Excitation Of Cavity Modes Research Articles

Entanglement distillation for atomic states via cavity QED

Following a recent proposal (Phys. Rev. Lett. 85 (2000) 2392) about quantum information processing using dispersive atom–cavity interaction, in this paper, we proposed a physical scheme to concentrate the pure non-maximally entangled atomic states via cavity QED by using atomic collision in a far-off-resonant cavity. The most distinctive advantage of our scheme is that there is no excitation of cavity mode during the distillation procedure. Therefore the requirement on the quality of cavity is greatly loosened.

Cavity Mode Excitation by Vortex Shedding from a Cross-Beam

An analysis is made of the tonal acoustic radiation produced by nominally steady, low Mach number flow past a shallow, rectangular wall cavity in the presence of a cross-beam in the flow adjacent to the cavity. At ‘lock-on’ the frequency of vortex shedding from the beam is equal to one of the resonant frequencies of the cavity. The sound produced by this vorticity is augmented by the presence of the cavity and is calculated for the lowest order resonance frequency of the cavity by using a Green's function derived by Howe ( International Journal of Aeroacoustics2, 347 – 365, 2003). Except for beams of very small cross-section, the efficiency of the aeroacoustic coupling between the beam and the cavity depends on the position of the beam above the cavity. Our results indicate that the coupling is strongest when the beam lies above the cavity mouth between the cavity leading edge and the centre of the mouth. The analysis makes use of two alternative models of vortex shedding, involving either an array of discrete, rectilinear vortices or a continuous, time-harmonic vortex sheet in the wake of the beam. At lock-on each of these models supplies essentially identical predictions of the acoustic sound power radiated directly away from the cavity.

A detector of high frequency gravitational waves based on coupled microwave cavities

Superconducting microwave cavities have been proposed for the detection of gravitational waves in the high frequency range of the spectrum. The interaction of the gravitational wave with the cavity walls, and the resulting motion, induces the transition of some electromagnetic energy from an initially excited cavity mode to an empty one. The energy transfer is maximum when the frequency of the wave is equal to the frequency difference of the two cavity modes. In this paper, some ideas for the development of a tunable detector of gravitational waves around 10 kHz are discussed; the outline of a possible detector design and its expected sensitivity are also shown.

Multiple paths to enhance optical transmission through a single subwavelength slit.

In this Letter, we explore transmission properties of a single subwavelength slit flanked by a finite array of grooves made on a thick metallic film. We identify three main mechanisms that can enhance optical transmission: groove cavity mode excitation (controlled by the depth of the grooves), in-phase groove reemission (controlled by the period of the groove array), and slit waveguide mode (controlled by the thickness of the metal film). By tuning these geometrical parameters, enhancements of transmission of light by up to 2 orders of magnitude can be achieved when all three mechanisms coincide. Experimental verification of these findings is also shown for structured silver films fabricated by focused-ion-beam milling.

Considerations on parametric instability in Fabry–Perot interferometer

We evaluate the parametric phenomenon for the main optical mode coupled to other resonant waves excited by acoustic interaction with the mirrors of a Fabry–Perot. We apply this to the arm cavity of a gravitational wave antenna. Under certain assumptions we find that the amplitude of these parasitic modes is expressed by analytic solutions that are always damped. We analyze both the zero detuning and the detuned case and solve the equations. The form of the solution shows that for equally spaced and excited cavity modes the instability is expressed by a threshold condition, which is well approximated for LIGO arm resonator parameters.

Optimization of the mode matching in pulsed cavity ringdown spectroscopy by monitoring non-degenerate transverse mode beating

A simple and reliable method is presented for optimizing the mode matching of a laser beam to the high-finesse cavity used in pulsed cavity ringdown spectroscopy (CRDS). The method is based on minimizing the excitation of higher-order transverse cavity modes through monitoring the non-degenerate transverse mode beating which becomes visible with induced cavity asymmetry caused by slight misalignment. No additional instrument is required other than a pinhole aperture, thus this method can be applied for CRDS experiments in the whole wavelength range. Measurements of the CRDS absorption spectrum of acetylene (C2H2) near 571 nm demonstrate that the mode-matching optimization improves the sensitivity of pulsed CRDS.

