Electromagnetic Cavity Mode Research Articles

Dipole nano-laser

Theoretically predicted ‘‘dipole lasing’’, i.e., spontaneous excitation of coherent metal nano-particle dipole oscillations through interaction with a quantum-dot two-level system subject to population inversion is demonstrated. Equations for dipole lasing are the same as equations for ordinary laser, where the dipole momentum of nano-particle stands for the electromagnetic field cavity mode. Dipole lasing frequency corresponds to the localized plasmon resonance of the nano-particle. Dipole momentum of nano-particle leads to coherent dipole radiation. Optical cavity is not necessary, the size of the dipole laser can be smaller than the optical wavelength, i.e. it is dipole nano-laser. Threshold conditions and optical bistability in dipole nano-lasers are considered.

Nonlocal electrodynamics of long ultranarrow Josephson junctions: Experiment and theory

Abstract We experimentally and theoretically investigate electromagnetic cavity modes in ultra-narrow Al-AlOx-Al and Nb-AlOx-Nb long Josephson junctions. Experiments show that the voltage spacing between the Fiske steps on the current-voltage characteristics of sub-μm wide and several hundred μm long Al-AlOx-Al and Nb-AlOx-Nb Josephson junctions increases when decreasing the width of a junction. This effect is explained by stray magnetic fields, which become important for narrow junctions. Theoretical estimates of the Fiske step voltage based on a nonlocal wave propagation equation are in good agreement with our experimental data. Using the nonlocal model, we determine the size and mass of a Josephson vortex by means of a variational approach, and relate vortex size to the experimentally measured critical magnetic field of the junction.

Josephson vortex interaction mediated by cavity modes: Tunable coupling for superconducting qubits

A quantum-mechanical model for the interaction of Josephson vortices (fluxons) embedded in superconducting transmission line is presented. The vortices interact through emission and absorption of linear waves (electromagnetic cavity modes). We show that in a classical regime this peculiar type of interaction is determined by the product of instantaneous velocities of fluxons. In a quantum regime, this property provides tunable coupling between vortices which can be used for entanglement of vortex qubits. The physical mechanism of the vortex interaction is similar to that proposed for qubits based on trapped ions. Different types of transmission lines mediating the vortex interaction are proposed.

MICROTUBULES IN BIOLOGICAL CELLS AS CIRCULAR WAVEGUIDES AND RESONATORS

The microtubules in the cellular cytoskeleton have a fundamental role in the living processes of biological cells. They are hollow cylinders which resemble circular waveguides or cylindrical resonators. The cutoff and resonant frequencies of the transverse magnetic and transverse electric modes of the microtubule cavities are in the band of soft x-rays. This suggests the possibility of interaction of electromagnetic cavity modes with inner electrons in atoms (e.g., in carbon, nitrogen, and oxygen). Biological cells (e.g., the yeast cells of spherical shape) may also represent cavity resonators. In this case, the resonant frequencies may be in the infrared region.

Observation of Nonlinear Coupled Photon-Magnon Oscillations in YIG

Nonequilibrium spin waves excited by the parallel pumping in an yttrium iron garnet placed in a microwave cavity was studied by means of additional weak microwave signal. The response of the probe signal represented a two-hump spectrum just above the threshold of parametric instability. It corresponds to mixed oscillations of photons and magnons and demonstrates that the parametric spin-wave pair behaves as a single-mode oscillator nonlinearly coupled with the electromagnetic mode of microwave cavity. We observed another splitting in the spectrum before the onset of auto-oscillations. It is assumed to indicate that this steady state of parametric system consists of two different parametric spin-wave pairs. Theoretical calculations which consider coupled systems of resonator mode and magnetic sample are found to be in good agreement with the experimental data.

Investigation of stabilized resonant cavity microwave plasmas for propulsion

Results are presented for the performance of a microwave electrothermal thruster utilizing bluff-body and swirling flow stabilized plasmas with helium and nitrogen propellent. Stabilized plasmas have been produced in the TM011 electromagnetic cavity mode with coupling efficiencies approaching 100% and specific powers up to 27.3 MJ/kg. Fluid dynamic measurements indicate specific impulses of up to 543 s, efficiencies of 44-69%, and thrusts of 0.27—0.40 N with helium propellant. Spectroscopic results indicate plasma core electron temperatures of 11,840-12,170 K with extremely flat radial profiles. Nomenclature A = orifice area, m c = speed of light, m/s cp = specific heat, J/kg K g = gravitational acceleration, m/s2 7sp = specific impulse, s k = Boltzmann's constant, J/K m = particle mass, kg m = mass flow rate, kg/s P,- = incident power, W Po = chamber pressure, Pa Pr = reflected power, W R = gas constant, J/kg K 7} = thrust, N T(k, = stagnation temperature (cold), K Tl}l, = stagnation temperature (hot), K ue = exhaust velocity, m/s y = ratio of specific heats 77 = efficiency j]c = coupling efficiency A = wavelength, A

Application of the displaced oscillator basis in quantum optics.

