4,875 research outputs found
Entangling two distant non-interacting microwave modes
We propose a protocol able to prepare two remote and initially uncorrelated
microwave modes in an entangled stationary state, which is certifiable using
only local optical homodyne measurements. The protocol is an extension of
continuous variable entanglement swapping, and exploits two hybrid
quadripartite opto-electro-mechanical systems in which a nanomechanical
resonator acts as a quantum interface able to entangle optical and microwave
fields. The proposed protocol allows to circumvent the problems associated with
the fragility of microwave photons with respect to thermal noise and may
represent a fundamental tool for the realization of quantum networks connecting
distant solid-state and superconducting qubits, which are typically manipulated
with microwave fields. The certifying measurements on the optical modes
guarantee the success of entanglement swapping without the need of performing
explicit measurements on the distant microwave fields.Comment: 7 pages, 3 figures; to appear in the special issue "Quantum and
Hybrid Mechanical Systems - From Fundamentals to Applications" in Annalen der
Physi
Nanoparticle behaviour in an urban street canyon at different heights and implications on indoor respiratory doses
The amount of outdoor particles that indoor environments receive depends on the particle infiltration factors (Fin), peculiar of each environment, and on the outdoor aerosol concentrations and size distributions. The respiratory doses received, while residing indoor, will change accordingly. This study aims to ascertain to what extent such doses are affected by the vertical distance from the traffic sources. Particle number size distributions have been simultaneously measured at street level and at about 20 m height in a street canyon in downtown Rome. The same Fin have been adopted to estimate indoor aerosol concentrations, due to the infiltration of outdoor particles and then the relevant daily respiratory doses. Aerosol concentrations at ground floor were more than double than at 20 m height and richer in ultrafine particles. Thus, although aerosol infiltration efficiency was on average higher at 20 m height than at ground floor, particles more abundantly infiltrated at ground level. On a daily basis, this involved a 2.5-fold higher dose at ground level than at 20 m height. At both levels, such doses were greater than those estimated over the period of activity of some indoor aerosol sources; therefore, they represent an important contribution to the total daily dose
Dynamic structure factor for 3He in two-dimensions
Recent neutron scattering experiments on 3He films have observed a zero-sound
mode, its dispersion relation and its merging with -and possibly emerging from-
the particle-hole continuum. Here we address the study of the excitations in
the system via quantum Monte Carlo methods: we suggest a practical scheme to
calculate imaginary time correlation functions for moderate-size fermionic
systems. Combined with an efficient method for analytic continuation, this
scheme affords an extremely convincing description of the experimental
findings.Comment: 5 pages, 5 figure
Implementation of the Linear Method for the optimization of Jastrow-Feenberg and Backflow Correlations
We present a fully detailed and highly performing implementation of the
Linear Method [J. Toulouse and C. J. Umrigar (2007)] to optimize
Jastrow-Feenberg and Backflow Correlations in many-body wave-functions, which
are widely used in condensed matter physics. We show that it is possible to
implement such optimization scheme performing analytical derivatives of the
wave-function with respect to the variational parameters achieving the best
possible complexity O(N^3) in the number of particles N.Comment: submitted to the Comp. Phys. Com
Equation of state of two--dimensional He at zero temperature
We have performed a Quantum Monte Carlo study of a two-dimensional bulk
sample of interacting 1/2-spin structureless fermions, a model of He
adsorbed on a variety of preplated graphite substrates. We have computed the
equation of state and the polarization energy using both the standard
fixed-node approximate technique and a formally exact methodology, relying on
bosonic imaginary-time correlation functions of operators suitably chosen in
order to extract fermionic energies. As the density increases, the fixed-node
approximation predicts a transition to an itinerant ferromagnetic fluid,
whereas the unbiased methodology indicates that the paramagnetic fluid is the
stable phase until crystallization takes place. We find that two-dimensional
He at zero temperature crystallizes from the paramagnetic fluid at a
density of 0.061 \AA with a narrow coexistence region of about 0.002
\AA. Remarkably, the spin susceptibility turns out in very good
agreement with experiments.Comment: 7 pages, 7 figure
Imaginary Time Correlations and the phaseless Auxiliary Field Quantum Monte Carlo
The phaseless Auxiliary Field Quantum Monte Carlo method provides a well
established approximation scheme for accurate calculations of ground state
energies of many-fermions systems. Here we apply the method to the calculation
of imaginary time correlation functions. We give a detailed description of the
technique and we test the quality of the results for static and dynamic
properties against exact values for small systems.Comment: 13 pages, 6 figures; submitted to J. Chem. Phy
Local pressure-induced metallization of a semiconducting carbon nanotube in a crossed junction
The electronic and vibrational density of states of a semiconducting carbon
nanotube in a crossed junction was investigated by elastic and inelastic
scanning tunneling spectroscopy. The strong radial compression of the nanotube
at the junction induces local metallization spatially confined to a few nm. The
local electronic modifications are correlated with the observed changes in the
radial breathing and G-band phonon modes, which react very sensitively to local
mechanical deformation. In addition, the experiments reveal the crucial
contribution of the image charges to the contact potential at nanotube-metal
interfaces
A method validation for simultaneous determination of phthalates and bisphenol A released from plastic water containers
Phthalates (or phthalate esters, PAEs) and bisphenol A (BPA) are widely used in various industries, particularly in the fields of cosmetics and packaging, and they increase the malleability and workability of materials. As a result of their use, some international health organizations have begun to study them. In this study, the authors developed a methodology for the simultaneous determination of dimethyl phthalate (DMP), diethyl phthalate (DEP), diisobutyl phthalate (DiBP); dibutyl phthalate (DBP), bis(2-ethylhexyl) phthalate (DEHP); di-n-octyl-phthalate (DnOP) and bisphenol A (BPA) from drinking and non-potable waters. The extraction of PAEs and BPA was performed using a solvent-based dispersive liquid-liquid microextraction (SB-DLLME) method. The analytical determination was performed using a gas chromatography-ion trap mass spectrometry (GC-IT/MS) analysis. The entire procedure was validated as recoveries were studied according to the volume and the extraction solvent used, pH, and ionic strength. Dynamic linearity ranges and linear equations of all the compounds were experimentally determined as well as the limit of detection (LOD) (1-8 ng mL-1) and the limit of quantification (LOQ) (5-14 ng mL-1), reproducibility, and sensitivity. The method was applied to 15 water samples (mineral water and tap water) for determining PAEs and BPA released from the plastic container. After the release simulation, four PAEs (i.e., DiBP, DBP, DHEP, and DnOP) were determined at very low concentrations (below 1.2 ng mL-1) in two water samples from (sport) bottles
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