3,684 research outputs found
Optimal Quantum State Estimation with Use of the No-Signaling Principle
A simple derivation of the optimal state estimation of a quantum bit was
obtained by using the no-signaling principle. In particular, the no-signaling
principle determines a unique form of the guessing probability independently of
figures of merit, such as the fidelity or information gain. This proves that
the optimal estimation for a quantum bit can be achieved by the same
measurement for almost all figures of merit.Comment: 3 pages, 1 figur
Quantum State Discrimination with General Figures of Merit
We solve the problem of quantum state discrimination with "general
(symmetric) figures of merit" for an even number of symmetric quantum bits with
use of the no-signaling principle. It turns out that conditional probability
has the same form for any figure of merit. Optimal measurement and
corresponding conditional probability are the same for any monotonous figure of
merit.Comment: 5 pages, 2 figure
Role of hydrogen carrier gas on the growth of few layer hexagonal boron nitrides by metal-organic chemical vapor deposition
1140Ysciescopu
Quasi-Free-Standing Graphene Monolayer on a Ni Crystal through Spontaneous Na Intercalation
Graphene on metal substrates often shows different electronic properties from isolated graphene because of graphene-substrate interactions. One needs to remove the metals with acids and then to transfer graphene to weakly interacting substrates to recover electrical properties inherent in graphene. This process is not easy and besides causes undesirable tears, defects, and impurities in graphene. Here, we report a method to recover the electronic structure of graphene from a strongly interacting Ni substrate by spontaneous Na intercalation. In order to characterize the intercalation process, the density-functional-theory calculations and angle-resolved photoemission-spectroscopy (ARPES) and scanning-tunneling-microscopy (STM) measurements are carried out. From the density-functional-theory calculations, Na atoms energetically prefer interface intercalation to surface adsorption for the graphene/Ni(111) surface. Unlike most intercalants, Na atoms intercalate spontaneously at room temperature due to a tiny diffusion barrier, which is consistent with our temperature-dependent ARPES and core-level photoemission spectroscopy, and with our submonolayer ARPES and STM results at room temperature. As a result of the spontaneous intercalation, the electronic structure of graphene is almost recovered, as confirmed by the Dirac cone with a negligible band gap in ARPES and the sixfold symmetry in STM.open
The no-boundary measure in string theory: Applications to moduli stabilization, flux compactification, and cosmic landscape
We investigate the no-boundary measure in the context of moduli
stabilization. To this end, we first show that for exponential potentials,
there are no classical histories once the slope exceeds a critical value. We
also investigate the probability distributions given by the no-boundary wave
function near maxima of the potential. These results are then applied to a
simple model that compactifies 6D to 4D (HBSV model) with fluxes. We find that
the no-boundary wave function effectively stabilizes the moduli of the model.
Moreover, we find the a priori probability for the cosmological constant in
this model. We find that a negative value is preferred, and a vanishing
cosmological constant is not distinguished by the probability measure. We also
discuss the application to the cosmic landscape. Our preliminary arguments
indicate that the probability of obtaining anti de Sitter space is vastly
greater than for de Sitter.Comment: 27 pages, 8 figure
Annealing temperature dependence of capacitance-voltage characteristics in Ge-nanocrystal-based nonvolatile memory structures
The annealing temperature (TA) dependence of capacitance-voltage (C-V) characteristics has been studied in metal-oxide-semiconductor structures containing Ge nanocrystals (NCs) produced by ion implantation and annealing. These structures are of interest for application as nonvolatile memory and TA is shown to have a strong influence on the C-V hysteresis. This behavior is shown to be correlated with structural changes of the Ge NCs which have been characterized by synchrotron-radiation photoemission spectroscopy. Specifically, well-defined C-V characteristics with large hysteresis were found only for annealing temperatures greater than 950 °C where Ge nanocrystals are known to form. In this temperature regime, transmission electron microcopy and energy dispersive x-ray spectroscopy demonstrate the existence of regularly arranged Ge NCs of approximately 3–5 nm diameter located around 6.7 nm from the interface
No-signaling Principle Can Determine Optimal Quantum State Discrimination
We provide a general framework of utilizing the no-signaling principle in
derivation of the guessing probability in the minimum-error quantum state
discrimination. We show that, remarkably, the guessing probability can be
determined by the no-signaling principle. This is shown by proving that in the
semidefinite programming for the discrimination, the optimality condition
corresponds to the constraint that quantum theory cannot be used for a
superluminal communication. Finally, a general bound to the guessing
probability is presented in a closed form.Comment: 4 page
The causal structure of dynamical charged black holes
We study the causal structure of dynamical charged black holes, with a
sufficient number of massless fields, using numerical simulations. Neglecting
Hawking radiation, the inner horizon is a null Cauchy horizon and a curvature
singularity due to mass inflation. When we include Hawking radiation, the inner
horizon becomes space-like and is separated from the Cauchy horizon, which is
parallel to the out-going null direction. Since a charged black hole must
eventually transit to a neutral black hole, we studied the neutralization of
the black hole and observed that the inner horizon evolves into a space-like
singularity, generating a Cauchy horizon which is parallel to the in-going null
direction. Since the mass function is finite around the inner horizon, the
inner horizon is regular and penetrable in a general relativistic sense.
However, since the curvature functions become trans-Planckian, we cannot
saymore about the region beyond the inner horizon, and it is natural to say
that there is a 'physical' space-like singularity. However, if we assume an
exponentially large number of massless scalar fields, our results can be
extended beyond the inner horizon. In this case, strong cosmic censorship and
black hole complementarity can be violated.Comment: 23 pages, 23 figure
Dynamical formation and evolution of (2+1)-dimensional charged black holes
In this paper, we investigate the dynamical formation and evolution of 2 +
1-dimensional charged black holes. We numerically study dynamical collapses of
charged matter fields in an anti de Sitter background and note the formation of
black holes using the double-null formalism. Moreover, we include re-normalized
energy-momentum tensors assuming the S-wave approximation to determine
thermodynamical back-reactions to the internal structures. If there is no
semi-classical effects, the amount of charge determines the causal structures.
If the charge is sufficiently small, the causal structure has a space-like
singularity. However, as the charge increases, an inner Cauchy horizon appears.
If we have sufficient charge, we see a space-like outer horizon and a time-like
inner horizon, and if we give excessive charge, black hole horizons disappear.
We have some circumstantial evidences that weak cosmic censorship is still
satisfied, even for such excessive charge cases. Also, we confirm that there is
mass inflation along the inner horizon, although the properties are quite
different from those of four-dimensional cases. Semi-classical back-reactions
will not affect the outer horizon, but they will affect the inner horizon. Near
the center, there is a place where negative energy is concentrated. Thus,
charged black holes in three dimensions have two types of curvature
singularities in general: via mass inflation and via a concentration of
negative energy. Finally, we classify possible causal structures.Comment: 40 pages, 15 figure
How to Device-Independently Generate States for Which Unambiguous State Discrimination is Impossible
We describe how to device-independently generate a set of quantum states for
which unambiguous state discrimination is not possible. First, we derive a
formula that a certain non-signaling black box must satisfy. Then, we describe
how to generate a set of quantum states. Devices for generating states and
possible measurements on the states can be put into a black box. Because this
black box is non-signaling, it satisfies the formula. Using the formula, we
prove that unambiguous state discrimination is not possible for the generated
states. Because we did not consider internal mechanisms but only outcomes, our
argument is valid for any (imperfect) devices.Comment: Published version, no essential correction, 3 page
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