Field-dipole orientation mechanism and higher order modes in atom guides

In cavity quantum electrodynamics (CQED), cavity size, dipole position and dipole orientation are the main factors controlling cavity effects, for example, suppression and enhancement of spontaneous emission. However, the dynamical effects of dipole orientation in CQED have, to date, remained largely unexplored, with most treatments simply concentrating on two (or three) orthogonal directions to illustrate the variations of CQED effects with dipole orientation. No mechanism which determines the evolution of the dipole orientation has been put forward to describe typical situations where atoms move in the field of an excited cavity mode. We emphasize here that in the presence of a cavity mode, the average dipole orientation is automatically determined at every point to be parallel to the direction of the electric field vector of the cavity mode. Besides giving rise to a single value for the spontaneous emission rate, this mechanism is shown to have important consequences for the dynamics of atoms in atom guides. In particular, it determines the average trapping potential distributions and the average radiation forces which guide the atoms along a cylindrical cavity. The effects of the field-dipole orientation mechanism are illustrated with reference to typical situations involving sodium atoms in sub-micron cylindrical guides. The role of a higher order cavity mode of the cylinder in the dynamics is highlighted in terms of its influence on the rotational and vibrational motions in such guides.

Single-atom laser based on multiphoton resonances at far-off resonance in the Jaynes-Cummings ladder

We propose a scheme of a one-atom laser which produces a cavity-field virtually in a stationary Fock state. It is based upon the unexpectedly simple dynamics of the Jaynes-Cummings system at multiphoton resonances at far-off resonance. We find that an anomalously high cavity mode excitation occurs at a particular set of atomic, cavity, and driving-field frequencies.

Linear and nonlinear excitations in two stacks of parallel arrays of long Josephson junctions

We investigate a structure consisting of two parallel arrays of long Josephson junctions sharing a common electrode that allows inductive coupling between the arrays. A model for this structure is derived starting from the description of its continuous limit. The excitation of linear cavity modes known from continuous and discrete systems as well as the excitation of a new state exhibiting synchronization in two dimensions are inferred from the mathematical model of the system. The stable nonlinear solution of the coupled sine-Gordon equations describing the system is found to consist of a fluxon-antifluxon string. This is a two-dimensional phase-locked solitonic mode. Both linear and nonlinear excitations are numerically investigated and experimentally demonstrated in two stacks of five-junction arrays.

Kelvin-Helmholtz driven modes of the magnetosphere

Ultralow frequency (ULF) waves in the magnetosphere are thought to be driven by disturbances of the magnetopause caused by the flow in the magnetosheath. In this paper a model showing how the trapping and excitation of these modes depends upon the shear flow and propagation angle is presented. The ideal magnetohydrodynamics (MHD) equations are used and the perturbations are assumed to be linear. A bounded, uniform magnetospheric cavity, with a finite plasma beta, separated by a vortex sheet from a semi-infinite, field-free, flowing magnetosheath is considered. It is shown that the bounded model allows the trapping and excitation of both fast and slow cavity modes, and that unstable surface modes may also exist. Slow surface modes are unstable only for a small interval of flow speed, becoming fast surface modes for higher flows. Slow cavity modes have small growth rates and are unlikely to be significant observationally. It is shown that fast modes propagating quasiparallel to the flow may be excited for realistic flow speeds, but that for nonparallel modes, much higher flows are required. Finally, an exact method for predicting the onset of instability for fast modes is derived and is shown to occur at the coalescence of modes of opposite energy.

Atom dynamics between conducting plates

The dynamics of atoms subject to laser light propagating between perfectly conducting parallel plates is investigated. In the semiclassical approximation the motion of atoms in this context is governed by a van der Waals--type potential, together with a dynamic dipole potential that comes into play as soon as a cavity mode is excited. In addition, the atoms become subject to an average dissipative (spontaneous) force associated with the cavity mode that always acts parallel to the plates. We show that, by a suitable choice of field intensity and detuning, the total transverse potential can be used to confine atoms in transverse vibrational states, while their motion in the parallel direction is controlled by the dissipative force. Significant variations of the characteristics of the system with atom velocity, dipole orientation, and type of excited cavity mode are emphasized. These features are illustrated using typical parameters for the case of sodium atoms between parallel plates with subwavelength separations.

