Electromagnetic Field In Cavity Research Articles

Folded chaotic whispering-gallery modes in nonconvex, waveguide-coupled planar optical microresonators

Chaotic whispering-gallery modes have significance both for optical applications and for our understanding of the interplay between wave phenomena and the classical ray limit in the presence of chaotic dynamics and openness. In strongly non-convex geometries, a theorem by Mather rules out the existence of invariant curves in phase space corresponding to rays circulating in whispering-gallery patterns, so that no corresponding modes of this type are expected. Here we discuss numerical computations of the electromagnetic fields in planar dielectric cavities that are strongly non-convex becausethey are coupled to waveguides. We find a family of special states which retains many features of the chaotic whispering-gallery modes known from convex shapes: an intensity pattern corresponding to near-grazing incidence along extended parts of the boundary, and comparatively high cavity Q factors. The modes are folded into a figure-eight pattern, so overlap with the boundary is reduced in the region of self-intersection. The modes combine the phenomenology of chaotic whispering-gallery modes with an important technological advantage: the ability to directly attach waveguides without spoiling the Q factor of the folded mode. Using both a boundary-integral method and the FDTD technique, we explore the dependence of the phenomenon on wavelength in relation to cavity size, refractive-index contrast to the surrounding medium, and the degree of shape deformation. A novel feature that distinguishes folded from regular whispering gallery modes is that a given shape will support high-Q folded chaotic whispering gallery modes only in certain wavelength windows.

Frequency-Dependence Characterization of Electromagnetic Reverberation in Indoor Scenarios Based on 1–40 GHz Channel Measurements

A novel model for the reverberation time is proposed in this letter, based on room electromagnetics theory. While the commonly used models consider absorption based on a constant rate of wall interactions within a given time, the proposed model takes the variance of interactions into account. Moreover, the frequency dependence of electromagnetic reverberation characteristics in indoor environments is experimentally investigated from 1 to 40 GHz. The reverberation time is found to be a decreasing function of frequency. A model is then developed to predict the room's quality factor, reverberation time, and average absorption coefficient. Good agreement is obtained with the limited results reported in the literature for similar scenarios. This approach aims to be an accurate alternative to the reverberation time measurements and computations in indoor environments by linking it to the theory of electromagnetic fields in cavities.

Dynamics of a quantum oscillator coupled with a three-level Λ-type emitter

We investigate the quantum dynamics of a quantum oscillator coupled with the most upper state of a three-level $\Lambda-$ type system. The two transitions of the three-level emitter, possessing orthogonal dipole moments, are coherently pumped with a single or two electromagnetic field sources, respectively. We have found ranges for flexible lasing or cooling phenomena referring to the quantum oscillator's degrees of freedom. This is due to asymmetrical decay rates and quantum interference effects leading to population transfer among the relevant dressed states of the emitter's subsystem with which the quantum oscillator is coupled. As an appropriate system can be considered a nanomechanical resonator coupled with the most excited state of the three-level emitter fixed on it. Alternatively, if the upper state of the $\Lambda-$type system possesses a permanent dipole then it can couple with a cavity electromagnetic field mode which can be in the terahertz domain, for instance. In the latter case, we demonstrate an effective electromagnetic field source of terahertz photons.

Theory for cavity cooling of levitated nanoparticles via coherent scattering: Master equation approach

We develop a theory for cavity cooling of the center-of-mass motion of a levitated nanoparticle through coherent scattering into an optical cavity. We analytically determine the full coupled Hamiltonian for the nanoparticle, cavity, and free electromagnetic field. By tracing out the latter, we obtain a Master Equation for the cavity and the center of mass motion, where the decoherence rates ascribed to recoil heating, gas pressure, and trap displacement noise are calculated explicitly. Then, we benchmark our model by reproducing published experimental results for three-dimensional cooling. Finally, we use our model to demonstrate the possibility of ground-state cooling along each of the three motional axes. Our work illustrates the potential of cavity-assisted coherent scattering to reach the quantum regime of levitated nanomechanics.

Quantum Phase Properties in Collective Three-Level V-Type System with Diamagnetic Term

