5,055 research outputs found
Parallelism for Quantum Computation with Qudits
Robust quantum computation with d-level quantum systems (qudits) poses two
requirements: fast, parallel quantum gates and high fidelity two-qudit gates.
We first describe how to implement parallel single qudit operations. It is by
now well known that any single-qudit unitary can be decomposed into a sequence
of Givens rotations on two-dimensional subspaces of the qudit state space.
Using a coupling graph to represent physically allowed couplings between pairs
of qudit states, we then show that the logical depth of the parallel gate
sequence is equal to the height of an associated tree. The implementation of a
given unitary can then optimize the tradeoff between gate time and resources
used. These ideas are illustrated for qudits encoded in the ground hyperfine
states of the atomic alkalies Rb and Cs. Second, we provide a
protocol for implementing parallelized non-local two-qudit gates using the
assistance of entangled qubit pairs. Because the entangled qubits can be
prepared non-deterministically, this offers the possibility of high fidelity
two-qudit gates.Comment: 9 pages, 3 figure
Group finding in the stellar halo using M-giants in 2MASS: An extended view of the Pisces Overdensity?
A density based hierarchical group-finding algorithm is used to identify
stellar halo structures in a catalog of M-giants from the Two Micron All Sky
Survey (2MASS). The intrinsic brightness of M-giant stars means that this
catalog probes deep into the halo where substructures are expected to be
abundant and easy to detect. Our analysis reveals 16 structures at high
Galactic latitude (greater than 15 degree), of which 10 have been previously
identified. Among the six new structures two could plausibly be due to masks
applied to the data, one is associated with a strong extinction region and one
is probably a part of the Monoceros ring. Another one originates at low
latitudes, suggesting some contamination from disk stars, but also shows
protrusions extending to high latitudes, implying that it could be a real
feature in the stellar halo. The last remaining structure is free from the
defects discussed above and hence is very likely a satellite remnant. Although
the extinction in the direction of the structure is very low, the structure
does match a low temperature feature in the dust maps. While this casts some
doubt on its origin, the low temperature feature could plausibly be due to real
dust in the structure itself. The angular position and distance of this
structure encompass the Pisces overdensity traced by RR Lyraes in Stripe 82 of
the Sloan Digital Sky Survey (SDSS). However, the 2MASS M-giants indicate that
the structure is much more extended than what is visible with the SDSS, with
the point of peak density lying just outside Stripe 82. The morphology of the
structure is more like a cloud than a stream and reminiscent of that seen in
simulations of satellites disrupting along highly eccentric orbits.Comment: Accepted for publication in Ap
3D stellar kinematics at the Galactic center: measuring the nuclear star cluster spatial density profile, black hole mass, and distance
We present 3D kinematic observations of stars within the central 0.5 pc of
the Milky Way nuclear star cluster using adaptive optics imaging and
spectroscopy from the Keck telescopes. Recent observations have shown that the
cluster has a shallower surface density profile than expected for a dynamically
relaxed cusp, leading to important implications for its formation and
evolution. However, the true three dimensional profile of the cluster is
unknown due to the difficulty in de-projecting the stellar number counts. Here,
we use spherical Jeans modeling of individual proper motions and radial
velocities to constrain for the first time, the de-projected spatial density
profile, cluster velocity anisotropy, black hole mass (), and
distance to the Galactic center () simultaneously. We find that the inner
stellar density profile of the late-type stars, to
have a power law slope , much more shallow than
the frequently assumed Bahcall Wolf slope of . The measured
slope will significantly affect dynamical predictions involving the cluster,
such as the dynamical friction time scale. The cluster core must be larger than
0.5 pc, which disfavors some scenarios for its origin. Our measurement of
and
kpc is consistent with that derived from stellar
orbits within 1 of Sgr A*. When combined with the orbit of
S0-2, the uncertainty on is reduced by 30% ( kpc).
