8,639 research outputs found
Resonance fluorescence beyond the dipole approximation of a quantum dot in a plasmonic nanostructure
The mesoscopic characteristics of a quantum dot (QD), which make the dipole
approximation (DA) break down, provide a new dimension to manipulate
light-matter interaction [M. L. Andersen et al., Nat. Phys. 7, 215 (2011)].
Here we investigate the power spectrum and the second-order correlation
property of the fluorescence from a resonantly driven QD placed on a planar
metal. It is revealed that due to the pronounced QD spatial extension and the
dramatic variation of the triggered surface plasmon near the metal, the
fluorescence has a notable contribution from the quadrupole moment. The
{\pi}-rotation symmetry of the fluorescence to the QD orientation under the DA
is broken. By manipulating the QD orientation and quadrupole moment, the
spectrum can be switched between the Mollow triplet and a single peak, and the
fluorescence characterized by the antibunching in the second-order correlation
function can be changed from the weak to the strong radiation regime. Our
result is instructive for utilizing the unique mesoscopic effects to develop
nanophotonic devices
Generation of stable entanglement between two cavity mirrors by squeezed-reservoir engineering
The generation of quantum entanglement of macroscopic or mesoscopic bodies in
mechanical motion is generally bounded by the thermal fluctuation exerted by
their environments. Here we propose a scheme to establish stationary
entanglement between two mechanically oscillating mirrors of a cavity. It is
revealed that, by applying a broadband squeezed laser acting as a
squeezed-vacuum reservoir to the cavity, a stable entanglement between the
mechanical mirrors can be generated. Using the adiabatic elimination and master
equation methods, we analytically find that the generated entanglement is
essentially determined by the squeezing of the relative momentum of the
mechanical mirrors, which is transferred from the squeezed reservoir through
the cavity. Numerical verification indicates that our scheme is within the
present experimental state of the art of optomechanics.Comment: 9 pages, 6 figure
Coupled Cluster Treatment of the Alternating Bond Diamond Chain
By the analytical coupled cluster method (CCM), we study both the ground
state and lowest-lying excited-state properties of the alternating bond diamond
chain. The numerical exact diagonalization (ED) method is also applied to the
chain to verify the accuracy of CCM results. The ED results show that the
ground-state phase diagram contains two exact spin cluster solid ground states,
namely, the tetramer-dimer (TD) state and dimer state, and the ferrimagnetic
long-range-ordered state. We prove that the two exact spin cluster solid ground
states can both be formed by CCM. Moreover, the exact spin gap in the TD state
can be obtained by CCM. In the ferrimagnetic region, we find that the CCM
results for some physical quantities, such as the ground-state energy, the
sublattice magnetizations, and the antiferromagnetic gap, are comparable to the
results obtained by numerical methods. The critical line dividing the TD state
from the ferrimagnetic state is also given by CCM and is in perfect agreement
with that determined by the ED method.Comment: arXiv admin note: text overlap with arXiv:1502.0680
Exact decoherence-free state of two distant quantum systems in a non-Markovian environment
Decoherence-free state (DFS) encoding supplies a useful way to avoid the
detrimental influence of the environment on quantum information processing. The
DFS was previously well established in either the two subsystems locating at
the same spatial position or the dynamics under the Born--Markovian
approximation. Here, we investigate the exact DFS of two spatially separated
quantum systems consisting of two-level systems or harmonic oscillators coupled
to a common non-Markovian zero-temperature bosonic environment. The exact
distance-dependent DFS and the explicit criterion for forming the DFS are
obtained analytically, which reveals that the DFS can arise only in
one-dimensional environment. It is remarkable to further find that the DFS is
just the system-reduced state of the famous bound state in the continuum (BIC)
of the total system predicted by Wigner and von Neumann. On the one hand our
result gives insight into the physical nature of the DFS, and on the other hand
it supplies an experimentally accessible scheme to realize the mathematically
curious BIC in the standard quantum optical systems.Comment: 7 pages, 3 figure
Towards A Deep Insight into Landmark-based Visual Place Recognition: Methodology and Practice
In this paper, we address the problem of landmark-based visual place
recognition. In the state-of-the-art method, accurate object proposal
algorithms are first leveraged for generating a set of local regions containing
particular landmarks with high confidence. Then, these candidate regions are
represented by deep features and pairwise matching is performed in an
exhaustive manner for the similarity measure. Despite its success, conventional
object proposal methods usually produce massive landmark-dependent image
patches exhibiting significant distribution variance in scale and overlap. As a
result, the inconsistency in landmark distributions tends to produce biased
similarity between pairwise images yielding the suboptimal performance. In
order to gain an insight into the landmark-based place recognition scheme, we
conduct a comprehensive study in which the influence of landmark scales and the
proportion of overlap on the recognition performance is explored. More
specifically, we thoroughly study the exhaustive search based landmark matching
mechanism, and thus derive three-fold important observations in terms of the
beneficial effect of specific landmark generation strategies. Inspired by the
above observations, a simple yet effective dense sampling based scheme is
presented for accurate place recognition in this paper. Different from the
conventional object proposal strategy, we generate local landmarks of multiple
scales with uniform distribution from entire image by dense sampling, and
subsequently perform multi-scale fusion on the densely sampled landmarks for
similarity measure. The experimental results on three challenging datasets
demonstrate that the recognition performance can be significantly improved by
our efficient method in which the landmarks are appropriately produced for
accurate pairwise matching
Quantum entanglement and teleportation in quantum dot
We study the thermal entanglement and quantum teleportation using quantum dot
as a resource. We first consider entanglement of the resource, and then focus
on the effects of different parameters on the teleportation fidelity under
different conditions. The critical temperature of disentanglement is obtained.
