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Epigenetic Applications in Adverse Outcome Pathways and Chemical Risk Evaluation
Fault-tolerant quantum computation versus Gaussian noise
We study the robustness of a fault-tolerant quantum computer subject to
Gaussian non-Markovian quantum noise, and we show that scalable quantum
computation is possible if the noise power spectrum satisfies an appropriate
"threshold condition." Our condition is less sensitive to very-high-frequency
noise than previously derived threshold conditions for non-Markovian noise.Comment: 30 pages, 6 figure
Entanglement Sharing and Decoherence in the Spin-Bath
The monogamous nature of entanglement has been illustrated by the derivation
of entanglement sharing inequalities - bounds on the amount of entanglement
that can be shared amongst the various parts of a multipartite system.
Motivated by recent studies of decoherence, we demonstrate an interesting
manifestation of this phenomena that arises in system-environment models where
there exists interactions between the modes or subsystems of the environment.
We investigate this phenomena in the spin-bath environment, constructing an
entanglement sharing inequality bounding the entanglement between a central
spin and the environment in terms of the pairwise entanglement between
individual bath spins. The relation of this result to decoherence will be
illustrated using simplified system-bath models of decoherence.Comment: 5 pages, 1 figure v2: 6 pages 2 figures, additional example and
reference
Are There Any Type 2 QSOs? The Case of AXJ0341.4-4453
The X-ray source AXJ0341.4-4453 was described by Boyle et al. as a Type 2 AGN
at z = 0.672 based on the absence of broad emission lines in the observed
wavelength range 4000-7000 Angstroms. We obtained a new spectrum of
AXJ0341.4-4453 extending to 9600 Angstroms which reveals broad Balmer lines and
other characteristics of Seyfert 1 galaxies. The FWHM of broad H-beta is at
least 1600 km/s, while [O III]5007 has FWHM = 730 km/s. The flux ratio [O
III]5007/H-beta = 1. Thus, AXJ0341.4-4453 is by definition a narrow-line
Seyfert 1 galaxy, or perhaps a moderately reddened Seyfert 1 galaxy, but it is
not a Type 2 QSO. Although examples of the latter have long been sought,
particularly in connection with the problem of the X-ray background, there is
still virtually no evidence for the existence of any Type 2 QSO among X-ray
selected samples.Comment: 4 pages, 3 figures, to appear in MNRA
Quantum Walks, Quantum Gates and Quantum Computers
The physics of quantum walks on graphs is formulated in Hamiltonian language,
both for simple quantum walks and for composite walks, where extra discrete
degrees of freedom live at each node of the graph. It is shown how to map
between quantum walk Hamiltonians and Hamiltonians for qubit systems and
quantum circuits; this is done for both a single- and multi-excitation coding,
and for more general mappings. Specific examples of spin chains, as well as
static and dynamic systems of qubits, are mapped to quantum walks, and walks on
hyperlattices and hypercubes are mapped to various gate systems. We also show
how to map a quantum circuit performing the quantum Fourier transform, the key
element of Shor's algorithm, to a quantum walk system doing the same. The
results herein are an essential preliminary to a Hamiltonian formulation of
quantum walks in which coupling to a dynamic quantum environment is included.Comment: 17 pages, 10 figure
Dust in the wind: Crystalline silicates, corundum and periclase in PG 2112+059
We have determined the mineralogical composition of dust in the Broad
Absorption Line (BAL) quasar PG 2112+059 using mid-infrared spectroscopy
obtained with the Spitzer Space Telescope. From spectral fitting of the solid
state features, we find evidence for Mg-rich amorphous silicates with olivine
stoichiometry, as well as the first detection of corundum (Al_2O_3) and
periclase (MgO) in quasars. This mixed composition provides the first direct
evidence for a clumpy density structure of the grain forming region. The
silicates in total encompass 56.5% of the identified dust mass, while corundum
takes up 38 wt.%. Depending on the choice of continuum, a range of mass
fractions is observed for periclase ranging from 2.7% in the most conservative
case to 9% in a less constrained continuum. In addition, we identify a feature
at 11.2 micron as the crystalline silicate forsterite, with only a minor
contribution from polycyclic aromatic hydrocarbons. The 5% crystalline silicate
fraction requires high temperatures such as those found in the immediate quasar
environment in order to counteract rapid destruction from cosmic rays.Comment: 2 figure
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