2,002 research outputs found
PT-symmetric laser-absorber
In a recent work, Y.D. Chong et al. [Phys. Rev. Lett. {\bf 105}, 053901
(2010)] proposed the idea of a coherent perfect absorber (CPA) as the
time-reversed counterpart of a laser, in which a purely incoming radiation
pattern is completely absorbed by a lossy medium. The optical medium that
realizes CPA is obtained by reversing the gain with absorption, and thus it
generally differs from the lasing medium. Here it is shown that a laser with an
optical medium that satisfies the parity-time symmetry
condition for the dielectric
constant behaves simultaneously as a laser oscillator (i.e. it can emit
outgoing coherent waves) and as a CPA (i.e. it can fully absorb incoming
coherent waves with appropriate amplitudes and phases). Such a device can be
thus referred to as a -symmetric CPA-laser. The general
amplification/absorption features of the CPA-laser below lasing
threshold driven by two fields are determined.Comment: 5 pages; to be published in Phys. Rev. A (Rapid Communications
Dynamical oscillations in nonlinear optical media
The spatial dynamics of pulses in Kerr media with parabolic index profile are
examined. It is found that when diffraction and graded-index have opposite
signs propagating pulses exhibit an oscillatory pattern, similar to a breathing
behavior. Furthermore, if the pulse and the index profile are not aligned the
pulse oscillates around the index origin with frequency that depends on the
values of the diffraction and index of refraction. These oscillations are not
observed when diffraction and graded-index share the same sign
Anyonic symmetry, drifting potentials and non-Hermitian delocalization
We consider wave dynamics for a Schr\"odinger equation with a non-Hermitian
Hamiltonian satisfying the generalized (anyonic) parity-time
symmetry , where
and are the parity and time-reversal operators. For a stationary
potential, the anyonic phase just rotates the energy spectrum of
in complex plane, however for a drifting potential the energy
spectrum is deformed and the scattering and localization properties of the
potential show intriguing behaviors arising from the breakdown of the Galilean
invariance when . In particular, in the unbroken
phase the drift makes a scattering potential barrier reflectionless, whereas
for a potential well the number of bound states decreases as the drift velocity
increases because of a non-Hermitian delocalization transition.Comment: 7 pages, 5 figure
Accelerating Quantum Decay by Multiple Tunneling Barriers
A quantum particle constrained between two high potential barriers provides a paradigmatic example of a system sustaining quasi-bound (or resonance) states. When the system is prepared in one of such quasi-bound states, the wave function approximately maintains its shape but decays in time in a nearly exponential manner radiating into the surrounding space, the lifetime being of the order of the reciprocal of the width of the resonance peak in the transmission spectrum. Naively, one could think that adding more lateral barriers would preferentially slow down or prevent the quantum decay since tunneling is expected to become less probable and due to quantum backflow induced by multiple scattering processes. However, this is not always the case and in the early stage of the dynamics quantum decay can be accelerated (rather than decelerated) by additional lateral barriers, even when the barrier heights are arbitrarily large. The decay acceleration originates from resonant tunneling effects and is associated to large deviations from an exponential decay law. We discuss such a counterintuitive phenomenon by considering the hopping dynamics of a quantum particle on a tight-binding lattice with on-site potential barriers
In the beginning was the song: The complex multimodal timing of mother-infant musical interaction
In this commentary we raise three issues: (1) Is it motherese or song that sets the stage for very early mother-infant interaction? (2) Does the infant play a pivotal role in the complex temporal structure of social interaction? (3) Is the vocal channel primordial or do other modalities play an equally important role in social interaction
Design for Manufacturing of Electro-Mechanical Assemblies in the Aerospace Industry
Electronic design engineers struggle continuously to obtain a satisfactory trade-off between item performance and cost. On one hand, they would like to employ the best material and components available on the market and opt for time-consuming manufacturing processes in order to obtain high-performance parts. On the other hand, such choice would lead to high recurring cost making the part less attractive in the market. In this scenario, industrial engineering team becomes a crucial industrial entity. It assists the Design Engineers by providing design rules or guidelines. This guidance is intended to provide recommendation to the development team in order to define what is technically feasible and achievable inside an industrial process contest. These rules should not be too strict in order to guarantee acceptable part performance and therefore market attractiveness. The rules contain guidelines on mechanical, process and material aspects. This chapter will focus on design for manufacturing of electro-mechanical parts for the aerospace industry typically being a high-end and high-performance part. Nevertheless, cost and time remain a key aspect to guarantee. The effects of such rules on mechanical and electrical performance will be highlighted and discusses, with a specific focus ion high frequency electrical assemblies (1–30 GHz). It will also contain a review on microelectronic production techniques that impact on the part’s electrical performance
Optical realization of the two-site Bose-Hubbard model in waveguide lattices
A classical realization of the two-site Bose-Hubbard Hamiltonian, based on
light transport in engineered optical waveguide lattices, is theoretically
proposed. The optical lattice enables a direct visualization of the
Bose-Hubbard dynamics in Fock space.Comment: to be published, J Phys. B (Fast Track Communication
UWB Circuits and Sub-Systems for Aerospace, Defence and Security Applications
In order to maintain technological superiority over other systems, modern equipment for aerospace, defence and security (ADS) applications require advanced integrated circuits operating at microwave and millimetre wave frequencies. High integration is necessary to obtain low SWaP-C features thus enabling the installation of this category of equipment in unfriendly environments: compact spaces, and subject to heavy mechanical loads and temperature stress. This chapter reviews the topology, technology and trends of microwave circuits in UWB systems for ADS applications. Amplification at high frequency is a crucial function: high power amplifiers in the transmit (Tx) chain and low-noise amplifiers in the receive (Rx) chain will be revised, in addition to medium-power (gain) amps. Signal conditioning and routing is also essential: MIMO architecture are becoming the standard and therefore switching and signal phasing and attenuation is increasingly needed, to obtain the desired beam steering and shaping. Each type of circuits leverages the benefits of either gallium nitride (GaN) or gallium arsenide (GaAs), and the role of the semiconductor will be explained. Finally, an outline on multi-functional circuits (single-chip front-ends and core-chips) will be presented: the trend is to realize the whole microwave section of a Tx/Rx module with only to MMICs that perform all the functionalities requested at microwave frequencies
Zitterbewegung of optical pulses in nonlinear frequency conversion
Pulse walk-off in the process of sum frequency generation in a nonlinear
crystal is shown to be responsible for pulse jittering which is
reminiscent to the Zitterbewegung (trembling motion) of a relativistic freely
moving Dirac particle. An analytical expression for the pulse center of mass
trajectory is derived in the no-pump-depletion limit, and numerical examples of
Zitterbewegung are presented for sum frequency generation in periodically-poled
lithium niobate. The proposed quantum-optical analogy indicates that frequency
conversion in nonlinear optics could provide an experimentally accessible
simulator of the Dirac equation.Comment: to be published in Journal of Physics B: Atomic, Molecular & Optical
Physic
Spectral singularities and Bragg scattering in complex crystals
Spectral singularities that spoil the completeness of Bloch-Floquet states
may occur in non-Hermitian Hamiltonians with complex periodic potentials. Here
an equivalence is established between spectral singularities in complex
crystals and secularities that arise in Bragg diffraction patterns. Signatures
of spectral singularities in a scattering process with wave packets are
elucidated for a PT-symmetric complex crystal.Comment: 6 pages, 5 figures, to be published in Phys. Rev.
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