In this paper, we present a rigorous investigation of the quantum phase transitions (QPTs) for a model which describes the degenerate collective regime of a three-level V-configuration atoms Bose-Einstein condensate (BEC). We consider that the three-level atoms of a BEC coupled to an optical resonator (cavity) with high finesse in the presence of a diamagnetic term, i. e., a system of N-identical three-level atoms interacting with a one-mode quantized electromagnetic cavity field. Also, the different components of this system are labeled by the different phase factors. By using the Glauber’s coherent states for the field, we calculate the free energy and study the finite-temperature phase transition for this model in the thermodynamic limit (N → ∞). Also, the potential energy surfaces constructed by taking the expectation value with respect to the direct product for a test state a direct product of coherent Heisenberg-Weyl HW(1)-states (for the electromagnetic field ), and U(3) (for the atomic field, i. e., matter contribution) coherent states. Moreover, the scaled ground-state energy is obtained by taking the expectation value of an effective Hamiltonian in the framework of the mean-field approach. In the thermodynamic limit, the energy surface takes a simple form for a direct description of the phase transitions. The relation between the QPTs and the symmetry physics are established and the QPTs for this model are investigated numerically. The properties of both stability and the equilibrium are calculated using the catastrophe theory. We notice that the second-order phase transitions (superradiant (SR)) with multi-level systems might be achievable in a wide range of physical systems, especially those where it is possible to engineer the spec-tra and oscillator strengths.

Design and comparison of superconducting rf gun cavities and beam dynamics for linear electron accelerators

Abstract Designs and simulations of 1.4, 1.5, 1.6, and 1.8-cell SRF gun cavities are studied at a linear accelerator gun system and they are compared with each other. We obtain high power beam from high energy electron beam produced at a photocathode with high quantum efficiency, high average current laser with high brightness, and high accelerating gradient. Beam energy of the whole accelerator system is effected mainly by the optimized RF power usage inside cells, the RF power interaction with particle beams , and the accelerated beam obtained by using SRF-gun cells. Thus, the optimized beam parameters, the RF parameters, and the accelerator gun cavity parameters that depend on each cavity geometries of SRF gun are obtained and presented in this paper. Additionally, the energy values of the electrons with optimized emittance at the gun exit are achieved and shown. We will conclude our paper by giving the gun output energies specifying which elliptical cavity-cell geometry is more appropriate to push the beam further in consistent conditions. For the cavity electromagnetic fields and the geometric designs of the cavities and the solenoid, we have utilized 2D Superfish/Poisson and 3D Computer Simulation Technology Programs. Also beam dynamics studies are included for only 1.6-cell SRF gun cavity which has the highest quality factor in order to figure out how the beam behaves along the beamline at the gun system. Transverse emittance ( π mm mrad) and beam energy ( ∼ 3.5 MeV) at the exit of the gun system are obtained as expected.

Supersolid-Based Gravimeter in a Ring Cavity.

We propose a novel type of composite light-matter interferometer based on a supersolidlike phase of a driven Bose-Einstein condensate coupled to a pair of degenerate counterpropagating electromagnetic modes of an optical ring cavity. The supersolidlike condensate under the influence of the gravity drags the cavity optical potential with itself, thereby changing the relative phase of the two cavity electromagnetic fields. Monitoring the phase evolution of the cavity output fields thus allows for a nondestructive measurement of the gravitational acceleration. We show that the sensitivity of the proposed gravimeter exhibits Heisenberg-like scaling with respect to the atom number. As the relative phase of the cavity fields is insensitive to photon losses, the gravimeter is robust against these deleterious effects. For state-of-the-art experimental parameters, the relative sensitivity Δg/g of such a gravimeter could be of the order of 10^{-10}-10^{-8} for a condensate of a half a million atoms and interrogation time of the order of a few seconds.

Squeezed Vacuum Used to Accelerate the Search for a Weak Classical Signal

Many experiments that interrogate fundamental theories require detectors whose sensitivities are limited by the laws of quantum mechanics. In cavity-based searches for axionic dark matter, vacuum fluctuations in the two quadratures of the cavity electromagnetic field limit the sensitivity to an axion-induced field. In an apparatus designed to partially mimic existing axion detectors, we demonstrate experimentally that such quantum limits can be overcome through the use of squeezed states. By preparing a microwave cavity in a squeezed state and measuring just the squeezed quadrature, we enhance the spectral scan rate by a factor of $2.12 \pm 0.08$. This enhancement is in excellent quantitative agreement with a theoretical model accounting for both imperfect squeezing and measurement.

Perturbation theory to model shielding effectiveness of cavities loaded with electromagnetic dampeners

It is well-known that a slotted resonant cavity with high-quality factor exhibits interior electromagnetic (EM) fields that may be even larger than the external field. The authors aim to reduce the cavity's EM fields and quality factor over a frequency band analytically, numerically, and experimentally by introducing microwave absorbing materials in the cavity. A perturbation model approach was developed to estimate the quality factor of loaded cavities, which is validated against full-wave simulations and experiments. Results with 78.7 mils (2 mm) thick ECCOSORB-MCS absorber placed on the inside cavity wall above and below the aperture slot (with only 0.026% cavity volume) result in a reduction of shielding effectiveness >19 dB and reductions in quality factor >91%, providing confirmation of the efficacy of this approach.

Cavity quantum-electrodynamical polaritonically enhanced electron-phonon coupling and its influence on superconductivity.

