13,084 research outputs found
Coherent Production of Pairs of Parabosons of Order 2
A parameter-free statistical model is used to study multiplicity signatures
for coherent production of charged-pairs of parabosons of order p=2 in
comparison with those arising in the case of ordinary bosons, p=1. Two
non-negative real parameters arise because "ab" and "ba" are fundamentally
distinct pair operators of charge "+1", A-quanta and charge "-1", B-quanta
parabosons. In 3D plots of P(q)_m = "The probability of m paraboson
charged-pairs and q positive parabosons" versus and , the p=1
curve is found to lie on the relatively narrow 2D p=2 surface.Comment: 25 pages, 16 figures, no macro
Structural and electronic properties of the graphene/Al/Ni(111) intercalation-like system
Decoupling of the graphene layer from the ferromagnetic substrate via
intercalation of sp metal has recently been proposed as an effective way to
realize single-layer graphene-based spin-filter. Here, the structural and
electronic properties of the prototype system, graphene/Al/Ni(111), are
investigated via combination of electron diffraction and spectroscopic methods.
These studies are accompanied by state-of-the-art electronic structure
calculations. The properties of this prospective Al-intercalation-like system
and its possible implementations in future graphene-based devices are
discussed.Comment: 20 pages, 8 figures, and supplementary materia
Discrimination between evolution operators
Under broad conditions, evolutions due to two different Hamiltonians are
shown to lead at some moment to orthogonal states. For two spin-1/2 systems
subject to precession by different magnetic fields the achievement of
orthogonalization is demonstrated for every scenario but a special one. This
discrimination between evolutions is experimentally much simpler than
procedures proposed earlier based on either sequential or parallel application
of the unknown unitaries. A lower bound for the orthogonalization time is
proposed in terms of the properties of the two Hamiltonians.Comment: 7 pages, 2 figures, REVTe
On the efficiency of Hamiltonian-based quantum computation for low-rank matrices
We present an extension of Adiabatic Quantum Computing (AQC) algorithm for
the unstructured search to the case when the number of marked items is unknown.
The algorithm maintains the optimal Grover speedup and includes a small
counting subroutine.
Our other results include a lower bound on the amount of time needed to
perform a general Hamiltonian-based quantum search, a lower bound on the
evolution time needed to perform a search that is valid in the presence of
control error and a generic upper bound on the minimum eigenvalue gap for
evolutions.
In particular, we demonstrate that quantum speedup for the unstructured
search using AQC type algorithms may only be achieved under very rigid control
precision requirements.Comment: 17 pages, no figures, to appear in JM
Graphene on ferromagnetic surfaces and its functionalization with water and ammonia
Here we present an angle-resolved photoelectron spectroscopy (ARPES), x-ray
absorption spec-troscopy (XAS), and density-functional theory (DFT)
investigations of water and ammonia ad-sorption on graphene/Ni(111). Our
results on graphene/Ni(111) reveal the existence of interface states,
originating from the strong hybridization of the graphene {\pi} and
spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O
(NH3)/graphene/Ni(111) system give an information about the kind of interaction
between adsorbed molecules and graphene on Ni(111). The presented experimental
data are compared with the results obtained in the framework of the DFT
approach.Comment: accepted in Nanoscale Research Letters; 16 pages, 4 figures, 2 table
Quantum quenches of ion Coulomb crystals across structural instabilities
Quenches in an ion chain can create coherent superpositions of motional
states across the linear-zigzag structural transition. The procedure has been
described in [Phys. Rev. A 84, 063821 (2011)] and makes use of spin-dependent
forces, so that a coherent superposition of the electronic states of one ion
evolves into an entangled state between the chain's internal and external
degrees of freedom. The properties of the crystalline state so generated are
theoretically studied by means of Ramsey interferometry on one ion of the
chain. An analytical expression for the visibility of the interferometric
measurement is obtained for a chain of arbitrary number of ions and as a
