37,479 research outputs found
Operational Entanglement Families of Symmetric Mixed N-Qubit States
We introduce an operational entanglement classification of symmetric mixed
states for an arbitrary number of qubits based on stochastic local operations
assisted with classical communication (SLOCC operations). We define families of
SLOCC entanglement classes successively embedded into each other, we prove that
they are of non-zero measure, and we construct witness operators to distinguish
them. Moreover, we discuss how arbitrary symmetric mixed states can be realized
in the lab via a one-to-one correspondence between well-defined sets of
controllable parameters and the corresponding entanglement families.Comment: 6 pages, 2 figures, published version, Phys. Rev. A, in pres
Overcoming a limitation of deterministic dense coding with a non-maximally entangled initial state
Under two-party deterministic dense-coding, Alice communicates (perfectly
distinguishable) messages to Bob via a qudit from a pair of entangled qudits in
pure state |Psi>. If |Psi> represents a maximally entangled state (i.e., each
of its Schmidt coefficients is sqrt(1/d)), then Alice can convey to Bob one of
d^2 distinct messages. If |Psi> is not maximally entangled, then Ji et al.
[Phys. Rev. A 73, 034307 (2006)] have shown that under the original
deterministic dense-coding protocol, in which messages are encoded by unitary
operations performed on Alice's qudit, it is impossible to encode d^2-1
messages. Encoding d^2-2 is possible; see, e.g., the numerical studies by Mozes
et al. [Phys. Rev. A 71, 012311 (2005)]. Answering a question raised by Wu et
al. [Phys. Rev. A 73, 042311 (2006)], we show that when |Psi> is not maximally
entangled, the communications limit of d^2-2 messages persists even when the
requirement that Alice encode by unitary operations on her qudit is weakened to
allow encoding by more general quantum operators. We then describe a
dense-coding protocol that can overcome this limitation with high probability,
assuming the largest Schmidt coefficient of |Psi> is sufficiently close to
sqrt(1/d). In this protocol, d^2-2 of the messages are encoded via unitary
operations on Alice's qudit, and the final (d^2-1)-th message is encoded via a
(non-trace-preserving) quantum operation.Comment: 18 pages, published versio
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A comparison of in-sample forecasting methods
In-sample forecasting is a recent continuous modification of well-known forecasting methods based on aggregated data. These aggregated methods are known as age-cohort methods in demography, economics, epidemiology and sociology and as chain ladder in non-life insurance. Data is organized in a two-way table with age and cohort as indices, but without measures of exposure. It has recently been established that such structured forecasting methods based on aggregated data can be interpreted as structured histogram estimators. Continuous in-sample forecasting transfers these classical forecasting models into a modern statistical world including smoothing methodology that is more efficient than smoothing via histograms. All in-sample forecasting estimators are collected and their performance is compared via a finite sample simulation study. All methods are extended via multiplicative bias correction. Asymptotic theory is being developed for the histogram-type method of sieves and for the multiplicatively corrected estimators. The multiplicative bias corrected estimators improve all other known in-sample forecasters in the simulation study. The density projection approach seems to have the best performance with forecasting based on survival densities being the runner-up
Option Pricing in Multivariate Stochastic Volatility Models of OU Type
We present a multivariate stochastic volatility model with leverage, which is
flexible enough to recapture the individual dynamics as well as the
interdependencies between several assets while still being highly analytically
tractable.
