Electromagnetic States Research Articles

The effects of local density of states on surface plasmon polaritons

Surface plasmon polariton (SPP) is a kind of electromagnetic oscillation coupling due to the undulation of charge intensity, which is excited at the interface between metal and dielectric. With the help of near-field enhancement, surface plasmon polariton plays an important role in nano-photonics. When the effect of SPP is used to fabricate the single photon resource, not only the volume can be miniaturized, but also the single photon radiation and collection efficiency can be effectively improved. According to the relationship between the factor of Purcell effect and the density of states, we calculate the local density of electromagnetic states(LDOS) and Purcell factor. By analyzing the local densities of electromagnetic states of different metallic materials, we find that silver is the most suitable metal. For a certain metal, the detection distance and the dielectric material also have influences on local density of electromagnetic states and Purcell factor, and they provide important parameters for the designing of single photon resource based on surface plasmon resonances.

Multi-Hop Wireless Energy Transfer in WSNs

One major limitation in a Wireless Sensor Network (WSN) is the energy dissipation of the nodes and lifetime of the nodes battery. The aim of this paper is to overcome the power constraints in WSN by wirelessly charging the nodes using a newly discovered technique for single hop wireless energy transfer called Witricity. We investigate both theoretically and through simulations whether the physical phenomenon of long-lifetime resonant electromagnetic states with localized slowly-evanescent field patterns can be used to transfer energy efficiently over multiple hops.

Is there an instrumental drift in the counting rate of some high latitude neutron monitors?

For the last six decades the neutron monitors have provided a continuous string of very reliable data to the heliophysics community. Although neutron monitors are not the primary source of data for the galactic cosmic rays, these data serve as a baseline reference for the data collected by the detectors on board the satellites and deep space probes, far away from earth orbit. The pressure corrected hourly data are available from the World Data Centers. These data have been used to derive deep insights pertaining to the electromagnetic states of the heliosphere and the modes of transport of energetic charged particles in the tangled interplanetary magnetic fields. We present evidence that some of the high latitude neutron monitors are undergoing long-term drifts in their baselines. In particular, we argue that there is no physical basis to justify the observed long-term downward trend in the baseline of the South Pole neutron monitor. The real reason may have to do with its maintenance at a distant location with challenging logistics and an improper normalization of its data after the 26 months break in the 1970s.

Polarizations of coupling kinetic Alfvén and slow waves

Kinetic Alfvén waves (KAWs) are dispersive Alfvén waves with short perpendicular wavelengths and have been extensively applied to various energization phenomena of plasma particles. KAWs are coupled to slow magnetosonic waves in the case of a finite-β plasma. In this paper, the electromagnetic polarization states of the coupling KAWs and slow waves are investigated. The results show that the polarization states of these waves depend sensitively on the local plasma parameters such as the ion-electron temperature ratio (α=Ti/Te) and the plasma kinetic-magnetic pressure ratio (β=2μ0n(Ti+Te)/B2) as well as their perpendicular wavenumber (k⊥ρi). The polarization states of waves play an important and key role in wave-particle interactions and hence have a great interest of understanding the physics of particle energization phenomena by these waves.

Dirac-cone photonic surface states in three-dimensional photonic crystal slab

We present a multiple-scattering method in conjunction with supercell calculations to study the electromagnetic surface states in three-dimensional photonic crystal slab. Using our technique, we obtain the first prediction of Dirac-cone photonic surface state in some three-dimensional photonic crystal slabs. Such a state can be used to investigate some extremal transmission phenomena of electromagnetic waves near the Dirac point on the surface of the crystal, which is similar to the case of electron on the surface of topological insulators.