Fock states and coherent states have been widely applied in analyses of quantum-optics experiments. In this paper, the application of a set of basis functions that consist of a product of displaced harmonic-oscillator states for the electromagnetic field and atomic states that are eigenfunctions of the momentum operator will be explored. For the case of a single mode, these states are the exact eigenfunctions in the limiting case where the electromagnetic-field mode frequency is much larger than the atomic transition frequency. This choice of basis functions will be used to analyze the interaction of a nonrelativistic, ``two-level'' atom with a single-frequency, quantized electromagnetic-field mode. Since in this basis the sign of the displacement of the electromagnetic-field state depends on the state of the atom, these new basis wave functions exhibit explicitly some aspects of atom-field correlations that are intrinsically quantum mechanical in nature. The analysis will be performed in the electric-dipole approximation for an atomic system that obeys the \ensuremath{\Delta}m=0 selection rule. The rotating-wave-approximation (RWA) terms cannot be made negligible through judicious choice of the field polarization for this system. The diamagnetic term, ${\mathit{e}}^{2}$${\mathbf{A}}^{2}$/2${\mathit{mc}}^{2}$, which is of the same order of magnitude as the RWA terms, is taken into account exactly by slightly modifying the traditional approach to quantizing the electromagnetic field. In this way the physical effects of the diamagnetic term are absorbed into a new electromagnetic cavity mode frequency.An approximate expression for the combined system's energy eigenvalues is found up to third order in the ratio of one-half the atomic transition frequency to the mode frequency. This expression indicates that inclusion of the RWA terms adds a small ``ripple'' on top of the smoothly varying energy eigenvalues when they are plotted as a function of the atom-field coupling constant. The ripple is interpreted as ``interference'' between two displaced oscillator-field states that represent the unperturbed state. When the Fock states are used as the basis for expanding the wave function of this system, a formidable five-term recurrence relation results. However, expanding the wave function in terms of the displaced harmonic-oscillator basis results in a less formidable three-term recurrence relation for the quantum coefficients.

Quantum Zeno effect induced by quantum-nondemolition measurement of photon number.

Measurements performed on a system will alter the dynamics of that system, and in the strong-measurement limit, can theoretically freeze the free evolution completely. This is the quantum Zeno effect. We utilize quantum-nondemolition photon-counting techniques to realize the Zeno effect on the evolution of either a two-level Jaynes-Cummings atom interacting with a resonant cavity mode, or on two electromagnetic modes configured as a multilevel parametric frequency converter. These systems interact with another electromagnetic cavity mode via a quadratic coupling system based on four-wave mixing and constructed so as to be a nondemolition measurement of the photon number. This mode is then coupled to the environment through the cavity mirrors. This measurement is shown to be a measurement of system populations, which generates the desired Zeno effect and in the strong-measurement limit will freeze the free dynamics of the system.

Dynamic Stark effect for the Jaynes-Cummings system.

We calculate the quasienergies and steady states of a coupled two-level atom and quantized electromagnetic cavity mode with the cavity mode driven by a periodic classical field. The atom, the cavity mode, and the classical field are all on resonance. The quasienergies give shifted Jaynes-Cummings level splittings. These splittings are reduced by the interaction with the driving field and vanish at a threshold value of the driving field strength. Above the threshold, discrete quasienergies and normalizable steady states do not exist. Below the threshold, for weak driving fields, the steady states are squeezed and displaced Jaynes-Cummings eigenstates. We discuss the relevance of these results to work in cavity quantum electrodynamics.

Incoherent excitation of the Jaynes-Cummings system

The authors calculate scattered, transmitted and reflected spectra for a coupled two-level atom and quantized electromagnetic cavity mode driven by broad-band chaotic light. They obtain analytical results in the secular approximation and compare these with exact numerical results. Under cavity QED conditions (strong dipole coupling) the spectra show multiple resonances at the incommensurate transition frequencies of the Jaynes-Cummings Hamiltonian. They obtain expressions for linewidths and transition amplitudes that help them to assess the prospects for an experimental observation of these Jaynes-Cummings resonances.

Interaction of a charged harmonic oscillator with a single quantized electromagnetic field mode.