function of the time elapsed after the quench. Sufficiently close to the
linear-zigzag instability the visibility decays very fast, but exhibits
revivals at the period of oscillation of the mode that drives the structural
instability. These revivals have a periodicity that is independent of the
crystal size, and they signal the creation of entanglement by the quantum
quench.Comment: 14 pages, 8 figures; added a paragraph in the introduction providing
more background, added paragraph at the end of Sec. IV discussing
experimental parameter
Experimental and Numerical Characterization of Transient Insertion of Heat Flux Gages in a Cylindrical Black Body Cavity at 1100 C
Initial transient thermal models have been developed to simulate a heat flux gage calibration process capable of generating high heat flux levels of interest to reciprocating and gas turbine engine industries as well as the aerospace industry. These transient models are based on existing, experimentally validated, steady state models of the cylindrical blackbody calibration system. The steady state models were modified to include insertion of a heat flux gage into the hot zone of the calibration system and time varying electrical current passing through the resistance heated blackbody. Heat fluxes computed using the initial transient models were compared to experimental measurements. The calculated and measured transient heat fluxes were within 5% indicating that the major physical phenomena in the transient calibration had been captured by the models. The predicted and measured transient heat fluxes were also compared at two different gage insertion depths. These results indicated that there is an optimum insertion position which maximizes heat flux and minimizes cavity disturbance
Extraction efficiency of drifting electrons in a two-phase xenon time projection chamber
We present a measurement of the extraction efficiency of quasi-free electrons
from the liquid into the gas phase in a two-phase xenon time-projection
chamber. The measurements span a range of electric fields from 2.4 to 7.1 kV/cm
in the liquid xenon, corresponding to 4.5 to 13.1 kV/cm in the gaseous xenon.
Extraction efficiency continues to increase at the highest extraction fields,
implying that additional charge signal may be attained in two-phase xenon
detectors through careful high-voltage engineering of the gate-anode region
Is Weak Pseudo-Hermiticity Weaker than Pseudo-Hermiticity?
For a weakly pseudo-Hermitian linear operator, we give a spectral condition
that ensures its pseudo-Hermiticity. This condition is always satisfied
whenever the operator acts in a finite-dimensional Hilbert space. Hence weak
pseudo-Hermiticity and pseudo-Hermiticity are equivalent in finite-dimensions.
This equivalence extends to a much larger class of operators. Quantum systems
whose Hamiltonian is selected from among these operators correspond to
pseudo-Hermitian quantum systems possessing certain symmetries.Comment: published version, 10 page
Probing the outer vestibule of a sodium channel voltage sensor
The second and third basic residues of the S4 segment of domain 4 (D4:R2 and D4:R3) of the human skeletal muscle Na+ channel are known to be translocated from a cytoplasmic to an extracellular position during depolarization. Accessibilities of individual S4 residues were assayed by alteration of inactivation kinetics during modification of cysteine mutants by hydrophilic methanethiosulfonate reagents. The voltage dependences of the reaction rates are identical for extracellular application of cationic methanethiosulfonate-ethyltrimethylammonium (MTSET) and anionic methanethiosulfonate-ethylsulfonate (MTSES), suggesting that D4:R3C is situated outside the membrane electric field at depolarized voltages. The absolute rate of R3C modification is 281-fold greater for MTSET than for MTSES, however, suggesting that at depolarized voltages this S4 thiol resides in a negatively charged hydrophilic crevice. The two hydrophobic residues between D4:R2C and D4:R3C in the primary sequence (L1452 and A1453) are not externally exposed at any voltage. An alpha-helical representation of D4/S4 shows that the basic residues D4:R2 and D4:R3 are on the face opposite that of L1452 and A1453. We propose that in the depolarized conformation, the hydrophobic face of this portion of D4/S4 remains in contact with a hydrophobic region of the extracellular vestibule of the S4 channel
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