The effects of external optical feedback on the power penalty of DFB-LD modules for 2.5Gbs−1 optical transmission systems

We report the effects of external optical feedback on the power penalty of commercial distributed feedback laser diode (DFB-LD) modules for 2.5Gbs−1 optical transmission systems. External optical feedback presented to the DFB-LD modules causes the excitation of external cavity modes, resulting in increased relative intensity noise (RIN) and intensity noise ripples at low frequency region below 500MHz. For a 10−10 bit error rate (BER), the minimum power penalty is as much as 1.25dB for a feedback ratio of −8.8dB. An excess power penalty of 0.5dB per 3dB increase in the feedback ratio was also empirically obtained. We suggest that optical isolators in 2.5Gbs−1 DFB-LD modules used in conventional optical transmission systems or WDM systems must have a peak isolation ratio of better than 54.5dB, instead of the previously recommended 30dB, for negligible power penalty induced by external optical feedback.

Imaging of electromagnetic resonances in a YBa2Cu3O7- delta bicrystal grain-boundary Josephson junction.

We report on spatially resolved measurements of dynamic states of a high-critical-temperature superconductor Josephson junction. The experiments were performed with a ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thin-film grain-boundary Josephson junction fabricated on an yttria-stabilized zirconia bicrystal substrate. We identified the excitation of one-dimensional self-resonant cavity modes (Fiske resonances) with a spatial resolution of about 1--3 \ensuremath{\mu}m using low-temperature scanning electron microscopy. Our imaging results with this Josephson junction are in fair agreement with results obtained with high-quality Nb/${\mathrm{AlO}}_{\mathit{x}}$/Nb tunnel junctions having a uniform dielectric tunnel barrier.

SUSAN (Superconducting Systems Analysis) by Low Temperature Scanning Electron Microscopy (LTSEM)

Low-temperature scanning electron microscopy was used for spatially resolved investigations of both Josephson junctions and superconducting integrated circuits during their operation with a spatial resolution of about 1 mu m. Using single Josephson tunnel junctions of various geometries, the authors studied different dynamic states such as fluxon oscillations or unidirectional flux flow. With an integrated circuit consisting of a two-dimensional array of tunnel junctions and an RF detection circuit they investigated the RF properties of the coupling circuit and confirmed the existence of an impedance mismatch and a geometrical standing wave in the blocking capacitor. The studies of the dynamics of single Josephson tunnel junctions of various geometries showed a linear behavior (excitation of single cavity modes) if the boundary conditions dominate, and otherwise a nonlinear behavior (excitation of solutions).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Excitation and amplification of cavity oscillations in spherically converging shells.

The stability of thin shells under arbitrary radial motions can be described by the evolution of two independent surface modes for the inside and outside shell boundaries. The evolution equations can be consistently decoupled for all mode numbers, and specific solutions for ballistic and accelerated shell motions are discussed. They show strong dependences on initial conditions and can explain significant amplification for low mode numbers by interference effects. The theory is applied to the excitation of cavity modes in accelerated high-aspect-ratio shells. By comparison with numerical solutions for the full shell equations, the validity of the analytic predictions is confirmed and the saturated oscillation amplitudes after acceleration can be estimated. The further amplification of these modes by convergence and deceleration effects is discussed and potential inertial confinement fusion applications are illustrated by a simple implosion model.

Spectral characteristics of hydromagnetic waves in the magnetosphere

This work is intended to explain why the resonant response of the magnetosphere prefers to have discrete frequencies. Using a cylindrical model for the outer magnetosphere with a plasma density profile proportional to 1/r, we show that the eigenequation characterizing the eigenmodes of the hydromagnetic waves in this model has two turning points along the radial axis. The locations of the turning points depend upon the values of the eigenperiod and the associated east-west wavenumber of the eigenmode. The energy spectrum of the excited cavity modes is seen to have sharp peaks at discrete frequencies when the surface perturbations have a uniform spectrum in the frequency range of interest. We, therefore, have also shown that only the discrete set of the magnetospheric cavity eigenmodes can efficiently couple the perturbations excited on the boundary of the magnetosphere to the field-line resonant mode excited inside the inner turning point of the cavity eigenmode. The most likely values of east-west wavenumbers and wave period range are determined.