We suggest that the MW NSC can be used in the future in combination with
stellar orbits to significantly improve constraints on .Comment: 7 pages, 3 figures, 2 tables, ApJL accepte
Angular Alignment Testing of Laser Mirror Mounts Under Temperature Cycling
A number of commercial and custom-built laser mirror mounts were tested for angular alignment sensitivity during temperature cycling from room temperature (20 C) to 40 C. A Nd:YAG laser beam was reflected off a mirror that was held by the mount under test and was directed to a position-sensitive detector. Horizontal and vertical movement of the reflected beam was recorded, and the angular movement, as a function of temperature (coefficient of thermal tilt (CTT)) was calculated from these data. In addition, the amount of hysteresis in the movement after cycling from room temperature to 40 C and back was determined. All commercial mounts showed greater angular movement than the simpler National Aeronautics and Space Administration Lidar Atmospheric Sensing Experiment (NASA LASE) custom mirror mounts
Tracing Galaxy Formation with Stellar Halos I: Methods
If the favored hierarchical cosmological model is correct, then the Milky Way
system should have accreted ~100-200 luminous satellite galaxies in the past
\~12 Gyr. We model this process using a hybrid semi-analytic plus N-body
approach which distinguishes explicitly between the evolution of light and dark
matter in accreted satellites. This distinction is essential to our ability to
produce a realistic stellar halo, with mass and density profile much like that
of our own Galaxy, and a surviving satellite population that matches the
observed number counts and structural parameter distributions of the satellite
galaxies of the Milky Way. Our model stellar halos have density profiles which
typically drop off with radius faster than those of the dark matter. They are
assembled from the inside out, with the majority of mass (~80%) coming from the
\~15 most massive accretion events. The satellites that contribute to the
stellar halo have median accretion times of ~9 Gyr in the past, while surviving
satellite systems have median accretion times of ~5 Gyr in the past. This
implies that stars associated with the inner halo should be quite different
chemically from stars in surviving satellites and also from stars in the outer
halo or those liberated in recent disruption events. We briefly discuss the
expected spatial structure and phase space structure for halos formed in this
manner. Searches for this type of structure offer a direct test of whether
cosmology is indeed hierarchical on small scales.Comment: 22 pages, 16 figures, submitted to Ap
Quantum circuits with uniformly controlled one-qubit gates
Uniformly controlled one-qubit gates are quantum gates which can be
represented as direct sums of two-dimensional unitary operators acting on a
single qubit. We present a quantum gate array which implements any n-qubit gate
of this type using at most 2^{n-1} - 1 controlled-NOT gates, 2^{n-1} one-qubit
gates and a single diagonal n-qubit gate. The circuit is based on the so-called
quantum multiplexor, for which we provide a modified construction. We
illustrate the versatility of these gates by applying them to the decomposition
of a general n-qubit gate and a local state preparation procedure. Moreover, we
study their implementation using only nearest-neighbor gates. We give upper
bounds for the one-qubit and controlled-NOT gate counts for all the
aforementioned applications. In all four cases, the proposed circuit topologies
either improve on or achieve the previously reported upper bounds for the gate
counts. Thus, they provide the most efficient method for general gate
decompositions currently known.Comment: 8 pages, 10 figures. v2 has simpler notation and sharpens some
result
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Using scenarios to explore UK upland futures
Uplands around the world are facing significant social, economic and environmental changes, and decision-makers need to better understand what the future may hold if they are to adapt and maintain upland goods and services. This paper draws together all major research comprising eight studies that have used scenarios to describe possible futures for UK uplands. The paper evaluates which scenarios are perceived by stakeholders to be most likely and desirable, and assesses the benefits and drawbacks of the scenario methods used in UK uplands to date. Stakeholders agreed that the most desirable and likely scenario would be a continuation of hill farming (albeit at reduced levels) based on cross-compliance with environmental measures. The least desirable scenario is a withdrawal of government financial support for hill farming. Although this was deemed by stakeholders to be the least likely scenario, the loss of government support warrants close attention due to its potential implications for the local economy. Stakeholders noted that the environmental implications of this scenario are much less clear-cut. As such, there is an urgent need to understand the full implications of this scenario, so that upland stakeholders can adequately prepare, and policy-makers can better evaluate the likely implications of different policy options. The paper concludes that in future, upland scenario research needs to: (1) better integrate in-depth and representative participation from stakeholders during both scenario development and evaluation; and (2) make more effective use of visualisation techniques and simulation models
Hybrid Reactions to Phytotoxic Effects of The Corn Herbicide, Eradicane Extra
Although corn hybrids are primarily evaluated only for yield performance in the Kentucky Hybrid Corn Performance Test, the 1984 test (Poneleit and Evans, 1985) provided a unique opportunity to evaluate hybrid reactions to an unusual hybrid-herbicide interacting Of seven non-virus test locations, four were treated with Eradicane Extra or Eradicane for weed control. At the Princeton location Eradicane Extra, at 8 pints/acre, was used for johnsongrass rhizome suppression and seedling control. In late July, a routine check revealed that numerous plants had unusual appearances that were similar to abnormalities reported earlier as caused by Eptam and Eradicane (Poneleit et aI, 1975). Subsequent observations confirmed the severity of damage at the Princeton test site and reports of similar hybrid reactions from farmer fields prompted the collection of apparent herbicide damage data from the replicated Princeton test. The other performance test sites where Eradicane Extra or Eradicane was applied did not show significant plant abnormalities. Apparently the appearance of phytotoxic effects owing to Eradicane Extra are sporadic and strongly influenced by specific interaction of environmental factors. It was postulated that this injury occurrence in 1984 was the result of excessive rainfall four to six weeks after planting. Dichlormid (safener) is very water soluble and could have been leached away from the corn roots, and thus not available to protect the corn from EPTC
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