1,270 research outputs found
Entangled Quantum States Generated by Shor's Factoring Algorithm
The intermediate quantum states of multiple qubits, generated during the
operation of Shor's factoring algorithm are analyzed. Their entanglement is
evaluated using the Groverian measure. It is found that the entanglement is
generated during the pre-processing stage of the algorithm and remains nearly
constant during the quantum Fourier transform stage. The entanglement is found
to be correlated with the speedup achieved by the quantum algorithm compared to
classical algorithms.Comment: 7 pages, 4 figures submitted to Phys. Rev.
Magnetothermal Transport in Spin-Ladder Systems
We study a theoretical model for the magnetothermal conductivity of a
spin-1/2 ladder with low exchange coupling () subject to a strong
magnetic field . Our theory for the thermal transport accounts for the
contribution of spinons coupled to lattice phonon modes in the one-dimensional
lattice. We employ a mapping of the ladder Hamiltonian onto an XXZ spin-chain
in a weaker effective field B_{eff}=B-B_{0}B_{0}=(B_{c1}+B_{c2})/2B{\rm
Br_4(C_5H_{12}N)_2}$ (BPCB).Comment: 14 pages, 4 figure
Holographic description of Narain CFTs and their code-based ensembles
We provide a precise relation between an ensemble of Narain conformal field
theories (CFTs) with central charge , and a sum of
Chern-Simons theories on different handlebody topologies. We begin by reviewing
the general relation of additive codes to Narain CFTs. Then we describe a
holographic duality between any given Narain theory and a pure Chern-Simons
theory on a handlebody manifold. We proceed to consider an ensemble of Narain
theories, defined in terms of an ensemble of codes of length over for prime . We show that averaging over this
ensemble is holographically dual to a level-
Chern-Simons theory, summed over a finite number of inequivalent classes of
handlebody topologies. In the limit of large the ensemble approaches the
ensemble of all Narain theories, and its bulk dual becomes equivalent to
"U(1)-gravity" - the sum of the pertubative part of the Chern-Simons
wavefunction over all possible handlebodies - providing a bulk microscopic
definition for this theory. Finally, we reformulate the sum over handlebodies
in terms of Hecke operators, paving the way for generalizations.Comment: 53 page
Formation of Multipartite Entanglement Using Random Quantum Gates
The formation of multipartite quantum entanglement by repeated operation of
one and two qubit gates is examined. The resulting entanglement is evaluated
using two measures: the average bipartite entanglement and the Groverian
measure. A comparison is made between two geometries of the quantum register: a
one dimensional chain in which two-qubit gates apply only locally between
nearest neighbors and a non-local geometry in which such gates may apply
between any pair of qubits. More specifically, we use a combination of random
single qubit rotations and a fixed two-qubit gate such as the controlled-phase
gate. It is found that in the non-local geometry the entanglement is generated
at a higher rate. In both geometries, the Groverian measure converges to its
asymptotic value more slowly than the average bipartite entanglement. These
results are expected to have implications on different proposed geometries of
future quantum computers with local and non-local interactions between the
qubits.Comment: 7 pages, 5 figure
The Stellar CME-flare relation: What do historic observations reveal?
Solar CMEs and flares have a statistically well defined relation, with more
energetic X-ray flares corresponding to faster and more massive CMEs. How this
relation extends to more magnetically active stars is a subject of open
research. Here, we study the most probable stellar CME candidates associated
with flares captured in the literature to date, all of which were observed on
magnetically active stars. We use a simple CME model to derive masses and
kinetic energies from observed quantities, and transform associated flare data
to the GOES 1--8~\AA\ band. Derived CME masses range from to
~g. Associated flare X-ray energies range from to
~erg. Stellar CME masses as a function of associated flare energy
generally lie along or below the extrapolated mean for solar events. In
contrast, CME kinetic energies lie below the analogous solar extrapolation by
roughly two orders of magnitude, indicating approximate parity between flare
X-ray and CME kinetic energies. These results suggest that the CMEs associated
with very energetic flares on active stars are more limited in terms of the
ejecta velocity than the ejecta mass, possibly because of the restraining
influence of strong overlying magnetic fields and stellar wind drag. Lower CME
kinetic energies and velocities present a more optimistic scenario for the
effects of CME impacts on exoplanets in close proximity to active stellar
hosts.Comment: 23 pages, 3 tables, 4 figures, accepted by Ap
Halo detection via large-scale Bayesian inference
We present a proof-of-concept of a novel and fully Bayesian methodology
designed to detect halos of different masses in cosmological observations
subject to noise and systematic uncertainties. Our methodology combines the
previously published Bayesian large-scale structure inference algorithm, HADES,
and a Bayesian chain rule (the Blackwell-Rao Estimator), which we use to
connect the inferred density field to the properties of dark matter halos. To
demonstrate the capability of our approach we construct a realistic galaxy mock
catalogue emulating the wide-area 6-degree Field Galaxy Survey, which has a
median redshift of approximately 0.05. Application of HADES to the catalogue
provides us with accurately inferred three-dimensional density fields and
corresponding quantification of uncertainties inherent to any cosmological
observation. We then use a cosmological simulation to relate the amplitude of
the density field to the probability of detecting a halo with mass above a
specified threshold. With this information we can sum over the HADES density
field realisations to construct maps of detection probabilities and demonstrate
the validity of this approach within our mock scenario. We find that the
probability of successful of detection of halos in the mock catalogue increases
as a function of the signal-to-noise of the local galaxy observations. Our
proposed methodology can easily be extended to account for more complex
scientific questions and is a promising novel tool to analyse the cosmic
large-scale structure in observations.Comment: 17 pages, 13 figures. Accepted for publication in MNRAS following
moderate correction
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