Fiske steps in Josephson junctions

A theoretical study of the Fiske steps in superconductor-insulator-superconductor tunnel junctions has been carried out. When the amplitude of the excited cavity mode is small, our result reduces to that obtained by Eck et al. and Kulik. However, when the excitation amplitude is large, we found current-voltage characteristics qualitatively different from those previously obtained by Kulik. Furthermore, the maximum current-step height calculated was $0.38{I}_{0}(T)$, slightly larger than $0.34{I}_{0}(T)$ previously obtained by Kulik. We have also obtained the details of the dependences of the current-voltage characteristics on the applied magnetic field and the damping factor of the cavity mode in the junction.

Simultaneous excitation of low-frequency cavity modes in short Josephson tunnel junctions

We have studied the simultaneous excitation of the two lowest-frequency cavity modes in a Josephson tunnel junction free from an external magnetic field. Specifically, we have calculated the dc tunneling current contributed by the excitation of these modes when the junction is biased at a voltage $V=nh\frac{{\ensuremath{\nu}}_{c}}{(2e)}$ with $n=1 \mathrm{and} 2$ and ${\ensuremath{\nu}}_{c}$ being the fundamental frequency of the cavity mode. In general, the dc tunneling current depends upon the decay rates of the modes. For $V=2h\frac{{\ensuremath{\nu}}_{c}}{(2e)}$, we found that it can be as large as 0.55 ${I}_{0}(T)$. Here ${I}_{0}(T)$ is the temperature-dependent zero-voltage Josephson critical current of the junction. Furthermore, if the decay rates for the cavity modes are small, multiple solutions for the junction current exist, which implies a fine structure in the current voltage characteristics. For $V=h\frac{{\ensuremath{\nu}}_{c}}{(2e)}$ the dc tunneling current contributed by the cavity modes is zero as long as no magnetic field is applied.

Experiments with the CERN superconducting 500 MHz cavity

We report on a series of experiments with a superconducting 500 MHz single cell cavity of “spherical” shape fabricated from niobium sheet material. Design, fabrication and different room temperature surface treatments of cavity including ion bombardment cleaning are discussed. An experimental test set up was used which includes diagnostic systems such as: temperature mapping of the outside cavity wall in subcooled helium, scanning solid state X-ray detector close to the cavity wall, light detection from the cavities inside, probes to measure internal free electron currents and a spectrum analyser to detect the electron induced excitations of higher order cavity modes. The following general characteristics of the cavity were observed: At 4.2 K an accelerating field of 3 MV/m can be achieved safely with low losses ( Q=2 × 10 9; P diss=8.4 W/m). The residual rf losses are concentrated in the high electric field region the cavity surface and cannot be attributed to normal conducting metallic impurities but show dielectric loss proporties. Resonant electron loading (multipacting) was never observed. At field levels exceeding 3 MV/m non-resonant electron currents start to load the cavity Q and give rise to the excitation of higher order cavity modes. The electron sources are point like and located in the high electric field region of the cavity. The field emission nature and the location of the electron sources are determined by temperature mapping and X-ray diagnostic measurements and analyzed by computer simulation of electron trajectories. In the region between 4 and 5 MV/m the cavity field is limited by thermal instabilities (quenching) originating from point like loss regions predominantly found at the bottom part of the cavity. Some of these defects were observed to be created during high field operations of the cavity in several instances.

Cavity-mode excitation in a Josephson tunnel junction

Using Takanaka's theory of the zero-field dc-current steps of a Josephson tunnel junction, we have studied the effect of the junction $Q$ factor on the shape of the current step near the first even-order resonant voltage $V=h\frac{{\ensuremath{\nu}}_{c}}{e}$, where ${\ensuremath{\nu}}_{c}$ is the frequency of the fundamental cavity mode. In addition, we have found that the effect of a magnetic field on the step height can be qualitatively explained by modifying Takanaka's theory to include a magnetic-field-dependent term.