Based on Bell measurements in two subspaces, we find the anisotropy
measurements is optimal to the isotropy arising from the entangled eigenstates
of the system in the anisotropy subspace. In addition, it is shown that the
anisotropy transmission fidelity is very high and stable for quantum dot as
quantum channel when the parameters are adjusted. The possible applications of
quantum dot are expected in the quantum teleportation
Quasiparticle Band Gaps, Excitonic Effects, and Anisotropic Optical Properties of Monolayer Distorted 1-T Diamond-chain Structures
We report many-body perturbation theory calculations of excited-state
properties of distorted 1-T diamond-chain monolayer rhenium disulfide (ReS2)
and diselenide (ReSe2). Electronic self-energy substantially enhances their
quasiparticle band gaps and, surprisingly, converts monolayer ReSe2 to a
direct-gap semiconductor, which was, however, regarded to be an indirect one by
density-functional-theory calculations. Their optical absorption spectra are
dictated by strongly bound excitons. Unlike hexagonal structures, the
lowest-energy bright exciton of distorted 1-T ReS2 exhibits a perfect figure-8
shape polarization dependence but those of ReSe2 only exhibit a partial
polarization dependence, which results from two nearly-degenerated bright
excitons whose polarization preferences are not aligned. Our first-principles
calculations are in agreement with experiments and pave the way for
optoelectronic applications
Analytical and numerical studies of the one-dimensional sawtooth chain
By using the analytical coupled cluster method, the numerical exact
diagonalization method, and the numerical density matrix renormalization group
method, we investigated the properties of the one-dimensional sawtooth chain.
The results of the coupled cluster method based on Neel state demonstrate that
the ground state is in the quasi-Neel-long-range order state when a<ac1. The
translational symmetry of the ground state varies and the ground state evolves
from the quasi-Neel-long-range order state to the dimerized state at the
critical point ac1. The dimerized state is stable in the intermediate parameter
regime and vanishes at another critical point ac2. The results drawn from the
exact diagonalization show that the precise critical point ac1 and ac2 can be
determined by using the spin stiffness fidelity susceptibility and spin gap
separately. We compared the results obtained by using the coupled cluster
method based on canted state with those obtained based on spiral state, and
found that the ground state of the sawtooth chain is in the quasi-canted state
if a>ac2. The results of the coupled cluster method and the density matrix
renormalization group method both disclose that the type of the quantum phase
transition occurring at ac2 belongs to the first-order transition.Comment: accepted versio
Canonical versus noncanonical equilibration dynamics of open quantum systems
In statistical mechanics, any quantum system in equilibrium with its weakly
coupled reservoir is described by a canonical state at the same temperature as
the reservoir. Here, by studying the equilibration dynamics of a harmonic
oscillator interacting with a reservoir, we evaluate microscopically the
condition under which the equilibration to a canonical state is valid. It is
revealed that the non-Markovian effect and the availability of a stationary
state of the total system play a profound role in the equilibration. In the
Markovian limit, the conventional canonical state can be recovered. In the
non-Markovian regime, when the stationary state is absent, the system
equilibrates to a generalized canonical state at an effective temperature;
whenever the stationary state is present, the equilibrium state of the system
cannot be described by any canonical state anymore. Our finding of the physical
condition on such noncanonical equilibration might have significant impact on
statistical physics. A physical scheme based on circuit QED is proposed to test
our results
A Model for the Coexistence of p-wave Superconductivity and Ferroelectricity
A model for the coexistence of p-wave superconductivity (SC) and
ferroelectricity (FE) is presented. The Hamiltonian of SC sector and FE sector
can be diagonalized by using the and algebraic coherent states
respectively. We assume a minimal symmetry-allow coupling and simplify the
total Hamiltonian through a double mean-field approximation (DMFA).
A variational coherent-state (VCS) trial wave-function is applied for the
ground state. It is found that the ferroelectricity gives rise to the magnetic
field effect of p-wave superconductivity.Comment: 11pages,no figur
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