32,305 research outputs found
Spontaneous emission control in high-extraction efficiency plasmonic crystals
We experimentally and theoretically investigate exciton-field coupling for
the surface plasmon polariton (SPP) in waveguide-confined (WC) anti-symmetric
modes of hexagonal plasmonic crystals in InP-TiO-Au-TiO-Si heterostructures.
The radiative decay time of the InP-based transverse magnetic (TM)-strained
multi-quantum well (MQW) coupled to the SPP modes is observed to be 2.9-3.7
times shorter than that of a bare MQW wafer. Theoretically we find that 80 % of
the enhanced PL is emitted into SPP modes, and 17 % of the enhanced
luminescence is redirected into WC-anti-symmetric modes. In addition to the
direct coupling of the excitons to the plasmonic modes, this demonstration is
also useful for the development of high-temperature SPP lasers, the development
of highly integrated photo-electrical devices, or miniaturized biosensors.Comment: Spontaneous emission control in high-extraction efficiency plasmonic
crystal
Solvable PT-symmetric model with a tunable interspersion of non-merging levels
We study the spectrum in such a PT-symmetric square well of a diameter L
where the "strength of the non-Hermiticity" is controlled by the two
parameters, viz., by an imaginary coupling ig and by the distance d of its
onset from the origin. We solve this problem and confirm that the spectrum is
discrete and real in a non-empty interval of g. Surprisingly, a specific
distinction between the bound states is found in their asymptotic
stability/instability with respect to an unlimited growth of g. In our model,
all of the low-lying levels remain asymptotically unstable at the small d and
finite L while only the stable levels survive for d near L or in the purely
imaginary well with infinite L. In between these two extremes, an unusual and
tunable, variable pattern of the interspersed "robust" and "fragile" subspectra
of the real levels is obtained.Comment: final version: 33 pages (plus the old 8 figures of version 1
Zero forcing number, constrained matchings and strong structural controllability
The zero forcing number is a graph invariant introduced to study the minimum
rank of the graph. In 2008, Aazami proved the NP-hardness of computing the zero
forcing number of a simple undirected graph. We complete this NP-hardness
result by showing that the non-equivalent problem of computing the zero forcing
number of a directed graph allowing loops is also NP-hard. The rest of the
paper is devoted to the strong controllability of a networked system. This kind
of controllability takes into account only the structure of the interconnection
graph, but not the interconnection strengths along the edges. We provide a
necessary and sufficient condition in terms of zero forcing sets for the strong
controllability of a system whose underlying graph is a directed graph allowing
loops. Moreover, we explain how our result differs from a recent related result
discovered by Monshizadeh et al. Finally, we show how to solve the problem of
finding efficiently a minimum-size input set for the strong controllability of
a self-damped system with a tree-structure.Comment: Submitted as a journal paper in May 201
Photon engineering for quantum information processing
We study distinguishing information in the context of quantum interference
involving more than one parametric downconversion (PDC) source and in the
context of polarization-entangled photon pairs based on PDC. We arrive at
specific design criteria for two-photon sources so that when used as part of
complex optical systems, such as photon-based quantum information processing
schemes, distinguishing information between the photons is eliminated
guaranteeing high visibility interference. We propose practical techniques
which lead to suitably engineered two-photon states that can be realistically
implemented with available technology. Finally, we study an implementation of
the nonlinear-sign shift (NS) logic gate with PDC sources and show the effect
of distinguishing information on the performance of the gate.Comment: 23 pages, 13 figures. submitted to Quantum Information & Computatio
Coherent perfect absorption in photonic structures
The ability to drive a system with an external input is a fundamental aspect
of light-matter interaction. The coherent perfect absorption (CPA) phenomenon
extends to the general multibeam interference phenomenology the well known
critical coupling concepts. This interferometric control of absorption can be
employed to reach full delivery of optical energy to nanoscale systems such as
plasmonic nanoparticles, and multi-port interference can be used to enhance the
absorption of a nanoscale device when it is embedded in a strongly scattering
system, with potential applications to nanoscale sensing. Here we review the
two-port CPA in reference to photonic structures which can resonantly couple to
the external fields. A revised two-port theory of CPA is illustrated, which
relies on the Scattering Matrix formalism and is valid for all linear two-port
systems with reciprocity. Through a semiclassical approach, treating two-port
critical coupling conditions in a non-perturbative regime, it is demonstrated
that the strong coupling regime and the critical coupling condition can indeed
coexist; in this situation, termed strong critical coupling, all the incoming
energy is converted into polaritons. Experimental results are presented, which
clearly display the elliptical trace of absorption as function of input
unbalance in a thin metallo-dielectric metamaterial, and verify polaritonic CPA
in an intersubband-polariton photonic-crystal membrane resonator. Concluding
remarks discuss the future perspectives of CPA with photonic structures.Comment: arXiv admin note: substantial text overlap with arXiv:1605.0890
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