Optical properties of a metal nanosphere with spatially dispersive permittivity

To model elastic and inelastic light scattering on a metal nanosphere with spatially dispersive permittivity, an extension of the Lorenz–Mie theory is applied. The theory takes into account longitudinal vector spherical harmonics inside the sphere and determines the generalized Mie coefficients using a condition of vanishing electron flow through the sphere surface. In general, this condition is distinct from the conventional additional boundary condition of the continuity of the normal component of the electric field. Therefore, contrary to the common belief, the problem of divergence of the local density of electromagnetic states at the surface of an absorbing sphere is not solved by considering the spatial dispersion of the permittivity. We illustrate the theory by a study of the optical properties of a silver nanosphere using a hydrodynamic model for the dielectric function of the electron gas. Predictions of the nonlocal theory differ markedly from those of the local one if the sphere’s radius or the distance to the surface is smaller than a few nanometers. In particular, we demonstrate a shift of the Fröhlich resonance of nanometer-sized Ag particles caused by the spatial dispersion. Excitation of high-order spherical harmonics in larger particles is discussed. We show how the spatial dispersion decreases the rate of fluorescence quenching in close proximity to the particle surface.

Experimental Realization of Self-Guiding Unidirectional Electromagnetic Edge States

We present an experimental demonstration of self-guiding electromagnetic edge states existing along the zigzag edge of a honeycomb magnetic photonic crystal. These edge states are shown to possess unidirectional propagation characteristics that are robust against various types of defects and obstacles. In particular, they allow for the unidirectional transport of electromagnetic energy without requiring an ancillary cladding layer.

Control of near-field radiative heat transfer via surface phonon–polariton coupling in thin films

The possibility of controlling near-field radiative heat transfer with the use of silicon carbide thin films supporting surface phonon–polaritons in the infrared spectrum is explored. For this purpose, the local density of electromagnetic states is calculated and analyzed within the nanometric gap formed between two SiC films as well as the radiative heat flux exchanged between the thin layers.

Multistability at arbitrary low optical intensities in a metal-dielectric layered structure

We show that a nonlinear metal-dielectric layered slab of subwavelength thickness and very small average dielectric permittivity displays optical multistable behavior at arbitrary low optical intensities. This is due to the fact that, in the presence of the small linear permittivity, one of the multiple electromagnetic slab states exists no matter how small is the transmitted optical intensity. We prove that multiple states at ultra-low optical intensities can be reached only by simultaneously operating on the incident optical intensity and incidence angle. By performing full wave simulations, we prove that the predicted phenomenology is feasible and very robust.

Spin-orbit hybrid entanglement of photons and quantum contextuality

We demonstrate electromagnetic quantum states of single photons and of correlated photon pairs exhibiting "hybrid" entanglement between spin and orbital angular momentum. These states are obtained from entangled photon pairs emitted by spontaneous parametric down conversion, by employing a $q$-plate for coupling the spin and orbital degrees of freedom of a photon. Entanglement and contextual quantum behavior (that is also non-local, in the case of photon pairs) is demonstrated by the reported violation of the Clauser-Horne-Shimony-Holt inequality. In addition a classical analog of the hybrid spin-orbit photonic entanglement is reported and discussed.

Transmitting Hertzian Optical Nanoantenna with Free-Electron Feed

A pair of coupled gold nanorods excited by a beam of free electrons acts as a transmitting Hertzian antenna in the optical part of the spectrum. Significantly enhanced resonant emission is observed from the antenna when the electron beam is injected around the junction between the rods, where the local density of electromagnetic states is elevated.