So far, laser control of solids has been mainly discussed in the context of strong classical nonlinear light-matter coupling in a pump-probe framework. Here, we propose a quantum-electrodynamical setting to address the coupling of a low-dimensional quantum material to quantized electromagnetic fields in quantum cavities. Using a protoypical model system describing FeSe/SrTiO3 with electron-phonon long-range forward scattering, we study how the formation of phonon polaritons at the two-dimensional interface of the material modifies effective couplings and superconducting properties in a Migdal-Eliashberg simulation. We find that through highly polarizable dipolar phonons, large cavity-enhanced electron-phonon couplings are possible, but superconductivity is not enhanced for the forward-scattering pairing mechanism due to the interplay between coupling enhancement and mode softening. Our results demonstrate that quantum cavities enable the engineering of fundamental couplings in solids, paving the way for unprecedented control of material properties.

Entanglement of two dipole-coupled qubits induced by a detuned thermal field

In this paper we have investigated the dynamics of entanglement of two identical qubits non-resonantly interacting with one mode of a vacuum or a thermal electromagnetic field in lossless cavity in the presence of a direct dipole-dipole interaction. Based on the exact solution to the equation used in this analysis, the Peres-Horodecki entanglement parameter (negativity) for qubits has been found. Numerical simulation of the negativity for various model parameters has been carried out. It has been shown that the interactions of qubits with a thermal field in a cavity can lead to their entanglement. It has been established that the detuning and dipole-dipole interaction of qubits can be used to manipulate and control the amount of atomic entanglement.

Normal-mode splitting induced by homogeneous electromagnetic fields in cavities filled with effective zero-index metamaterials

In cavity quantum electrodynamics (cQED), how an atom behaves in a cavity is what people care about. The coupling strength (g) between cavity field and atoms plays a fundamental role in various QED effects including Rabi splitting. In the solid-state case, when an atomic-like two-level system such as a single quantum dot (QD) is placed into a cavity, Rabi splitting would occur if g is strong enough. In the classical limit, when a QD in a cavity changes into a classical oscillator, the normal-mode splitting would also take place. It is known that g relies on the local fields at the places of the QDs or classical oscillators inside the cavity. However, for both cases, the traditional cavity modes involved are all in the form of standing waves and the localized fields are position-dependent. To ensure strong coupling between QDs or classical oscillators and photons, they should be placed right at the place where the cavity field is maximum, which is very challenging. How is the positional uncertainty overcome? Recently, the peculiar behaviors of electromagnetic (EM) fields inside zero-index metamaterial (ZIM) in which permittivity and/or permeability are zero have aroused considerable interest. In ZIMs the propagating phase everywhere is the same and the effective wavelength is infinite, which strongly changes the scattering and mode properties of the EM waves. In addition to the above characteristics, the fields in ZIM could be homogeneous as required by Maxwell equations. While the special properties of ZIMs are investigated, the fabrication of ZIMs is widely studied. It is found that a two dimensional (2D) photonic crystal consisting of a square lattice of dielectric rods with accidental degeneracy can behave as a loss-free ZIM at Dirac point. To overcome the positional uncertainty, in this paper we propose a cavity filled with effective zero-index metamaterial (ZIM). When the ZIM is embedded in a cavity, the enhanced homogeneous fields can occur under the resonance condition. Finally, experimental verification in microwave regime is conducted. In the experiments, we utilize a composite right/left-handed transmission line with deep subwavelength unit cell to mimic a ZIM and use a metallic split ring resonator (SRR) as a magnetic resonator whose resonance frequency is determined by structural parameters. The experimental results that in general agree well with the simulations demonstrate nearly position-independent normal-mode splitting.

A moving three-level Λ-type atom in a dissipative cavity

In this paper, we consider a three-level Λ-type atom interacting with a two-mode of electromagnetic cavity field surrounded by a nonlinear Kerr-like medium, the atom and the field are suffering decay rates (i.e. the cavity is not ideal) when the multi-photon processes is considered. Also, the atom and the field are assumed to be coupled with a modulated time-dependent coupling parameter under the rotating wave approximation. The wave function and the probability amplitudes are obtained, when the atom initially prepared in the superposition states and the field initially in the coherent states, by solving the time-dependent Schrodinger equation by taking a proper approximation to the system of differential equations. An analytical expression of the atomic reduced density operator is given. We studied the degree of entanglement, between the field and atom, measure (DEM) via the concurrence, Shannon information entropy, momentum increment and diffusion, and finally we investigated the effects of decay rates and the time-dependent parameters on Husimi Q-function.

