45915 research outputs found
Sort by
Pseudo-Hermiticity and generalized PT- and CPT-symmetries
No full textWe study certain linear and antilinear symmetry generators and involution operators associated with pseudo-Hermitian Hamiltonians and show that the theory of pseudo-Hermitian operators provides a simple explanation for the recent results of Bender, Brody and Jones (quant-ph/0208076) on the CPT-symmetry of a class of PT-symmetric non-Hermitian Hamiltonians. We present a natural extension of these results to the class of diagonalizable pseudo-Hermitian Hamiltonians H with a discrete spectrum. In particular, we introduce generalized parity (P), time-reversal (T), and charge-conjugation (C) operators and establish the PT- and CPT-invariance of H
Full-wave modeling of "early" VLF perturbations caused by lightning electromagnetic pulses
No full textWe use the three-dimensional full-wave method and Born approximation technique to calculate the scattered VLF field in the near zone of ionospheric disturbances created by lightning electromagnetic pulses. The method fully accounts for the anisotropicity of the ionosphere magnetized by a nonvertical geomagnetic field. We calculate the VLF amplitude perturbation on the ground for vertical and horizontal lightning discharge configurations. The results show that the magnitude of the scattered signal is strongly dependent on the direction of the incident VLF wave
Semiconductor and dielectric microsphere based channel dropping filters and detectors
No full textDielectric and semiconductor microspheres coupled to optical fibers are used for optical channel dropping in the infrared communication wavelengths of 810 and 1300 nm. Additionally, a dielectric microsphere coupled to an optical fiber and placed in close proximity to a silicon photodiode is used for resonant detection of communication signals at 810 nm. The observed resonances have quality factors of 100.000. The measured quality factors are limited by the sensitivity of the measurement setup. These optical resonances provide the necessary narrow linewidths that are needed for high resolution optical communication applications. The microsphere, optical fiber, and detector system shows promise as a building block for optoelectronic integration
Interplay between Rashba spin-orbit coupling and adiabatic rotation in a two-dimensional Fermi gas
No full textWe explore the trap profiles of a two-dimensional atomic Fermi gas in the presence of a Rashba spin-orbit coupling and under an adiabatic rotation. We first consider a noninteracting gas and show that the competition between the effects of Rashba coupling on the local density of single-particle states and the Coriolis effects caused by rotation gives rise to a characteristic ring-shaped density profile that survives at experimentally accessible temperatures. Furthermore, Rashba splitting of the Landau levels gives the density profiles a ziggurat shape in the rapid-rotation limit. We then consider an interacting gas under the BCS mean-field approximation for local pairing, and study the pair-breaking mechanism that is induced by the Coriolis effects on superfluidity, where we calculate the critical rotation frequencies both for the onset of pair breaking and for the complete destruction of superfluidity in the system. In particular, by comparing the results of a fully-quantum-mechanical Bogoliubov-de Gennes approach with those of a semiclassical local-density approximation, we construct extensive phase diagrams for a wide range of parameter regimes in the trap where the aforementioned competition may, e.g., favor an outer normal edge that is completely phase separated from the central superfluid core by vacuum
Quantum coherence and correlations of optical radiation by atomic ensembles interacting with a two-level atom in a microwave cavity
No full textWe examine quantum statistics of optical photons emitted from atomic ensembles which are classically driven and simultaneously coupled to a two-level atom via microwave photon exchange. Quantum statistics and correlations are analyzed by calculating second-order coherence degree, von Neumann entropy, spin squeezing for multiparticle entanglement, as well as genuine two-and three-mode entanglement parameters for steady-state and nonequilibrium situations. Coherent transfer of population between the radiation modes and quantum-state mapping between the two-level atom and the optical modes are discussed. A potential experimental realization of the theoretical results in a superconducting coplanar waveguide resonator containing diamond crystals with nitrogen-vacancy color centers and a superconducting artificial two-level atom is discussed
Resonance phenomenon related to spectral singularities, complex barrier potential, and resonating waveguides
No full textA peculiar property of complex scattering potentials is the appearance of spectral singularities. These are energy eigenvalues for certain scattering states that similarly to resonance states have infinite reflection and transmission coefficients. This property reveals an interesting resonance effect with possible applications in waveguide physics. We study the spectral singularities of a complex barrier potential and explore their application in designing a waveguide that functions as a resonator. We show that for the easily accessible sizes of the waveguide and its gain region, we can realize the spectral singularity-related resonance phenomenon at almost every wavelength within the visible spectrum or outside it
Quantum correlated light pulses from sequential superradiance of a condensate
No full textWe discover an inherent mechanism for entanglement swap associated with sequential superradiance from an atomic Bose-Einstein condensate. Based on careful examinations with both analytical and numerical approaches, we conclude that as a result of the swap mechanism, Einstein-Podolsky-Rosen-type quantum correlations can be detected among the scattered light pulses
Semiclassical analysis of spectral singularities and their applications in optics
No full textMotivated by possible applications of spectral singularities in optics, we develop a semiclassical method of computing spectral singularities. We use this method to examine the spectral singularities of a planar slab gain medium whose gain coefficient varies due to the exponential decay of the intensity of the pumping beam inside the medium. For both singly and doublypumped samples, we obtain universal upper bounds on the decay constant beyond which no lasing occurs. Furthermore, we show that the dependence of the wavelength of the spectral singularities on the value of the decay constant is extremely mild. This is an indication of the stability of optical spectral singularities
Exact cosmological solution of the coupled Einstein-Majorana fermion-scalar field equations
No full textWe couple a neutral scalar field and a Majorana fermion field to Einstein gravity represented by the Robertson-Walker metric and find a class of exact cosmological solutions
Many-body effects on the melting and dynamics of small clusters
No full textUsing a potential recently proposed by Baskes [Phys. Rev. Lett. 83, 2592 (1999)], we study the influence of the many-body interactions on the thermodynamics and chaotic dynamics of small atomic clusters. With standard molecular dynamics simulations as well as parallel tempering Monte Carlo, we calculate the complete heat capacity curves and the variations of the largest Lyapunov exponent with total energy. We observe that increasing the magnitude or decreasing the range of the many-body forces leads to an increase of chaos and a decrease in the melting temperature. Decreasing the range of the many-body interactions also results in a significantly lower latent heat of melting