292 research outputs found
Two-photon coincident-frequency-entanglement via extended phase matching
We demonstrate a new class of frequency-entangled states generated via
spontaneous parametric down-conversion under extended phase matching
conditions. Biphoton entanglement with coincident signal and idler frequencies
is observed over a broad bandwidth in periodically poled KTiOPO. We
demonstrate high visibility in Hong-Ou-Mandel interferometric measurements
under pulsed pumping without spectral filtering, which indicates excellent
frequency indistinguishability between the down-converted photons. The
coincident-frequency entanglement source is useful for quantum information
processing and quantum measurement applications.Comment: 4 pages, 3 figures, submitted to PR
Toward fabrication of devices based on graphene/oxide multilayers
Owing to its high electrical conductivity, low density, and flexibility, graphene has great potential for use as a building block in a wide range of applications from nanoelectronics to biosensing and high-frequency devices. For many device applications, it is required to deposit dielectric materials on graphene at high temperatures and in ambient oxygen. This has been proven to be highly challenging because these conditions cause significant degradation in graphene. In this work, we investigate the degradation of graphene at elevated temperatures in an oxygen atmosphere and possible protection mechanisms to enable the growth of oxide thin films on graphene at higher temperatures. We show that coating graphene with self-assembled monolayers of hexamethyldisilazane (HMDS) prior to a high-temperature deposition can significantly reduce the damage induced. Furthermore, a graphene sample treated with HMDS displayed a weaker doping effect due to weak interaction with oxygen species than bare graphene, and a much slower rate of electrical resistance degradation was exhibited during annealing. Thus, it is a promising approach that could enable the deposition of metal oxide materials on graphene at high temperatures without significant degradation in graphene quality, which is critical for a wide range of applications
Multiphase strontium molybdate thin films for plasmonic local heating applications
In the search for alternative plasmonic materials SrMoO3 has recently been identified as possessing a number of desirable optical properties. Owing to the requirement for many plasmonic devices to operate at elevated temperatures however, it is essential to characterize the degradation of these properties upon heating. Here, SrMoO3 thin films are annealed in air at temperatures ranging from 75 - 500{\deg} C. Characterizations by AFM, XRD, and spectroscopic ellipsometry after each anneal identify a loss of metallic behaviour after annealing at 500{\deg} C, together with the underlying mechanism. Moreover, it is shown that by annealing the films in nitrogen following deposition, an additional crystalline phase of SrMoO4 is induced at the film surface, which suppresses oxidation at elevated temperatures
Complementarity, quantum erasure and delayed choice with modified Mach-Zehnder interferometers
Often cited dictums in Quantum Mechanics include "observation disturbance
causes loss of interference" and "ignorance is interference". In this paper we
propose and describe a series of experiments with modified Mach-Zehnder
interferometers showing that one has to be careful when applying such dictums.
We are able to show that without interacting in any way with the light quantum
(or quanta) expected to behave "wave-like", interference fringes can be lost by
simply gaining (or having the potential to gain) the which-path knowledge.
Erasing this information may revive the interference fringes. Delayed choice
can be added, arriving to an experiment in line with Wheeler's original
proposal. We also show that ignorance is not always synonym with having the
interference fringes. The often-invoked "collapse of the wavefunction" is found
to be a non-necessary ingredient to describe our experiments.Comment: 8 pages, 3 figures; to appear in EPJ
Entanglement and visibility at the output of a Mach-Zehnder interferometer
We study the entanglement between the two beams exiting a Mach-Zehnder
interferometer fed by a couple of squeezed-coherent states with arbitrary
squeezing parameter. The quantum correlations at the output are function of the
internal phase-shift of the interferometer, with the output state ranging from
a totally disentangled state to a state whose degree of entanglement is an
increasing function of the input squeezing parameter. A couple of squeezed
vacuum at the input leads to maximum entangled state at the output. The fringes
visibilities resulting from measuring the coincidence counting rate or the
squared difference photocurrent are evaluated and compared each other.
