4,391 research outputs found
Prescription for experimental determination of the dynamics of a quantum black box
We give an explicit prescription for experimentally determining the evolution
operators which completely describe the dynamics of a quantum mechanical black
box -- an arbitrary open quantum system. We show necessary and sufficient
conditions for this to be possible, and illustrate the general theory by
considering specifically one and two quantum bit systems. These procedures may
be useful in the comparative evaluation of experimental quantum measurement,
communication, and computation systems.Comment: 6 pages, Revtex. Submitted to J. Mod. Op
Tensor product representation of topological ordered phase: necessary symmetry conditions
The tensor product representation of quantum states leads to a promising
variational approach to study quantum phase and quantum phase transitions,
especially topological ordered phases which are impossible to handle with
conventional methods due to their long range entanglement. However, an
important issue arises when we use tensor product states (TPS) as variational
states to find the ground state of a Hamiltonian: can arbitrary variations in
the tensors that represent ground state of a Hamiltonian be induced by local
perturbations to the Hamiltonian? Starting from a tensor product state which is
the exact ground state of a Hamiltonian with topological order,
we show that, surprisingly, not all variations of the tensors correspond to the
variation of the ground state caused by local perturbations of the Hamiltonian.
Even in the absence of any symmetry requirement of the perturbed Hamiltonian,
one necessary condition for the variations of the tensors to be physical is
that they respect certain symmetry. We support this claim by
calculating explicitly the change in topological entanglement entropy with
different variations in the tensors. This finding will provide important
guidance to numerical variational study of topological phase and phase
transitions. It is also a crucial step in using TPS to study universal
properties of a quantum phase and its topological order.Comment: 10 pages, 6 figure
Nuclear Magnetic Resonance Quantum Computing Using Liquid Crystal Solvents
Liquid crystals offer several advantages as solvents for molecules used for
nuclear magnetic resonance quantum computing (NMRQC). The dipolar coupling
between nuclear spins manifest in the NMR spectra of molecules oriented by a
liquid crystal permits a significant increase in clock frequency, while short
spin-lattice relaxation times permit fast recycling of algorithms, and save
time in calibration and signal-enhancement experiments. Furthermore, the use of
liquid crystal solvents offers scalability in the form of an expanded library
of spin-bearing molecules suitable for NMRQC. These ideas are demonstrated with
the successful execution of a 2-qubit Grover search using a molecule
(CHCl) oriented in a liquid crystal and a clock speed eight
times greater than in an isotropic solvent. Perhaps more importantly, five
times as many logic operations can be executed within the coherence time using
the liquid crystal solvent.Comment: Minor changes. Published in Appl. Phys. Lett. v.75, no.22, 29 Nov
1999, p.3563-356
Induced Nested Galactic Bars Inside Assembling Dark Matter Halos
We investigate the formation and evolution of nested bar systems in disk
galaxies in a cosmological setting by following the development of an isolated
dark matter (DM) and baryon density perturbation. The disks form within the
assembling triaxial DM halos and the feedback from the stellar evolution is
accounted for in terms of supernovae and OB stellar winds. Focusing on a
representative model, we show the formation of an oval disk and of a first
generation of nested bars with characteristic sub-kpc and a few kpc sizes. The
system evolves through successive dynamical couplings and decouplings, forcing
the gas inwards and settles in a state of resonant coupling. The inflow rate
can support a broad range of activity within the central kpc, from quasar- to
Seyfert-types, supplemented by a vigorous star formation as a by-product. The
initial bar formation is triggered in response to the tidal torques from the
triaxial DM halo, which acts as a finite perturbation. This first generation of
bars does not survive for more than 4--5 Gyr: by that time the secondary bar
has totally dissolved, while the primary one has very substantially weakened,
reduced to a fat oval. This evolution is largely due to chaos introduced by the
interaction of the multiple non-axisymmetric components.Comment: 4 pages, 4 figures, 1 mpeg animation. To be published by the
Astrophysical Journal Letters. The animation can be found at
http://www.pa.uky.edu/~shlosman/research/galdyn/movies.html Replaced with an
updated version (small text corrections
OCS Leasing and Auctions: Incentives and the Performance of Alternative Bidding Institutions
