60 research outputs found
Plasmon Injection to Compensate and Control Losses in Negative Index Metamaterials
Metamaterials have introduced a whole new world of unusual materials with
functionalities that cannot be attained in naturally occurring material systems
by mimicking and controlling the natural phenomena at subwavelength scales.
However, the inherent absorption losses pose fundamental challenge to the most
fascinating applications of metamaterials. Based on a novel plasmon injection
(PI or \Pi) scheme, we propose a coherent optical amplification technique to
compensate losses in metamaterials. Although the proof of concept device here
operates under normal incidence only, our proposed scheme can be generalized to
arbitrary form of incident waves. The \Pi-scheme is fundamentally different
than major optical amplification schemes. It does not require gain medium,
interaction with phonons, or any nonlinear medium. The \Pi-scheme allows for
loss-free metamaterials. It is ideally suited for mitigating losses in
metamaterials operating in the visible spectrum and is scalable to other
optical frequencies. These findings open the possibility of reviving the early
dreams of making 'magical' metamaterials from scratch.Comment: Main text, 8 pages with 4 figures; supplemental material, 21 pages
with 21 figure
Liouvillian Exceptional Points of Non-Hermitian Systems via Quantum Process Tomography
Hamiltonian exceptional points (HEPs) are spectral degeneracies of
non-Hermitian Hamiltonians describing classical and semiclassical open systems
with gain and/or loss. However, this definition overlooks the occurrence of
quantum jumps in the evolution of open quantum systems. These quantum effects
are properly accounted for by considering Liouvillians and their exceptional
points (LEPs) [Minganti et al., Phys. Rev. A {\bf 100}, 062131 (2019)]. Here,
we explicitly describe how standard quantum process tomography, which reveals
the dynamics of a quantum system, can be readily applied to reveal and
characterize LEPs of non-Hermitian systems. We conducted experiments on an IBM
quantum processor to implement a prototype model simulating the decay of a
single qubit through three competing channels. Subsequently, we performed
tomographic reconstruction of the corresponding experimental Liouvillians and
their LEPs using both single- and two-qubit operations. This example
underscores the efficacy of process tomography in tuning and observing LEPs,
despite the absence of HEPs in the model.Comment: 9+17 pages, 2+4 figure
Geometry of the Field-Moment Spaces for Quadratic Bosonic Systems: Diabolically Degenerated Exceptional Points on Complex -Polytopes
-Polytopes are a generalization of polyhedra in dimensions. Here, we
show that complex -polytopes naturally emerge in the higher-order field
moments spaces of quadratic bosonic systems, thus revealing their geometric
character. In particular, a complex-valued evolution matrix, governing the
dynamics of th-order field moments of a bosonic dimer, can describe a
complex -dimensional hypercube. The existence of such -polytopes is
accompanied by the presence of high-order diabolic points (DPs). Interestingly,
when the field-moment space additionally exhibits exceptional points (EPs), the
formation of -polytopes may lead to the emergence of diabolically
degenerated EPs, due to the interplay between DPs and EPs. Such intriguing
spectral properties of complex polytopes may enable constructing photonic
lattice systems with similar spectral features in real space. Our results can
be exploited in various quantum protocols based on EPs, paving a new direction
of research in this field.Comment: 9 page
Restoring Adiabatic State Transfer in Time-Modulated Non-Hermitian Systems
Non-Hermitian systems have attracted much interest in recent decades, driven
partly by the existence of exotic spectral singularities, known as exceptional
points (EPs), where the dimensionality of the system evolution operator is
reduced. Among various intriguing applications, the discovery of EPs has
suggested the potential for implementing a symmetric mode switch, when
encircling them in a system parameter space. However, subsequent theoretical
and experimental works have revealed that {\it dynamical} encirclement of EPs
invariably results in asymmetric mode conversion; namely, the mode switching
depends only on the winding direction but not on the initial state. This
chirality arises from the failure of adiabaticity due to the complex spectrum
of non-Hermitian systems. Although the chirality revealed has undoubtedly made
a significant impact in the field, a realization of the originally sought
symmetric adiabatic passage in non-Hermitian systems with EPs has since been
elusive. In this work, we bridge this gap and theoretically demonstrate that
adiabaticity, and therefore a symmetric state transfer, is achievable when
dynamically winding around an EP. This becomes feasible by specifically
choosing a trajectory in the system parameter space along which the
corresponding evolution operator attains a real spectrum. Our findings, thus,
offer a promise for advancing various wave manipulation protocols in both
quantum and classical domains.Comment: 6 pages, 4 figure
Kraus representation of damped harmonic oscillator and its application
By definition, the Kraus representation of a harmonic oscillator suffering
from the environment effect, modeled as the amplitude damping or the phase
damping, is directly given by a simple operator algebra solution. As examples
and applications, we first give a Kraus representation of a single qubit whose
computational basis states are defined as bosonic vacuum and single particle
number states. We further discuss the environment effect on qubits whose
computational basis states are defined as the bosonic odd and even coherent
states. The environment effects on entangled qubits defined by two different
kinds of computational basis are compared with the use of fidelity.Comment: 9 pages, 3 figure
Dynamics of entanglement for coherent excitonic states in a system of two coupled quantum dots and cavity QED
The dynamics of the entanglement for coherent excitonic states in the system
of two coupled large semiconductor quantum dots () mediated by a
single-mode cavity field is investigated. Maximally entangled coherent
excitonic states can be generated by cavity field initially prepared in odd
coherent state. The entanglement of the excitonic coherent states between two
dots reaches maximum when no photon is detected in the cavity. The effects of
the zero-temperature environment on the entanglement of excitonic coherent
state are also studied using the concurrence for two subsystems of the excitonsComment: 7 pages, 6 figure
Size-dependent decoherence of excitonic states in semiconductor microcrystallites
The size-dependent decoherence of the exciton states resulting from the
spontaneous emission is investigated in a semiconductor spherical
microcrystallite under condition . In general, the
larger size of the microcrystallite corresponds to the shorter coherence time.
If the initial state is a superposition of two different excitonic coherent
states, the coherence time depends on both the overlap of two excitonic
coherent states and the size of the microcrystallite. When the system with
fixed size is initially in the even or odd coherent states, the larger average
number of the excitons corresponds to the faster decoherence. When the average
number of the excitons is given, the bigger size of the microcrystallite
corresponds to the faster decoherence. The decoherence of the exciton states
for the materials GaAs and CdS is numerically studied by our theoretical
analysis.Comment: 4 pages, two figure
Quantum Statistics of Surface Plasmon Polaritons in Metallic Stripe Waveguides
Single surface plasmon polaritons are excited using photons generated via
spontaneous parametric down-conversion. The mean excitation rates, intensity
correlations and Fock state populations are studied. The observed dependence of
the second order coherence in our experiment is consistent with a linear
uncorrelated Markovian environment in the quantum regime. Our results provide
important information about the effect of loss for assessing the potential of
plasmonic waveguides for future nanophotonic circuitry in the quantum regime.Comment: 21 pages, 6 figures, published in Nano Letters, publication date
(web): March 27 (2012
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