3,860 research outputs found
A 3D topological insulator quantum dot for optically controlled quantum memory and quantum computing
We present the model of a quantum dot (QD) consisting of a spherical
core-bulk heterostructure made of 3D topological insulator (TI) materials, such
as PbTe/PbSnTe, with bound massless and helical Weyl states
existing at the interface and being confined in all three dimensions. The
number of bound states can be controlled by tuning the size of the QD and the
magnitude of the core and bulk energy gaps, which determine the confining
potential. We demonstrate that such bound Weyl states can be realized for QD
sizes of few nanometers. We identify the spin locking and the Kramers pairs,
both hallmarks of 3D TIs. In contrast to topologically trivial semiconductor
QDs, the confined massless Weyl states in 3D TI QDs are localized at the
interface of the QD and exhibit a mirror symmetry in the energy spectrum. We
find strict optical selection rules satisfied by both interband and intraband
transitions that depend on the polarization of electron-hole pairs and
therefore give rise to the Faraday effect due to Pauli exclusion principle. We
show that the semi-classical Faraday effect can be used to read out spin
quantum memory. When a 3D TI QD is embedded inside a cavity, the single-photon
Faraday rotation provides the possibility to implement optically mediated
quantum teleportation and quantum information processing with 3D TI QDs, where
the qubit is defined by either an electron-hole pair, a single electron spin,
or a single hole spin in a 3D TI QD. Remarkably, the combination of inter- and
intraband transition gives rise to a large dipole moment of up to 450 Debye.
Therefore, the strong-coupling regime can be reached for a cavity quality
factor of in the infrared wavelength regime of around
m.Comment: 19 pages, 11 figures, RevTe
Continuous-variable entanglement distillation over a pure loss channel with multiple quantum scissors
Entanglement distillation is a key primitive for distributing high-quality
entanglement between remote locations. Probabilistic noiseless linear
amplification based on the quantum scissors is a candidate for entanglement
distillation from noisy continuous-variable (CV) entangled states. Being a
non-Gaussian operation, quantum scissors is challenging to analyze. We present
a derivation of the non-Gaussian state heralded by multiple quantum scissors in
a pure loss channel with two-mode squeezed vacuum input. We choose the reverse
coherent information (RCI)---a proven lower bound on the distillable
entanglement of a quantum state under one-way local operations and classical
communication (LOCC), as our figure of merit. We evaluate a Gaussian lower
bound on the RCI of the heralded state. We show that it can exceed the
unlimited two-way LOCCassisted direct transmission entanglement distillation
capacity of the pure loss channel. The optimal heralded Gaussian RCI with two
quantum scissors is found to be significantly more than that with a single
quantum scissors, albeit at the cost of decreased success probability. Our
results fortify the possibility of a quantum repeater scheme for CV quantum
states using the quantum scissors.Comment: accepted for publication in Physical Review
A New Relation between post and pre-optimal measurement states
When an optimal measurement is made on a qubit and what we call an Unbiased
Mixture of the resulting ensembles is taken, then the post measurement density
matrix is shown to be related to the pre-measurement density matrix through a
simple and linear relation. It is shown that such a relation holds only when
the measurements are made in Mutually Unbiased Bases- MUB. For Spin-1/2 it is
also shown explicitly that non-orthogonal measurements fail to give such a
linear relation no matter how the ensembles are mixed. The result has been
proved to be true for arbitrary quantum mechanical systems of finite
dimensional Hilbert spaces. The result is true irrespective of whether the
initial state is pure or mixed.Comment: 4 pages in REVTE
Axial range of conjugate adaptive optics in two-photon microscopy
We describe an adaptive optics technique for two-photon microscopy in which
the deformable mirror used for aberration compensation is positioned in a plane
conjugate to the plane of the aberration. We demonstrate in a
proof-of-principle experiment that this technique yields a large field of view
advantage in comparison to standard pupil-conjugate adaptive optics. Further,
we show that the extended field of view in conjugate AO is maintained over a
relatively large axial translation of the deformable mirror with respect to the
conjugate plane. We conclude with a discussion of limitations and prospects for
the conjugate AO technique in two-photon biological microscopy
Evaluating the Roles of Rainout and Post-Condensation Processes in a Landfalling Atmospheric River with Stable Isotopes in Precipitation and Water Vapor
Atmospheric rivers (ARs), and frontal systems more broadly, tend to exhibit prominent “V” shapes in time series of stable isotopes in precipitation. Despite the magnitude and widespread nature of these “V” shapes, debate persists as to whether these shifts are driven by changes in the degree of rainout, which we determine using the Rayleigh distillation of stable isotopes, or by post-condensation processes such as below-cloud evaporation and equilibrium isotope exchange between hydrometeors and surrounding vapor. Here, we present paired precipitation and water vapor isotope time series records from the 5–7 March 2016, AR in Bodega Bay, CA. The stable isotope composition of surface vapor along with independent meteorological constraints such as temperature and relative humidity reveal that rainout and post-condensation processes dominate during different portions of the event. We find that Rayleigh distillation controls during peak AR conditions (with peak rainout of 55%) while post-condensation processes have their greatest effect during periods of decreased precipitation on the margins of the event. These results and analyses inform critical questions regarding the temporal evolution of AR events and the physical processes that control them at local scales
A Multi-Objective Decision-Making Approach For Mutual Fund Portfolio
Investment decision-making problems are generally multi-objective in nature such as minimization of the risk and maximization of the expected return. These problems can be solved efficiently and effectively using multi-objective decision making (MODM) tools such as a lexicographic goal programming (LGP). This paper applies the LGP model for selecting an optimum mutual fund portfolio for an investor, while taking into account specific parameters including risk, return, expense ratio and others. Sensitivity analysis on the assigned weights in a priority structure of the goals identifies all possible solutions for decision-making. The Euclidean distance method is then used, to measure distances of all possible solutions from the identified ideal solution. The optimal solution is determined by the minimum distance between the ideal solution and other possible solutions of the problem. The associated weights with the optimal solution will be the most appropriate weights in a given priority structure. The effectiveness and applicability of the LGP model is demonstrated via a case example from broad categories of mutual funds
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