First we derive the characteristic function and give conditions that ensure
its analyticity and absolute integrability in some open complex strip around
zero. Therefore we can use Fourier methods to compute the prices of multi-asset
options efficiently. To show the applicability of our results, we propose a
concrete specification, the OU-Wishart model, where the dynamics of each
individual asset coincide with the popular Gamma-OU BNS model. This model can
be well calibrated to market prices, which we illustrate with an example using
options on the exchange rates of some major currencies. Finally, we show that
covariance swaps can also be priced in closed form.Comment: 28 pages, 5 figures, to appear in SIAM Journal on Financial
Mathematic
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Generalised additive dependency inflated models including aggregated covariates
Let us assume that X, Y and U are observed and that the conditional mean of U given X and Y can be expressed via an additive dependency of X, λ(X)Y and X + Y for some unspecified function . This structured regression model can be transferred to a hazard model or a density model when applied on some appropriate grid, and has important forecasting applications via structured marker dependent hazards models or structured density models including age-period-cohort relationships. The structured regression model is also important when the severity of the dependent variable has a complicated dependency on waiting times X, Y and the total waiting time X+Y . In case the conditional mean of U approximates a density, the regression model can be used to analyse the age-period-cohort model, also when exposure data are not available. In case the conditional mean of U approximates a marker dependent hazard, the regression model introduces new relevant age-period-cohort time scale interdependencies in understanding longevity. A direct use of the regression relationship introduced in this paper is the estimation of the severity of outstanding liabilities in non-life insurance companies. The technical approach taken is to use B-splines to capture the underlying one-dimensional unspecified functions. It is shown via finite sample simulation studies and an application for forecasting future asbestos related deaths in the UK that the B-spline approach works well in practice. Special consideration has been given to ensure identifiability of all models considered
On the energy dependence of the D^+/D^- production asymmetry
In this paper we discuss the origin of the asymmetry present in D meson
production and its energy dependence. In particular, we have applied the meson
cloud model to calculate the asymmetries in D^-/D^+ meson production in high
energy p-p collisions and find a good agreement with recent LHCb data. Although
small, this non-vanishing asymmetry may shed light on the role played by the
charm meson cloud of the proton.Comment: 8 pages, 8 figures. arXiv admin note: text overlap with
arXiv:hep-ph/000927
Reconceptualising Personas Across Cultures: Archetypes, Stereotypes & Collective Personas in Pastoral Namibia
The paucity of projects where persona is the research foci and a lack of consensus on this artefact keep many reticent about its purpose and value. Besides crafting personas is expected to differ across cultures, which contrasts the advancements in Western theory with studies and progress in other sites. We postulate User-Created Personas reveal specific characteristics of situated contexts by allowing laypeople to design persona artefacts in their own terms. Hence analysing four persona sessions with an ethnic group in pastoral Namibia –ovaHerero– brought up a set of fundamental questions around the persona artefact regarding stereotypes, archetypes, and collective persona representations: (1) to what extent user depictions are stereotypical or archetypal? If stereotypes prime (2) to what degree are current personas a useful method to represent end-users in technology design? And, (3) how can we ultimately read accounts not conforming to mainstream individual persona descriptions but to collectives
Characterization of the Sequential Product on Quantum Effects
We present a characterization of the standard sequential product of quantum
effects. The characterization is in term of algebraic, continuity and duality
conditions that can be physically motivated.Comment: 11 pages. Accepted for publication in the Journal of Mathematical
Physic
Multipartite entanglement in the Fenna-Matthews-Olson (FMO) pigment-protein complex
We investigate multipartite states in the Fenna-Matthews-Olson (FMO)
pigment-protein complex of the green sulfur bacteria using a Lorentzian
spectral density of the phonon reservoir fitted with typical parameter
estimates of the species, P. aestuarii. The evolution of the entanglement
measure of the excitonic W qubit states is evaluated in the picosecond time
range, showing increased revivals in the non-Markovian regime. Similar trends
are observed in the evolution dynamics of the Meyer-Wallach measure of the
N-exciton multipartite state, with results showing that multipartite
entanglement can last from 0.5 to 1 ps, between the Bchls of the FMO complex.
The teleportation and quantum information splitting fidelities associated with
the GHZ and W_A resource states of the excitonic qubit channels of the FMO
complex show that revivals in fidelities increase with the degree of
non-Markovian strength of the decoherent environment. Results indicate that
quantum information processing tasks involving teleportation followed by the
decodification process involving W_A states of the FMO complex, may play a
critical role during coherent oscillations at physiological temperatures.Comment: 16 pages, new figs, typo
Universal Equation for Efimov States
Efimov states are a sequence of shallow 3-body bound states that arise when
the 2-body scattering length is large. Efimov showed that the binding energies
of these states can be calculated in terms of the scattering length and a
3-body parameter by solving a transcendental equation involving a universal
function of one variable. We calculate this universal function using effective
field theory and use it to describe the three-body system of 4He atoms. We also
extend Efimov's theory to include the effects of deep 2-body bound states,
which give widths to the Efimov states.Comment: 8 pages, revtex4, 2 ps figures, table with numerical values of
universal function adde
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