25,957 research outputs found
Design of Strict Control-Lyapunov Functions for Quantum Systems with QND Measurements
We consider discrete-time quantum systems subject to Quantum Non-Demolition
(QND) measurements and controlled by an adjustable unitary evolution between
two successive QND measures. In open-loop, such QND measurements provide a
non-deterministic preparation tool exploiting the back-action of the
measurement on the quantum state. We propose here a systematic method based on
elementary graph theory and inversion of Laplacian matrices to construct strict
control-Lyapunov functions. This yields an appropriate feedback law that
stabilizes globally the system towards a chosen target state among the
open-loop stable ones, and that makes in closed-loop this preparation
deterministic. We illustrate such feedback laws through simulations
corresponding to an experimental setup with QND photon counting
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Highly Stable Luminous "snakes" from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires
CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material's instability toward polar solvents, heat, or UV irradiation greatly limits its further applications. Herein, an efficient in situ growing strategy has been developed to give highly stable perovskite NC composites (abbreviated CsPbX3@CA-SiO2) by anchoring CsPbX3 NCs onto silica nanowires (NWs), which effectively depresses the optical degradation of their photoluminescence (PL) and enhances stability. The preparation of surface-functionalized serpentine silica NWs is realized by a sol-gel process involving hydrolysis of a mixture of tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), and trimethoxy(octadecyl)silane (TMODS) in a water/oil emulsion. The serpentine NWs are formed via an anisotropic growth with lengths up to 8 ÎŒm. The free amino groups are employed as surface ligands for growing perovskite NCs, yielding distributed monodisperse NCs (âŒ8 nm) around the NW matrix. The emission wavelength is tunable by simple variation of the halide compositions (CsPbX3, X = Cl, Br, or I), and the composites demonstrate a high photoluminescence quantum yield (PLQY 32-69%). Additionally, we have demonstrated the composites CsPbX3@CA-SiO2 can be self-woven to form a porous 3D hierarchical NWs membrane, giving rise to a superhydrophobic surface with hierarchical micro/nano structural features. The resulting composites exhibit high stability toward water, heat, and UV irradiation. This work elucidates an effective strategy to incorporate perovskite nanocrystals onto functional matrices as multifunctional stable light sources
Delayed feedback control in quantum transport
Feedback control in quantum transport has been predicted to give rise to
several interesting effects, amongst them quantum state stabilisation and the
realisation of a mesoscopic Maxwell's daemon. These results were derived under
the assumption that control operations on the system be affected
instantaneously after the measurement of electronic jumps through it. In this
contribution I describe how to include a delay between detection and control
operation in the master equation theory of feedback-controlled quantum
transport. I investigate the consequences of delay for the state-stabilisation
and Maxwell's-daemon schemes. Furthermore, I describe how delay can be used as
a tool to probe coherent oscillations of electrons within a transport system
and how this formalism can be used to model finite detector bandwidth.Comment: 13 pages, 5 figure
Metastable Quivers in String Compactifications
We propose a scenario for dynamical supersymmetry breaking in string
compactifications based on geometric engineering of quiver gauge theories. In
particular we show that the runaway behavior of fractional branes at del Pezzo
singularities can be stabilized by a flux superpotential in compact models. Our
construction relies on homological mirror symmetry for orientifolds.Comment: 22 pages, 1 figure; v2: references adde
Quantum field inspired model of decision making: Asymptotic stabilization of belief state via interaction with surrounding mental environment
This paper is devoted to justification of the quantum-like model of the process of decision making based on theory of open quantum systems: decision making as decoher- ence. This process is modeled as interaction of a decision maker, Alice, with a mental (information) environment R surrounding her. Such an interaction generates âdissipation of uncertaintyâ from Aliceâs belief-state Ï ( t ) into R and asymptotic stabilization of Ï ( t ) to a steady belief-state. The latter is treated as the decision state. Mathematically the problem under study is about finding constraints on R guaranteeing such stabilization. We found a partial solution of this problem (in the form of sufficient conditions). We present the corresponding decision making analysis for one class of mental environments, so-called âalmost homogeneous environmentsâ, with the illustrative examples: a) behavior of electorate interacting with the mass-media âreservoirâ; b) consumersâ persuasion. We also comment on other classes of mental environments
Stability Conditions, Wall-crossing and weighted Gromov-Witten Invariants
We extend B. Hassett's theory of weighted stable pointed curves ([Has03]) to
weighted stable maps. The space of stability conditions is described
explicitly, and the wall-crossing phenomenon studied. This can be considered as
a non-linear analog of the theory of stability conditions in abelian and
triangulated categories.
We introduce virtual fundamental classes and thus obtain weighted
Gromov-Witten invariants. We show that by including gravitational descendants,
one obtains an \LL-algebra as introduced in [LM04] as a generalization of a
cohomological field theory.Comment: 28 pages; v2: references added and updated, addressed referee
comments; to appear in Moscow Math Journa
Strictly contractive quantum channels and physically realizable quantum computers
We study the robustness of quantum computers under the influence of errors
modelled by strictly contractive channels. A channel is defined to be
strictly contractive if, for any pair of density operators in its
domain, for some (here denotes the trace norm). In other words, strictly
contractive channels render the states of the computer less distinguishable in
the sense of quantum detection theory. Starting from the premise that all
experimental procedures can be carried out with finite precision, we argue that
there exists a physically meaningful connection between strictly contractive
channels and errors in physically realizable quantum computers. We show that,
in the absence of error correction, sensitivity of quantum memories and
computers to strictly contractive errors grows exponentially with storage time
and computation time respectively, and depends only on the constant and the
measurement precision. We prove that strict contractivity rules out the
possibility of perfect error correction, and give an argument that approximate
error correction, which covers previous work on fault-tolerant quantum
computation as a special case, is possible.Comment: 14 pages; revtex, amsfonts, amssymb; made some changes (recommended
by Phys. Rev. A), updated the reference
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