perfect photon absorption condition is extended and a broadband near-perfect photon absorber is realized. Furthermore, we show an asymmetrical transmission feature due to field interference. (C) 2017 Optical Society of America

Asymptotic stability of a satellite with electrodynamic attitude control in the orbital frame

A satellite in a circular near-Earth orbit is under consideration. The three-axis stabilization of the satellite in the orbital coordinate system with the use of electrodynamic attitude control system is studied. No constraints are imposed on the Earth's magnetic field approximation. The gravity gradient disturbing torque acting on the satellite attitude dynamics is taken into account as the largest disturbing torque. With the use of the Lyapunov direct method, conditions under which electrodynamic control solves the problem are obtained. The restrictions on the control parameter values for which one can guarantee the asymptotic stability of the programmed satellite motion are found and represented in an explicit form. Comparison of the results of numerical simulation and analytical investigation demonstrate effectiveness of the proposed approach.

Quick calculation of Luneberg lens scattering signature

The paper focuses on solving the problem of diffraction of a linear polarization electromagnetic wave on multilayer bodies of a spherical shape, i.e. a metal sphere with a dielectric cover and Luneberg lens. For this purpose tensor Green function method was used. Within the research we described the electrodynamic system verifying the expressions obtained for the calculation of electromagnetic fields. Furthermore, we compared the obtained results of calculations with the results of simulation of a similar problem in the software package ANSYS HFSS . Finally, we estimated the computational burden and computing time for solving the problem in two ways

Surface Impedance Boundary Conditions applied to solving nonlinear electrodynamic systems

AbstractThe paper presents a method for solving electromagnetic field problems by applying impedance boundary conditions for systems including conducting bodies of nonlinear magnetic properties in an excited harmonic field. Three types of impedance boundary conditions were derived. A procedure for computing surface impedance based on the transfer matrix is proposed. This procedure has been tested by comparing computational results to calculations where time function distortions were considered, and to the experimental data.

VEHICLE ELECTROMAGNETS ENERGY SUPPLY OF A.C. COMBINED LEVITATION AND TRACTION SYSTEM

Introduction. The combined levitation and traction system (CLTS) with alternating current represents a kind of electrodynamic suspension system in which the traction and levitation force are created by one set of onboard electromagnets, and the lifting force is provided at any speeds of the crew, including the zero speed. The disadvantages of the system are the low energy factor and the complexity of controlling the start-brake regimes. The scope of such a system can be passenger transportation within large cities and urban agglomerations for distances up to 100 km with speeds up to 150-200 km / h. Goal. The aim of the work is the solution of the complex problem of providing CLTS onboard electromagnets with electric power with an increased energy factor and the ability to control all driving regimes. Method (methodology). Mathematical modeling of electromagnetic and electromechanical processes with subsequent evaluation of technical and economic parameters of the CLTS were used. Results. A practically realizable version of the power supply system for the on-board electromagnets CLTS is proposed. Practical significance. The proposed version of the power supply system has significant advantages over previously considered ones: the ability to flexibly control all modes of CLTS traffic with an increased energy factor. Conclusion. The system of power supply of the CLTS with alternating current from the traction network of constant voltage 3 ... 5 kV with placement of autonomous inverters onboard the crew allows to reduce the mass of the on-board electrical equipment by 10-20%, to minimize the consumption of inactive power and to flexibly control all modes of the crew's movement.

Relativistic twistron based on backward-wave oscillator with modulating reflector and an efficiency of 56%

Using numerical simulation, the operating mode of a relativistic Cherenkov microwave generator of the twistronic type has been demonstrated. The generator includes an electrodynamic system based on a backward-wave oscillator and modulating reflector with nonmonotonous, highly nonuniform energy exchange along the length of the system. The efficiency of power conversion from the electron beam to electromagnetic radiation is 56%, and the electronic efficiency is 66%. For an accelerating voltage of 340 kV and an electron beam current of 3.3 kA, the simulated generation power is 630 MW at a frequency of 9.7 GHz and a guiding magnetic field of 2.2 T.

Relativistic phase effect in modeling interactions between ultraintense laser beams and electrons plasma

In a series of previous papers we proved an accurate connection between quantum and classical equations in the case of electrodynamic systems. We have used this connection to elaborate simplified models for systems composed of very intense laser beams and electrons or atoms. These models are in good agreement with numerous experimental data from literature. In this paper we develop the above approach for the new field of interactions between ultraintense laser beams, having intensities in the range 1018 − 1022 W/cm2, and electron plasmas. We show that in this case new effects take place, such as the fact that the variation of the phase of the field at the point where the electron is situated, decreases when the intensity of the field increases, due to a strong relativistic behavior. This effect leads to an aperiodic behavior of the radiations generated by above interactions, and to a possible new method for solitary waves generation.

Characteristic spectra of circuit quantum electrodynamics systems from the ultrastrong- to the deep-strong-coupling regime

We report on spectra of circuit-quantum-electrodynamics (QED) systems in an intermediate regime that lies between the ultrastrong and deep-strong-coupling regimes, which have been reported previously in the literature. Our experimental results, along with numerical simulations, demonstrate that as the coupling strength increases, the spectrum of a circuit-QED system undergoes multiple qualitative transformations, such that several coupling regimes are identified, each with its own unique spectral features. The different spectral transformations can be related to crossings between energy level differences and to changes in the symmetries of the energy eigenstates. These results allow us to use qualitative spectral features to infer certain properties and parameters of the system.

