356,039 research outputs found
Origin of Magic Angular Momentum in a Quantum Dot under Strong Magnetic Field
This paper investigates origin of the extra stability associated with
particular values (magic numbers) of the total angular momentum of electrons in
a quantum dot under strong magnetic field. The ground-state energy,
distribution functions of density and angular momentum, and pair correlation
function are calculated in the strong field limit by numerical diagonalization
of the system containing up to seven electrons. It is shown that the composite
fermion picture explains the small magic numbers well, while a simple
geometrical picture does better as the magic number increases. Combination of
these two pictures leads to identification of all the magic numbers. Relation
of the magic-number states to the Wigner crystal and the fractional quantum
Hall state is discussed.Comment: 12 pages, 9 Postscript figures, uses jpsj.st
Number of Magic Squares From Parallel Tempering Monte Carlo
There are 880 magic squares of size 4 by 4, and 275,305,224 of size 5 by 5.
It seems very difficult if not impossible to count exactly the number of higher
order magic squares. We propose a method to estimate these numbers by Monte
Carlo simulating magic squares at finite temperature. One is led to perform low
temperature simulations of a system with many ground states that are separated
by energy barriers. The Parallel Tempering Monte Carlo method turns out to be
of great help here. Our estimate for the number of 6 by 6 magic squares is
0.17745(16) times 10**20.Comment: 8 pages, no figure
Resource Optimized Quantum Architectures for Surface Code Implementations of Magic-State Distillation
Quantum computers capable of solving classically intractable problems are
under construction, and intermediate-scale devices are approaching completion.
Current efforts to design large-scale devices require allocating immense
resources to error correction, with the majority dedicated to the production of
high-fidelity ancillary states known as magic-states. Leading techniques focus
on dedicating a large, contiguous region of the processor as a single
"magic-state distillation factory" responsible for meeting the magic-state
demands of applications. In this work we design and analyze a set of optimized
factory architectural layouts that divide a single factory into spatially
distributed factories located throughout the processor. We find that
distributed factory architectures minimize the space-time volume overhead
imposed by distillation. Additionally, we find that the number of distributed
components in each optimal configuration is sensitive to application
characteristics and underlying physical device error rates. More specifically,
we find that the rate at which T-gates are demanded by an application has a
significant impact on the optimal distillation architecture. We develop an
optimization procedure that discovers the optimal number of factory
distillation rounds and number of output magic states per factory, as well as
an overall system architecture that interacts with the factories. This yields
between a 10x and 20x resource reduction compared to commonly accepted single
factory designs. Performance is analyzed across representative application
classes such as quantum simulation and quantum chemistry.Comment: 16 pages, 14 figure
On Charged Mesoscopic Metallic Bubbles
We investigate the existence of stable charged metallic bubbles using the
shell correction method. We find that for a given mesoscopic system of n atoms
of a given metal and q less n (positive) elementary charges, a metallic bubble
turns out to have a lower total energy than a compact spherical cluster,
whenever the charge number q is larger than acritical charge number q_c. For a
magic number (n-q) of free electrons, the spherical metallic bubble may become
stable against fission.Comment: 14 pages in Latex and 5 figures in the eps forma
Results from MAGIC Observations of Extragalactic Relativistic Sources
The Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) experiment is an
array of two 17-meter telescopes located in the Canary Island of La Palma that
observes the very-high energy (VHE) gamma-ray sky in stereoscopic mode since
2009. MAGIC is distinguished by its low-energy threshold of approximately 50
GeV, which grants the system a unique potential in the study of distant
extragalactic sources whose gamma-ray emission is significantly attenuated due
to absorption by the extragalactic background light (EBL). The observation of
non-thermal gamma rays in the GeV-TeV range from extragalactic sources is a
characteristic signature of their relativistic nature and therefore
fundamentally important for our understanding of the physics of these objects.
Since the beginning of its stereo operation, MAGIC has observed a large number
of active galactic nuclei (AGN) of different classes, including several blazars
and distant quasars. In this paper we will review some of the most important
results of these observations.Comment: 7 pages, 2 figures, Observational Review talk given at HEPRO-III
Conference, Barcelona, June 201
The background from single electromagnetic subcascades for a stereo system of air Cherenkov telescopes
The MAGIC experiment, a very large Imaging Air Cherenkov Telescope (IACT)
with sensitivity to low energy (E < 100 GeV) VHE gamma rays, has been operated
since 2004. It has been found that the gamma/hadron separation in IACTs becomes
much more difficult below 100 GeV [Albert et al 2008] A system of two large
telescopes may eventually be triggered by hadronic events containing Cherenkov
light from only one electromagnetic subcascade or two gamma subcascades, which
are products of the single pi^0 decay. This is a possible reason for the
deterioration of the experiment's sensitivity below 100 GeV. In this paper a
system of two MAGIC telescopes working in stereoscopic mode is studied using
Monte Carlo simulations. The detected images have similar shapes to that of
primary gamma-rays and they have small sizes (mainly below 400 photoelectrons
(p.e.)) which correspond to an energy of primary gamma-rays below 100 GeV. The
background from single or two electromagnetic subcascdes is concentrated at
energies below 200 GeV. Finally the number of background events is compared to
the number of VHE gamma-ray excess events from the Crab Nebula. The
investigated background survives simple cuts for sizes below 250 p.e. and thus
the experiment's sensitivity deteriorates at lower energies.Comment: 15 pages, 7 figures, published in Journ.of Phys.
A Puzzler\u27s Paradise
Listed below are 34 kinds of word puzzles, games and curiosities, each one in scrambled form. Your assignment is to rearrange the letters of each one into its correct order. Simple enough? Of course! Why 34 scrambles, instead of some number that shows a healthy respect for the decimal system? Because 34 happens to be the total of each row, column and main diagonal in a magic square of the fourth order - sufficient reason
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