The interaction of an atomic system with a single mode of a quantized electromagnetic field is investigated in the dipole approximation. Two approximations that are almost always made in this analysis are the neglect of the diamagnetic term in the Hamiltonian and the dropping of the rotating-wave approximation (RWA) terms that correspond to processes that do not conserve energy. Both approximations involve the neglect of terms that are of the same order of magnitude so that consistency demands that they be considered together. It is demonstrated that, in the dipole approximation, a minor modification of the usual application of quantum electrodynamics to any atomic system can exactly incorporate the effects of the diamagnetic term into a new frequency of the electromagnetic cavity mode; this frequency is slightly different from that of the empty cavity. This result is then applied to the specific case of a charged harmonic oscillator interacting with a single mode. For this simple model an analytic solution can then be found that includes the effects of the diamagnetic term and does not use the RWA. It is found that, for off resonance, the normal modes of the coupled system oscillate at shifted frequencies which are in agreement with the second-order perturbation-theory calculation of the Lamb shift. When the cavity mode is tuned to the atomic oscillator frequency, the perturbation-theory Lamb-shift calculation is no longer valid, and the exact solution derived in this paper predicts a resonant Lamb shift that is significantly larger than the off-resonant single-mode Lamb shift. Furthermore, the frequency spectrum is qualitatively changed from the single frequency of the free atomic system to a doublet spectrum. An analytic solution of this harmonic-oscillator problem can also be found when the RWA terms are dropped from the Hamiltonian. Comparison of the two solutions reveals that the RWA terms contribute a frequency shift of magnitude independent of the field intensity in the simple case of a charged harmonic oscillator.When trajectories of the exact and RWA solutions are compared in phase space, it is found that one effect of the RWA terms is to lift a twofold degeneracy of the phase-space orbits that occurs when the RWA terms are neglected. The harmonic-oscillator problem has several features in common with the interaction of a two-level atom with a single quantized field mode. Both Hamiltonians exhibit inversion symmetry and hence have parity as a good quantum number. Both Hamiltonians contain RWA terms. When these RWA terms are neglected, both Hamiltonians have a new constant of motion that can be identified with the total number of excitations in the combined system.

The effect of the time-dependent self-consistent electrostatic field on gyrotron operation

The time-dependent self-consistent electrostatic field is shown to have a deleterious effect on gyrotron operation. As the electron beam density increases, the nonlinear efficiency is degraded seriously by the self-electrostatic field. Time-dependent multimode simulations demonstrate that at sufficiently large beam densities the electron cyclotron instability is quenched and the oscillation will not start. Contrary to previous investigations, electrostatic effects do not necessarily increase the linear growth rate of the electromagnetic cavity mode and, depending on the beam density, electrostatic effects can actually stabilize the mode. Typically, however, considerations of linear theory are not important in an overmoded, open resonator gyrotron because the system evolves nonlinearly into a state consisting of a single mode which is linearly stable, but nonlinearly the most efficient mode.

Boundary Conditions and Spatial Variations Associated with the Dynamic Modes of Josephson Tunnel Junctions

The Dynamic modes of Josephson Tunnel junctions have been investigated by the scanning laser technique and numerical simulations. The results clearly demonstrate the existence of the vortex mode and electromagnetic cavity mode which have distinctly different dc current distributions. The appropriate boundary condition used for calculations to describe our junctions was found to have the bias current fed from the edges.

On Electromagnetic Environmental Fidelity in Damped Cylindrical Cavities

A study is made of the electromagnetic cavity mode structure of a cylindrical tank containing a cylindrical damper membrane. Maxwell's equations for the most general mode of a cylindrical tank is considered and reduced to the problem of solving a single transcendental equation written in terms of the Bessel function of the first and second kind. This equation is solved numerically for some representative damped cavities yielding modal frequencies and damping rates.

Model of Interacting Radiation and Matter. III. Multimode Gas Lasers

We extend the investigation of the long-time behavior of a model consisting of N two-level atoms interacting with a single electromagnetic cavity mode to include interaction with many cavity modes. We show that, as a consequence of the coupling between radiation modes produced by spatial density variations of the population inversion, there is no strictly stationary state possible for multimode behavior. However we obtain a stationary state by neglecting the rapidly oscillating terms. The steady-state population inversion is then a solution of an eigenvalue problem. The eigenvalue determinate is a function of the number of modes and the coupling between modes in addition to the usual dependence on frequencies and relaxation times. We explicitly solve for the unique eigenvalue in special cases. The corresponding eigenvector gives the steady-state mode intensity ratios. The absolute values of the steady-state intensities are determined by the energy conservation equation generalized to include pumping and dissipation. We also calculate the steady-state frequency shifts for each mode. The mode frequency shifts are practically independent of each other and have the same functional form as the single-mode frequency shifts.

Brownian Motion of a Quantum Oscillator

An action principle technique for the direct computation of expectation values is described and illustrated in detail by a special physical example, the effect on an oscillator of another physical system. This simple problem has the advantage of combining immediate physical applicability (e.g., resistive damping or maser amplification of a single electromagnetic cavity mode) with a significant idealization of the complex problems encountered in many-particle and relativistic field theory. Successive sections contain discussions of the oscillator subjected to external forces, the oscillator loosely coupled to the external system, an improved treatment of this problem and, finally, there is a brief account of a general formulation.

Theory of the Ferromagnetic Microwave Amplifier

The theory of ferromagnetic microwave amplification is presented in detail. All three possible types of operation using, respectively, two electromagnetic cavity modes, two sample modes, and one sample and one cavity mode, are discussed. One especially simple case, that of a sphere in the first type of operation is treated separately. Thereafter all three cases are discussed in terms of scaler and vector potentials. An appendix deals with the gain-band-width problem and gives an expression for the equivalent ``negative Q'' of the sample.