Scaling, scattering, and blackbody radiation in classical physics

Here we discuss blackbody radiation within the context of classical theory. We note that nonrelativistic classical mechanics and relativistic classical electrodynamics have contrasting scaling symmetries which influence the scattering of radiation. Also, nonrelativistic mechanical systems can be accurately combined with relativistic electromagnetic radiation only provided the nonrelativistic mechanical systems are the low-velocity limits of fully relativistic systems. Application of the no-interaction theorem for relativistic systems limits the scattering mechanical systems for thermal radiation to relativistic classical electrodynamic systems, which involve the Coulomb potential. Whereas the naive use of nonrelativistic scatterers or nonrelativistic classical statistical mechanics leads to the Rayleigh–Jeans spectrum, the use of fully relativistic scatterers leads to the Planck spectrum for blackbody radiation within classical physics.

Application of Modified Bragg Structures in High-Power Submillimeter Cyclotron Autoresonance Masers

We perform theoretical analysis and numerical simulation of cyclotron autoresonance masers, in which we propose using electrodynamic systems in the form of hybrid two-mirror cavities based on modified and conventional Bragg reflectors. It is shown that a stable regime of narrow-band generation with a multimegawatt power level can be achieved at a frequency of about 300 GHz in the described scheme of a generator based on a near-axis, moderately relativistic electron beam with an accelerating voltage of 500 kV and a current of 10 A, where the transverse size (diameter) of the interaction space is about 5 wavelengths and the guiding magnetic field is about 5 T.

Coupled modes locally interacting with qubits: Critical assessment of the rotating-wave approximation

The interaction of qubits with quantized modes of electromagnetic fields has been largely addressed in the quantum optics literature under the rotating wave approximation (RWA), where rapid oscillating terms in the qubit-mode interaction picture Hamiltonian can be neglected. At the same time, it is generally accepted that provided the interaction is sufficiently strong or for long times, the RWA tends to describe physical phenomena incorrectly. In this work, we extend the investigation of the validity of the RWA to a more involved setup where two qubit-mode subsystems are brought to interaction through their harmonic coordinates. Our treatment is all analytic thanks to a sequence of carefully chosen unitary transformations which allows us to diagonlize the Hamiltonian within and without the RWA. By also considering qubit dephasing, we find that the purity of the two-qubit state presents non-Markovian features which become more pronounced as the coupling between the modes gets stronger and the RWA loses its validity. In the same regime, there occurs fast generation of entanglement between the qubits which is also not correctly described under the RWA. The setup and results presented here clearly show the limitations of the RWA in a scenario amenable to exact description and free from numerical uncertainties. Consequently, it may be of interest for the community working with cavity or circuit quantum electrodynamic systems in the strong coupling regime.

Mode Modification of Plasmonic Gap Resonances Induced by Strong Coupling with Molecular Excitons

Plasmonic cavities can be used to control the atom-photon coupling process at the nanoscale, since they provide an ultrahigh density of optical states in an exceptionally small mode volume. Here we demonstrate strong coupling between molecular excitons and plasmonic resonances (so-called plexcitonic coupling) in a film-coupled nanocube cavity, which can induce profound and significant spectral and spatial modifications to the plasmonic gap modes. Within the spectral span of a single gap mode in the nanocube-film cavity with a 3 nm wide gap, the introduction of narrow-band J-aggregate dye molecules not only enables an anticrossing behavior in the spectral response but also splits the single spatial mode into two distinct modes that are easily identified by their far-field scattering profiles. Simulation results confirm the experimental findings, and the sensitivity of the plexcitonic coupling is explored using digital control of the gap spacing. Our work opens up a new perspective to study the strong coupling process, greatly extending the functionality of nanophotonic systems, with the potential to be applied in cavity quantum electrodynamic systems.

Coherent Coupling of Remote Spin Ensembles via a Cavity Bus.

We report coherent coupling between two macroscopically separated nitrogen-vacancy electron spin ensembles in a cavity quantum electrodynamics system. The coherent interaction between the distant ensembles is directly detected in the cavity transmission spectrum by observing bright and dark collective multiensemble states and an increase of the coupling strength to the cavity mode. Additionally, in the dispersive limit we show transverse ensemble-ensemble coupling via virtual photons.

Ultrafast quantum computation in ultrastrongly coupled circuit QED systems

The latest technological progress of achieving the ultrastrong-coupling regime in circuit quantum electrodynamics (QED) systems has greatly promoted the developments of quantum physics, where novel quantum optics phenomena and potential computational benefits have been predicted. Here, we propose a scheme to accelerate the nontrivial two-qubit phase gate in a circuit QED system, where superconducting flux qubits are ultrastrongly coupled to a transmission line resonator (TLR), and two more TLRs are coupled to the ultrastrongly-coupled system for assistant. The nontrivial unconventional geometric phase gate between the two flux qubits is achieved based on close-loop displacements of the three-mode intracavity fields. Moreover, as there are three resonators contributing to the phase accumulation, the requirement of the coupling strength to realize the two-qubit gate can be reduced. Further reduction in the coupling strength to achieve a specific controlled-phase gate can be realized by adding more auxiliary resonators to the ultrastrongly-coupled system through superconducting quantum interference devices. We also present a study of our scheme with realistic parameters considering imperfect controls and noisy environment. Our scheme possesses the merits of ultrafastness and noise-tolerance due to the advantages of geometric phases.