Dynamic evolution of double $$\Lambda $$ Λ five-level atom interacting with one-mode electromagnetic cavity field

In this paper, the model describing a double $$\Lambda $$ five-level atom interacting with a single mode electromagnetic cavity field in the (off) non-resonate case is studied. We obtained the constants of motion for the considered model. Also, the state vector of the wave function is given by using the Schrodinger equation when the atom is initially prepared in its excited state. The dynamical evolutions for the collapse revivals, the antibunching of photons and the field squeezing phenomena are investigated when the field is considered in a coherent state. The influence of detuning parameters on these phenomena is investigated. We noticed that the atom–field properties are influenced by changing the detuning parameters. The investigation of these aspects by numerical simulations is carried out using the Quantum Toolbox in Python (QuTip).

High Frequency Electromagnetic Scarring in Three-Dimensional Axisymmetric Concave Cavities

ABSTRACTThis article examines the localization of high frequency electromagnetic fields in three-dimensional axisymmetric cavities along periodic paths between opposing sides of the cavity. When these orbits lead to unstable localized modes they are known as scars. This article treats the case where the opposing sides, or mirrors, are concave, leading to interior foci. Particular attention is focused on the normalization through the electromagnetic energy theorem. Both projections of the field along the scarred orbit, as well as field point statistics, are examined. Statistical comparisons are made with a numerical calculation of the scars run with an axisymmetric simulation.

Evolution of an electromagnetic field in the presence of a mobile membrane

We consider a one-dimensional cavity composed of two perfect, fixed mirrors and a mobile membrane in between. Assuming that the membrane starts to move from rest and that the membrane moves appreciably in a time-scale much larger than the time-scale in which the cavity electromagnetic field evolves appreciably, we derive simple analytic formulas that describe to good approximation the evolution of the field and that provide an intuitive physical picture. These formulas take into account the position, velocity, and acceleration of the membrane and are valid for arbitrarily large displacements of the membrane along the cavity axis. Also, we deduce the conditions under which the field can be described to good approximation by a single instantaneous mode.

Position dependent optical coupling between single quantum dots and photonic crystal nanocavities

We demonstrate precise and quick detection of the positions of quantum dots (QDs) embedded in two-dimensional photonic crystal nanocavities. We apply this technique to investigate the QD position dependence of the optical coupling between the QD and the nanocavity. We use a scanning electron microscope (SEM) operating at a low acceleration voltage to detect surface bumps induced by the QDs buried underneath. This enables QD detection with a sub-10 nm precision. We then experimentally measure the vacuum Rabi spectra to extract the optical coupling strengths (gs) between single QDs and cavities, and compare them to the values estimated by a combination of the SEM-measured QD positions and electromagnetic cavity field simulations. We found a highly linear relationship between the local cavity field intensities and the QD-cavity gs, suggesting the validity of the point dipole approximation used in the estimation of the gs. The estimation using SEM has a small standard deviation of ±6.2%, which potentially enables the high accuracy prediction of g prior to optical measurements. Our technique will play a key role for deeply understanding the interaction between QDs and photonic nanostructures and for advancing QD-based cavity quantum electrodynamics.

A moving three-level atom interacting with a two-mode field: some atom–field aspects

In this paper, the interaction of a moving three-level atom and a two-mode quantized electromagnetic cavity field is extended to involve the effects of the atomic motion. Detuning parameters, Kerr nonlinearity, Stark shift contributions and arbitrary forms of intensity-dependent atom–field coupling have been taken into account. The constants of motion and the wave function, when the atom is initially prepared in superposition states and the field is initially prepared in squeezed coherent states, have been obtained. We calculate some statistical aspects such as atomic inversion, purity, Mandel Q-parameter, cross-correlation, momentum increment, momentum diffusion and Husimi Q-function.

High-Frequency Electromagnetic Scarring in Three-Dimensional Axisymmetric Convex Cavities

ABSTRACTThis article examines the localization of high-frequency electromagnetic fields in three-dimensional axisymmetric cavities along periodic paths between opposing sides of the cavity. When these orbits lead to unstable localized modes, they are known as scars. This article treats the case where the opposing sides, or mirrors, are convex. Particular attention is focused on the normalization through the electromagnetic energy theorem. Both projections of the field along the scarred orbit as well as field point statistics are examined. Statistical comparisons are made with a numerical calculation of the scars run with an axisymmetric simulation.

DYNAMICS OF TWO-LEVEL ATOMS INTERACTING WITH THERMAL FIELD FOR ENTANGLED INITIAL ATOMIC STATES

In this paper the entanglement dynamics for system of two two-level atoms interacting with a mode of thermal electromagnetic field in lossless cavity has been investigated. Initial atomic states are the entangled Bell type states. Using the full set of eigenvectors of the Hamiltonian of the considered model we have derived the exact solution for the density matrix for the whole system. On its basis the reduced atomic density matrix and Peres - Horodetcki parameter have been calculated. Calculating of entanglement parameter shows the possibility of high degree of entanglement even for large intensity of thermal field. Thus there is a possibility of maintenance and control over the degree of entanglement.