Homodyne-like detection turns out to be preferable in almost all situations,
with the exception of the very low signals regime.Comment: 6 figs, accepted for publication on PRA, see also
http://enterprise.pv.infn.it/~pari
Parsimonious test of dynamic interaction
In recent years, there have been significant advances in the technology used to collect data on the movement and activity patterns of humans and animals. GPS units, which form the primary source of location data, have become cheaper, more accurate, lighter and less powerâhungry, and their accuracy has been further improved with the addition of inertial measurement units. The consequence is a glut of geospatial time series data, recorded at rates that range from one position fix every several hours (to maximize system lifetime) to ten fixes per second (in high dynamic situations). Since data of this quality and volume have only recently become available, the analytical methods to extract behavioral information from raw position data are at an early stage of development. An instance of this lies in the analysis of animal movement patterns. When investigating solitary animals, the timing and location of instances of avoidance and association are important behavioral markers. In this paper, a novel analytical method to detect avoidance and association between individuals is proposed; unlike existing methods, assumptions about the shape of the territories or the nature of individual movement are not needed. Simulations demonstrate that false positives (type I error) are rare (1%â3%), which means that the test rarely suggests that there is an association if there is none
Quantum Logic Operations Using Single Photons and the Zeno Effect
We show that the quantum Zeno effect can be used to implement several quantum
logic gates for photonic qubits, including a gate that is similar to the
square-root of SWAP operation. The operation of these devices depends on the
fact that photons can behave as if they were non-interacting fermions instead
of bosons in the presence of a strong Zeno effect. These results are discussed
within the context of several no-go theorems for non-interacting fermions or
bosons.Comment: 15 pages, 4 figure
Unique metabolites protect earthworms against plant polyphenols
All higher plants produce polyphenols, for defence against above-ground herbivory. These polyphenols also influence the soil micro- and macro-fauna that break down plant leaf litter. Polyphenols therefore indirectly affect the fluxes of soil nutrients and, ultimately, carbon turnover and ecosystem functioning in soils. It is unknown how earthworms, the major component of animal biomass in many soils, cope with high-polyphenol diets. Here, we show that earthworms possess a class of unique surface-active metabolites in their gut, which we term âdrilodefensinsâ. These compounds counteract the inhibitory effects of polyphenols on earthworm gut enzymes, and high-polyphenol diets increase drilodefensin concentrations in both laboratory and field populations. This shows that drilodefensins protect earthworms from the harmful effects of ingested polyphenols. We have identified the key mechanism for adaptation to a dietary challenge in an animal group that has a major role in organic matter recycling in soils worldwide
Detection of first-order liquid/liquid phase transitions in yttrium oxide-aluminium oxide melts
We combine small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) with aerodynamic levitation techniques to study in situ phase transitions in the liquid state under contactless conditions. At very high temperatures, yttria-alumina melts show a first-order transition, previously inferred from phase separation in quenched glasses. We show how the transition coincides with a narrow and reversible maximum in SAXS indicative of liquid unmixing on the nanoscale, combined with an abrupt realignment in WAXS features related to reversible shifts in polyhedral packing on the atomic scale. We also observed a rotary action in the suspended supercooled drop driven by repetitive transitions (a polyamorphic rotor) from which the reversible changes in molar volume (1.2 ± 0.2 cubic centimeters) and entropy (19 ± 4 joules moleâ1 kelvinâ1) can be estimated
Quantum Teleportation and Bell's Inequality Using Single-Particle Entanglement
A single-particle entangled state can be generated by illuminating a beam
splitter with a single photon. Quantum teleportation utilizing such a
single-particle entangled state can be successfully achieved with a simple
setup consisting only of linear optical devices such as beam splitters and
phase shifters. Application of the locality assumption to a single-particle
entangled state leads to Bell's inequality, a violation of which signifies the
nonlocal nature of a single particle.Comment: 7 pages including 3 figures in eps-forma
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