Local density of electromagnetic states within a nanometric gap formed between two thin films supporting surface phonon polaritons

We present a detailed physical analysis of the near-field thermal radiation spectrum emitted by a silicon carbide (SiC) film when another nonemitting SiC layer is brought in close proximity. This is accomplished via the calculation of the local density of electromagnetic states (LDOS) within the gap formed between the two thin films. An analytical expression for the LDOS is derived, showing explicitly that (i) surface phonon polariton (SPhP) coupling between the layers leads to four resonant modes, and (ii) near-field thermal radiation emission is enhanced due to the presence of the nonemitting film. We study the impact of the interfilm separation gap, the distance where the fields are calculated, and the thickness of the nonemitting layer on the spectral distribution of the LDOS. Results show that for an interfilm gap of 10 nm, the near-field spectrum emitted around the SPhP resonance can increase more than an order of magnitude as compared to a single emitting thin layer. Interfilm SPhP coupling also induces a loss of spectral coherence of resonance, mostly affecting the low frequency modes. The effect of the nonemitting film can be observed on LDOS profiles when the distance where the fields are calculated is close to the interfilm gap. As the LDOS is calculated closer to the emitter, the near-field spectrum is dominated by SPhPs with small penetration depths that do not couple with the modes associated with the nonemitting film, such that thermal emission is similar to what is observed for a single emitting layer. Spectral distribution of LDOS is also significantly modified by varying the thickness of the nonemitting film relative to the thickness of the emitting layer, due to an increasing mismatch between the cross-coupled SPhP modes. The results presented here show clearly that the resonant modes of thermal emission by a polar crystal can be enhanced and tuned, between the transverse and longitudinal optical phonon frequencies, by simply varying the structure of the system. This analysis provides the physical grounds to tune near-field thermal radiation emission via multilayered structures, which can find application in nanoscale-gap thermophotovoltaic power generation.

Observation of unidirectional backscattering-immune topological electromagnetic states

One of the most striking phenomena in condensed-matter physics is the quantum Hall effect, which arises in two-dimensional electron systems subject to a large magnetic field applied perpendicular to the plane in which the electrons reside. In such circumstances, current is carried by electrons along the edges of the system, in so-called chiral edge states (CESs). These are states that, as a consequence of nontrivial topological properties of the bulk electronic band structure, have a unique directionality and are robust against scattering from disorder. Recently, it was theoretically predicted that electromagnetic analogues of such electronic edge states could be observed in photonic crystals, which are materials having refractive-index variations with a periodicity comparable to the wavelength of the light passing through them. Here we report the experimental realization and observation of such electromagnetic CESs in a magneto-optical photonic crystal fabricated in the microwave regime. We demonstrate that, like their electronic counterparts, electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; we find that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections. These modes may enable the production of new classes of electromagnetic device and experiments that would be impossible using conventional reciprocal photonic states alone. Furthermore, our experimental demonstration and study of photonic CESs provides strong support for the generalization and application of topological band theories to classical and bosonic systems, and may lead to the realization and observation of topological phenomena in a generally much more controlled and customizable fashion than is typically possible with electronic systems.

One-way electromagnetic Tamm states in magnetophotonic structures

We study surface Tamm states in magnetophotonic structures magnetized in the Cotton–Mouton (Voigt) geometry. We demonstrate that the periodicity violation due to the structure truncation together with the violation of the time reversal symmetry due to the presence of magneto-optical materials gives rise to nonreciprocality of the surface modes. Dispersion of forward and backward modes splits and becomes magnetization dependent. This results in the magnetization-induced transitions between bulk and surface modes and unidirectional propagation of surface waves.

Lifetime statistics in chaotic dielectric microresonators

We discuss the statistical properties of lifetimes of electromagnetic quasibound states in dielectric microresonators with fully chaotic ray dynamics. Using the example of a resonator of stadium geometry, we find that a recently proposed random-matrix model very well describes the lifetime statistics of long-lived resonances, provided that two effective parameters are appropriately renormalized. This renormalization is linked to the formation of short-lived resonances, a mechanism also known from the fractal Weyl law and the resonance-trapping phenomenon.

