156 research outputs found
Modal quantum theory
We present a discrete model theory similar in structure to ordinary quantum
mechanics, but based on a finite field instead of complex amplitudes. The
interpretation of this theory involves only the "modal" concepts of possibility
and necessity rather than quantitative probability measures. Despite its
simplicity, our model theory includes entangled states and has versions of both
Bell's theorem and the no cloning theorem.Comment: Presented at the 7th Workshop on Quantum Physics and Logic, Oxford
University (29-30 May 2010). Revised 1 Aug 2011 in response to referee
comment
Enhancement of nonclassical properties of two qubits via deformed operators
We explore the dynamics of two atoms interacting with a cavity field via
deformed operators. Properties of the asymptotic regularization of entanglement
measures proving, for example, purity cost, regularized fidelity and accuracy
of information transfer are analyzed. We show that the robustness of a
bipartite system having a finite number of quantum states vanishes at finite
photon numbers, for arbitrary interactions between its constituents and with
cavity field. Finally it is shown that the stability of the purity and the
fidelity is improved in the absence of the deformation parameters
Effects and Propositions
The quantum logical and quantum information-theoretic traditions have exerted
an especially powerful influence on Bub's thinking about the conceptual
foundations of quantum mechanics. This paper discusses both the quantum logical
and information-theoretic traditions from the point of view of their
representational frameworks. I argue that it is at this level, at the level of
its framework, that the quantum logical tradition has retained its centrality
to Bub's thought. It is further argued that there is implicit in the quantum
information-theoretic tradition a set of ideas that mark a genuinely new
alternative to the framework of quantum logic. These ideas are of considerable
interest for the philosophy of quantum mechanics, a claim which I defend with
an extended discussion of their application to our understanding of the
philosophical significance of the no hidden variable theorem of Kochen and
Specker.Comment: Presented to the 2007 conference, New Directions in the Foundations
of Physic
Inelastic electron transport in granular arrays
Transport properties of granular systems are governed by Coulomb blockade
effects caused by the discreteness of the electron charge. We show that, in the
limit of vanishing mean level spacing on the grains, the low-temperature
behavior of 1d and 2d arrays is insulating at any inter-grain coupling
(characterized by a dimensionless conductance g.) In 2d and g>>1, there is a
sharp Berezinskii-Kosterlitz-Thouless crossover to the conducting phase at a
certain temperature, T_{BKT}. These results are obtained by applying an
instanton analysis to map the conventional `phase' description of granular
arrays onto the dual `charge' representation.Comment: 24 pages, 8 figure
Classical Vs Quantum Probability in Sequential Measurements
We demonstrate in this paper that the probabilities for sequential
measurements have features very different from those of single-time
measurements. First, they cannot be modelled by a classical stochastic process.
Second, they are contextual, namely they depend strongly on the specific
measurement scheme through which they are determined. We construct
Positive-Operator-Valued measures (POVM) that provide such probabilities. For
observables with continuous spectrum, the constructed POVMs depend strongly on
the resolution of the measurement device, a conclusion that persists even if we
consider a quantum mechanical measurement device or the presence of an
environment. We then examine the same issues in alternative interpretations of
quantum theory. We first show that multi-time probabilities cannot be naturally
defined in terms of a frequency operator. We next prove that local hidden
variable theories cannot reproduce the predictions of quantum theory for
sequential measurements, even when the degrees of freedom of the measuring
apparatus are taken into account. Bohmian mechanics, however, does not fall in
this category. We finally examine an alternative proposal that sequential
measurements can be modelled by a process that does not satisfy the Kolmogorov
axioms of probability. This removes contextuality without introducing
non-locality, but implies that the empirical probabilities cannot be always
defined (the event frequencies do not converge). We argue that the predictions
of this hypothesis are not ruled out by existing experimental results