In Watt v. Energy Action Educational Foundation, the Supreme Court rebutted a challenge to the federal government\u27s mix of \u27nontraditional\u27 outer continental shelf lease-auction mechanisms authorized under the 1978 OCS Amendments. The issues of this case addressed here include: the economic intent of the congressional language; incentive properties of various of the authorized auction processes; methodological shortcomings inherent in the implicit congressional directive for field experimentation; and, the usefulness of laboratory experimental economics in answering relevant auction-policy questions. The discussion of experimental economics includes evidence already gained from laboratory experiments relating to hypotheses about auction-market performance
Programmable quantum gate arrays
We show how to construct quantum gate arrays that can be programmed to
perform different unitary operations on a data register, depending on the input
to some program register. It is shown that a universal quantum gate array - a
gate array which can be programmed to perform any unitary operation - exists
only if one allows the gate array to operate in a probabilistic fashion. The
universal quantum gate array we construct requires an exponentially smaller
number of gates than a classical universal gate array.Comment: 3 pages, REVTEX. Submitted to Phys. Rev. Let
Performance of two handheld NIR spectrometers to quantify crude protein of composite animal forage and feedstuff
Two handheld near infrared (NIR) spectrometers were used to quantify crude protein (CP) content of mixed forage and feedstuff composed of Sweet Bran, distiller’s grains, corn silage, and corn stalk. First was a transportable spectrometer, which measured in the visible and NIR ranges (320–2500 nm) with a spectral interval of 1 nm (H1). Second was a smartphone spectrometer, which measured from 900–1700 nm with a spectral interval of 4 nm (H2). Spectral data of 147 forage and feed samples were collected by both handheld instruments and split into calibration (n= 120) and validation (n= 27) sets. For H1, only absorbances in the NIR region (780–2500 nm) were used in the multivariate analyses, while for H2, absorbances in the second and third overtone regions (940–1660 nm) were used. Principal component analysis (PCA) and partial least squares (PLS) regression models were developed using mean-centered data that had been preprocessed using standard normal variate (SNV) or Savitzky-Golay first derivative (SG1) or second derivative (SG2) algorithm. PCA models showed two major groups—one with Sweet Bran and distillers grains, and the other with corn silage and corn stalk. Using H1 spectra, the PLS regression model that best predicted CP followed SG1 preprocessing. This model had low root mean square error of prediction (RMSEP= 2.22%) and high ratio of prediction to deviation (RPD= 5.24). With H2 spectra, the model best predicting CP was based on SG2 preprocessing, returning RMSEP= 2.05% and RPD= 5.74. These values were not practically different than those of H1, indicating similar performance of the two devices despite having absorbance measurements only in the second and third overtone regions with H2. The result of this study showed that both handheld NIR instruments can accurately measure forage and feed CP during screening, quality, and process control applications
Asphericity, Interaction, and Dust in the Type II-P/II-L Supernova 2013ej in Messier 74
SN 2013ej is a well-studied core-collapse supernova (SN) that stemmed from a
directly identified red supergiant (RSG) progenitor in galaxy M74. The source
exhibits signs of substantial geometric asphericity, X-rays from persistent
interaction with circumstellar material (CSM), thermal emission from warm dust,
and a light curve that appears intermediate between supernovae of Types II-P
and II-L. The proximity of this source motivates a close inspection of these
physical characteristics and their potential interconnection. We present
multi-epoch spectropolarimetry of SN 2013ej during the first 107 days, and deep
optical spectroscopy and ultraviolet through infrared photometry past ~800
days. SN 2013ej exhibits the strongest and most persistent continuum and line
polarization ever observed for a SN of its class during the recombination
phase. Modeling indicates that the data are consistent with an oblate
ellipsoidal photosphere, viewed nearly edge-on, and probably augmented by
optical scattering from circumstellar dust. We suggest that interaction with an
equatorial distribution of CSM, perhaps the result of binary evolution, is
responsible for generating the photospheric asphericity. Relatedly, our
late-time optical imaging and spectroscopy shows that asymmetric CSM
interaction is ongoing, and the morphology of broad H-alpha emission from
shock-excited ejecta provides additional evidence that the geometry of the
interaction region is ellipsoidal. Alternatively, a prolate ellipsoidal
geometry from an intrinsically bipolar explosion is also a plausible
interpretation of the data, but would probably require a ballistic jet of
radioactive material capable of penetrating the hydrogen envelope early in the
recombination phase (abridged).Comment: Post-proof edit. Accepted to ApJ on Nov. 23 2016; 21 pages, 16
figure
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