304 research outputs found
Two proposals for testing quantum contextuality of continuous-variable states
We investigate the violation of non-contextuality by a class of continuous
variable states, including variations of entangled coherent states (ECS's) and
a two-mode continuous superposition of coherent states. We generalise the
Kochen-Specker (KS) inequality discussed in A. Cabello, Phys. Rev. Lett. {\bf
101}, 210401 (2008) by using effective bidimensional observables implemented
through physical operations acting on continuous variable states, in a way
similar to an approach to the falsification of Bell-CHSH inequalities put
forward recently. We test for state-independent violation of KS inequalities
under variable degrees of state entanglement and mixedness. We then demonstrate
theoretically the violation of a KS inequality for any two-mode state by using
pseudo-spin observables and a generalized quasi-probability function.Comment: 7 pages, 2 figures, RevTeX
Keck Interferometer autoaligner: algorithms and techniques
The Keck Interferometer includes an autoalignment system consisting of pop-up targets located at strategic locations along the beam trains of each arm of the instrument along with a sensor and control system. We briefly describe the hardware of the system and then proceed to a description of the two operational modes of the system. These are: 1) to provide an initial alignment of the coude paths in each arm, and 2) to recover coude alignments between changes of the static delay sled positions. For the initial alignment mode, we review the system performance requirements along with the software used for image acquisition and centroiding. For coudé alignment recovery, we describe beam-train surveys through the static delay (Long Delay Line) and criteria for a successful recovery of a coudé alignment. Finally, we describe the results of testing of the autoalignment system
Duality between a deterministic cellular automaton and a bosonic quantum field theory in 1+1 dimensions
Methods developed in a previous paper are employed to define an exact
correspondence between the states of a deterministic cellular automaton in 1+1
dimensions and those of a bosonic quantum field theory. The result may be used
to argue that quantum field theories may be much closer related to
deterministic automata than what is usually thought possible. Version 2 had a
minor typo corrected and notation was made more consistent.Comment: 18 pages (incl. Title page). No figure
Entanglement of two-mode Bose-Einstein condensates
We investigate the entaglement characteristics of two general bimodal
Bose-Einstein condensates - a pair of tunnel-coupled Bose-Einstein condensates
and the atom-molecule Bose-Einstein condensate. We argue that the entanglement
is only physically meaningful if the system is viewed as a bipartite system,
where the subsystems are the two modes. The indistinguishibility of the
particles in the condensate means that the atomic constituents are physically
inaccessible and thus the degree of entanglement between individual particles,
unlike the entanglement between the modes, is not experimentally relevant so
long as the particles remain in the condensed state. We calculate the
entanglement between the modes for the exact ground state of the two bimodal
condensates and consider the dynamics of the entanglement in the tunnel-coupled
case.Comment: 11 pages, 8 figures, submitted to Physical Review A, to be presented
at the third UQ Mathematical Physics workshop, Oct. 4-6; changes made in
response to referee comment
Quantum Gravity as a Dissipative Deterministic System
It is argued that the so-called holographic principle will obstruct attempts
to produce physically realistic models for the unification of general
relativity with quantum mechanics, unless determinism in the latter is
restored. The notion of time in GR is so different from the usual one in
elementary particle physics that we believe that certain versions of hidden
variable theories can -- and must -- be revived. A completely natural procedure
is proposed, in which the dissipation of information plays an essential role.
Unlike earlier attempts, it allows us to use strictly continuous and
differentiable classical field theories as a starting point (although discrete
variables, leading to fermionic degrees of freedom, are also welcome), and we
show how an effective Hilbert space of quantum states naturally emerges when
one attempts to describe the solutions statistically. Our theory removes some
of the mysteries of the holographic principle; apparently non-local features
are to be expected when the quantum degrees of freedom of the world are
projected onto a lower-dimensional black hole horizon. Various examples and
models illustrate the points we wish to make, notably a model showing that
massless, non interacting neutrinos are deterministic.Comment: 20 pages plain TeX, 2 figures PostScript. Added some further
explanations, and the definitions of `beable' and `changeable'. A minor error
correcte
Galaxy formation in the Planck cosmology - I. Matching the observed evolution of star formation rates, colours and stellar masses
We have updated the Munich galaxy formation model to the Planck first-year cosmology, while modifying the treatment of baryonic processes to reproduce recent data on the abundance and passive fractions of galaxies from z = 3 down to z = 0. Matching these more extensive and more precise observational results requires us to delay the reincorporation of wind ejecta, to lower the surface density threshold for turning cold gas into stars, to eliminate ram-pressure stripping in haloes less massive than ∼1014 M⊙, and to modify our model for radio mode feedback. These changes cure the most obvious failings of our previous models, namely the overly early formation of low-mass galaxies and the overly large fraction of them that are passive at late times. The new model is calibrated to reproduce the observed evolution both of the stellar mass function and of the distribution of star formation rate at each stellar mass. Massive galaxies (log M⋆/M⊙ ≥ 11.0) assemble most of their mass before z = 1 and are predominantly old and passive at z = 0, while lower mass galaxies assemble later and, for log M⋆/M⊙ ≤ 9.5, are still predominantly blue and star forming at z = 0. This phenomenological but physically based model allows the observations to be interpreted in terms of the efficiency of the various processes that control the formation and evolution of galaxies as a function of their stellar mass, gas content, environment and time
Simulations of the galaxy population constrained by observations from z=3 to the present day: implications for galactic winds and the fate of their ejecta
We apply Monte Carlo Markov Chain (MCMC) methods to large-scale simulations of galaxy formation in a LambdaCDM cosmology in order to explore how star formation and feedback are constrained by the observed luminosity and stellar mass functions of galaxies. We build models jointly on the Millennium and Millennium-II simulations, applying fast sampling techniques which allow observed galaxy abundances over the ranges 7<log(M*/Msun)<12 and z=0 to z=3 to be used simultaneously as constraints in the MCMC analysis. When z=0 constraints alone are imposed, we reproduce the results of previous modelling by Guo et al. (2012), but no single set of parameters can reproduce observed galaxy abundances at all redshifts simultaneously, reflecting the fact that low-mass galaxies form too early and thus are overabundant at high redshift in this model. The data require the efficiency with which galactic wind ejecta are reaccreted to vary with redshift and halo mass quite differently than previously assumed, but in a similar way as in some recent hydrodynamic simulations of galaxy formation. We propose a specific model in which reincorporation timescales vary inversely with halo mass and are independent of redshift. This produces an evolving galaxy population which fits observed abundances as a function of stellar mass, B- and K-band luminosity at all redshifts simultaneously. It also produces a significant improvement in two other areas where previous models were deficient. It leads to present day dwarf galaxy populations which are younger, bluer, more strongly star-forming and more weakly clustered on small scales than before, although the passive fraction of faint dwarfs remains too high
The state of the Martian climate
60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes
Keck Interferometer autoaligner: algorithms and techniques
The Keck Interferometer includes an autoalignment system consisting of pop-up targets located at strategic locations along the beam trains of each arm of the instrument along with a sensor and control system. We briefly describe the hardware of the system and then proceed to a description of the two operational modes of the system. These are: 1) to provide an initial alignment of the coude paths in each arm, and 2) to recover coude alignments between changes of the static delay sled positions. For the initial alignment mode, we review the system performance requirements along with the software used for image acquisition and centroiding. For coudé alignment recovery, we describe beam-train surveys through the static delay (Long Delay Line) and criteria for a successful recovery of a coudé alignment. Finally, we describe the results of testing of the autoalignment system
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