(examining in particular the "which way" experiments); they are, however,
distinguishable in principle.Comment: 56 pages, latex; revised and restructured. Version to appear in
Found. Phy
Physical Characterization of an Unlensed, Dusty Star-forming Galaxy at z = 5.85
We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 \ub1 0.001. This is the highest-redshift unlensed DSFG (and fourth most distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 \u3bcm to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z > 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6\u21925) and p-H2O (21,1 \u2192 20,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M o\u2d9 yr-1 and 220 M o\u2d9 yr-1, total molecular hydrogen gas mass of (1.7 \ub1 0.4)
7 1011 M o\u2d9, dust mass of (1.3 \ub1 0.3)
7 109 M o\u2d9, and stellar mass of (3.2-1.5+1.0)
7 109 M o\u2d9. The total halo mass, (3.3 \ub1 0.8)
7 1012 M o\u2d9, is predicted to exceed 1015 M o\u2d9 by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in \u3c4 depl = 40-80 Myr, converting its large molecular gas reservoir (gas fraction of 96-2+1) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z \u2a86 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times ( 721 Gyr)
Nonlinear model for disordered superconductors
We suggest a novel nonlinear -model for the description of disordered
superconductors. The main distinction from existing models lies in the fact
that the saddle point equation is solved non-perturbatively in the
superconducting pairing field. It allows one to use the model both in the
vicinity of the metal-superconductor transition and well below its critical
temperature with full account for the self-consistency conditions. We show that
the model reproduces a set of known results in different limiting cases, and
apply it for a self-consistent description of the proximity effect at the
superconductor-metal interface.Comment: Revised version, 8 pages, 1 fig., revtex; final version, as
published, contains a few corrections in the summar
The VANDELS ESO public spectroscopic survey
VANDELS is a uniquely deep spectroscopic survey of high-redshift galaxies with the VIMOS spectrograph on ESO’s Very Large Telescope (VLT). The survey has obtained ultradeep optical (0.48 < λ < 1.0 μ m) spectroscopy of ≃2100 galaxies within the redshift interval 1.0 ≤ z ≤ 7.0, over a total area of ≃0.2 deg2 centred on the CANDELS Ultra Deep Survey and Chandra Deep Field South fields. Based on accurate photometric redshift pre-selection, 85 per cent of the galaxies targeted by VANDELS were selected to be at z ≥ 3. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the fundamental aim of the survey is to provide the high-signal-to-noise ratio spectra necessary to measure key physical properties such as stellar population ages, masses, metallicities, and outflow velocities from detailed absorption-line studies. Using integration times calculated to produce an approximately constant signal-to-noise ratio (20 < tint< 80 h), the VANDELS survey targeted: (a) bright star-forming galaxies at 2.4 ≤ z ≤ 5.5, (b) massive quiescent galaxies at 1.0 ≤ z ≤ 2.5, (c) fainter star-forming galaxies at 3.0 ≤ z ≤ 7.0, and (d) X-ray/Spitzer-selected active galactic nuclei and Herschel-detected galaxies. By targeting two extragalactic survey fields with superb multiwavelength imaging data, VANDELS will produce a unique legacy data set for exploring the physics underpinning high-redshift galaxy evolution. In this paper, we provide an overview of the VANDELS survey designed to support the science exploitation of the first ESO public data release, focusing on the scientific motivation, survey design, and target selection
Chelation in Metal Intoxication
Chelation therapy is the preferred medical treatment for reducing the toxic effects of metals. Chelating agents are capable of binding to toxic metal ions to form complex structures which are easily excreted from the body removing them from intracellular or extracellular spaces. 2,3-Dimercaprol has long been the mainstay of chelation therapy for lead or arsenic poisoning, however its serious side effects have led researchers to develop less toxic analogues. Hydrophilic chelators like meso-2,3-dimercaptosuccinic acid effectively promote renal metal excretion, but their ability to access intracellular metals is weak. Newer strategies to address these drawbacks like combination therapy (use of structurally different chelating agents) or co-administration of antioxidants have been reported recently. In this review we provide an update of the existing chelating agents and the various strategies available for the treatment of heavy metals and metalloid intoxications
- …