Squeezed state generation in photonic crystal microcavities

The feasibility of using a parametric down-conversion process to generate squeezed electromagnetic states in three dimensional photonic crystal microcavity structures is investigated for the first time. The spectrum of the squeezed light is theoretically calculated by using an open cavity quantum mechanical formalism. The cavity communicates with two main channels, which model vertical radiation losses and coupling into a single-mode waveguide respectively. The amount of squeezing is determined by the correlation functions relating the field quadratures of light coupled into the waveguide. All of the relevant model parameters are realistically estimated for structures made in Al0.3Ga0.7As, using finite-difference time-domain simulations. Squeezing up to approximately 30% below the shot noise level is predicted for 10 mW average power, 80 MHz repetition, 500 ps excitation pulses using in a [111] oriented wafer.

Plasmons in the presence of Tamm-Shockley states with Rashba splitting at noble metal surfaces

Au(111) or similar noble metal surfaces feature Tamm-Shockley surface states that are known to possess considerable spin-orbit splitting of the Rashba type of order $\ensuremath{\Delta}=0.1\text{ }\text{eV}$. When interacting with an electromagnetic field such states are expected to have resonances when the frequency of the field is near the energy of the spin-orbit splitting $\ensuremath{\Delta}$. They originate from the intersubband transitions between spin-split subbands and can be observed in the frequency dependence of the surface impedance. Plasmons in thin metal films are gapless and can be strongly affected by these spin resonances, acquiring significant modification of the spectrum when it intersects the $\ensuremath{\omega}=\ensuremath{\Delta}$ line. Finally, an interesting demonstration of the intersubband resonances can be achieved when metal films are coated with ionic dielectrics that have a frequency of longitudinal or transverse optical phonons above or below $\ensuremath{\Delta}$. The dielectric function between the two optical phonon frequencies is negative which forbids propagation of conventional plasmon polaritons. However, the presence of spin-orbit-split surface states allows plasmon polaritons to exist in this otherwise forbidden range of frequencies.

Limits of slow light in photonic crystals

While ideal photonic crystals would support modes with a vanishing group velocity, state-of-the-art structures have still only provided a slow down by roughly two orders of magnitude. We find that the induced density of states caused by lifetime broadening of the electromagnetic modes results in the group velocity acquiring a finite value above zero at the band-gap edges while attaining superluminal values within the band gap. Simple scalings of the minimum and maximum group velocities with the imaginary part of the dielectric function or, equivalently, the linewidth of the broadened states are presented. The results obtained are entirely general and may be applied to any effect which results in a broadening of the electromagnetic states, such as loss, disorder, and finite-size effects. This significantly limits the reduction in group velocity attainable via photonic crystals.

Toward a minimum branching fraction for dark matter annihilation into electromagnetic final states

Observational limits on the high-energy neutrino background have been used to place general constraints on dark matter that annihilates only into standard model particles. Dark matter particles that annihilate into neutrinos will also inevitably branch into electromagnetic final states through higher-order tree and loop diagrams that give rise to charged leptons, and these charged particles can transfer their energy into photons via synchrotron radiation or inverse Compton scattering. In the context of effective field theory, we calculate the loop-induced branching ratio to charged leptons and show that it is generally quite large, typically $\ensuremath{\gtrsim}1%$, when the scale of the dark matter mass exceeds the electroweak scale, ${M}_{W}$. For a branching fraction $\ensuremath{\gtrsim}3%$, the synchrotron radiation bounds on dark matter annihilation are currently stronger than the corresponding neutrino bounds in the interesting mass range from 100 GeV to 1 TeV. For dark matter masses below ${M}_{W}$, our work provides a plausible framework for the construction of a model for ``neutrinos-only'' dark matter annihilations.

Quasi-Hermitian Hamiltonians, minimum-uncertainty (MU) angular momentum states and interferometers

Minimum-uncertainty (MU) angular momentum states which are eigenstates of a nonunitary angular momentum displacement operator are found also to be eigenstates of a quasi-Hermitian Hamiltonian which has a certain metric with real eigenvalues. Various properties of these states are discussed. The relations between electromagnetic (EM) MU angular momentum states which have been proposed for improving the resolution in interferometers and the present theory are discussed.