4,864 research outputs found
Experimental quantum verification in the presence of temporally correlated noise
Growth in the complexity and capabilities of quantum information hardware
mandates access to practical techniques for performance verification that
function under realistic laboratory conditions. Here we experimentally
characterise the impact of common temporally correlated noise processes on both
randomised benchmarking (RB) and gate-set tomography (GST). We study these
using an analytic toolkit based on a formalism mapping noise to errors for
arbitrary sequences of unitary operations. This analysis highlights the role of
sequence structure in enhancing or suppressing the sensitivity of quantum
verification protocols to either slowly or rapidly varying noise, which we
treat in the limiting cases of quasi-DC miscalibration and white noise power
spectra. We perform experiments with a single trapped Yb ion as a
qubit and inject engineered noise () to probe protocol
performance. Experiments on RB validate predictions that the distribution of
measured fidelities over sequences is described by a gamma distribution varying
between approximately Gaussian for rapidly varying noise, and a broad, highly
skewed distribution for the slowly varying case. Similarly we find a strong
gate set dependence of GST in the presence of correlated errors, leading to
significant deviations between estimated and calculated diamond distances in
the presence of correlated errors. Numerical simulations demonstrate
that expansion of the gate set to include negative rotations can suppress these
discrepancies and increase reported diamond distances by orders of magnitude
for the same error processes. Similar effects do not occur for correlated
or errors or rapidly varying noise processes,
highlighting the critical interplay of selected gate set and the gauge
optimisation process on the meaning of the reported diamond norm in correlated
noise environments.Comment: Expanded and updated analysis of GST, including detailed examination
of the role of gauge optimization in GST. Full GST data sets and
supplementary information available on request from the authors. Related
results available from
http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm
Manifolds associated with -colored regular graphs
In this article we describe a canonical way to expand a certain kind of
-colored regular graphs into closed -manifolds by
adding cells determined by the edge-colorings inductively. We show that every
closed combinatorial -manifold can be obtained in this way. When ,
we give simple equivalent conditions for a colored graph to admit an expansion.
In addition, we show that if a -colored regular graph
admits an -skeletal expansion, then it is realizable as the moment graph of
an -dimensional closed -manifold.Comment: 20 pages with 9 figures, in AMS-LaTex, v4 added a new section on
reconstructing a space with a -action for which its moment graph is
a given colored grap
Time and energy constraints and the relationships between currencies in foraging theory
Measured foraging strategies often cluster around values that maximize the ratio of energy gained over energy spent while foraging (efficiency), rather than values that would maximize the long-term net rate of energy gain (rate). The reasons for this are not understood. This paper focuses on time and energy constraints while foraging to illustrate the relationship between efficiency and rate-maximizing strategies and develops models that provide a simple framework to analyze foraging strategies in two distinct foraging contexts. We assume that while capturing and ingesting food for their own use (which we term feeding), foragers behave so as to maximize the total net daily energetic gain. When gathering food for others or for storage (which we term provisioning), we assume that foragers behave so as to maximize the total daily delivery, subject to meeting their own energetic requirements. In feeding contexts, the behavior maximizing total net daily gain also maximizes efficiency when daily intake is limited by the assimilation capacity. In contrast, when time available to forage sets the limit to gross intake, the behavior maximizing total net daily gain also maximizes rate. In provisioning contexts, when daily delivery is constrained by the energy needed to power self-feeding, maximizing efficiency ensures the highest total daily delivery. When time needed to recoup energetic expenditure limits total delivery, a low self-feeding rate relative to the rate of energy expenditure favors efficient strategies. However, as the rate of self-feeding increases, foraging behavior deviates from efficiency maximization in the direction predicted by rate maximization. Experimental manipulations of the rate of self-feeding in provisioning contexts could be a powerful tool to explore the relationship between rate and efficiency-maximizing behavio
Quantum simulation of the Klein paradox with trapped ions
We report on quantum simulations of relativistic scattering dynamics using
trapped ions. The simulated state of a scattering particle is encoded in both
the electronic and vibrational state of an ion, representing the discrete and
continuous components of relativistic wave functions. Multiple laser fields and
an auxiliary ion simulate the dynamics generated by the Dirac equation in the
presence of a scattering potential. Measurement and reconstruction of the
particle wave packet enables a frame-by-frame visualization of the scattering
processes. By precisely engineering a range of external potentials we are able
to simulate text book relativistic scattering experiments and study Klein
tunneling in an analogue quantum simulator. We describe extensions to solve
problems that are beyond current classical computing capabilities.Comment: 3 figures, accepted for publication in PR
Construction and characterization of a BAC-library for a key pollinator, the bumblebee Bombus terrestris L
Abstract.: The primitively social bumblebee Bombus terrestris is an ecological model species as well as an important agricultural pollinator. As part of the ongoing development of genomic resources for this model organism, we have constructed a publicly available bacterial artificial chromosome (BAC) library from males of a field-derived colony. We have shown that this library has a high coverage, which allows any particular sequence to be retrieved from at least one clone with a probability of 99.7%. We have further demonstrated the library's usefulness by successfully screening it with probes derived both from previously described B. terrestris genes and candidate genes from another bumblebee species and the honeybee. This library will facilitate genomic studies in B. terrestris and will allow for novel comparative studies in the social Hymenopter
Is there Quark Matter in (Low-Mass) Pulsars?
The effect of the QCD phase transition is studied for the mass-radius
relation of compact stars and for hot and dense matter at a given proton
fraction used as input in core-collapse supernova simulations. The phase
transitions to the 2SC and CFL color superconducting phases lead to stable
hybrid star configurations with a pure quark matter core. In supernova
explosions quark matter could be easily produced due to -equilibrium,
small proton fractions and nonvanishing temperatures. A low critical density
for the phase transition to quark matter is compatible with present pulsar mass
measurements.Comment: 4 pages, 3 figures, talk given at the QM2008 conference, Jaipur,
India, February 4-10, 2008, JPG in pres
Pushing 1D CCSNe to explosions: model and SN 1987A
We report on a method, PUSH, for triggering core-collapse supernova
explosions of massive stars in spherical symmetry. We explore basic explosion
properties and calibrate PUSH such that the observables of SN1987A are
reproduced. Our simulations are based on the general relativistic hydrodynamics
code AGILE combined with the detailed neutrino transport scheme IDSA for
electron neutrinos and ALS for the muon and tau neutrinos. To trigger
explosions in the otherwise non-exploding simulations, we rely on the
neutrino-driven mechanism. The PUSH method locally increases the energy
deposition in the gain region through energy deposition by the heavy neutrino
flavors. Our setup allows us to model the explosion for several seconds after
core bounce. We explore the progenitor range 18-21M. Our studies
reveal a distinction between high compactness (HC) and low compactness (LC)
progenitor models, where LC models tend to explore earlier, with a lower
explosion energy, and with a lower remnant mass. HC models are needed to obtain
explosion energies around 1 Bethe, as observed for SN1987A. However, all the
models with sufficiently high explosion energy overproduce Ni. We
conclude that fallback is needed to reproduce the observed nucleosynthesis
yields. The nucleosynthesis yields of Ni depend sensitively on the
electron fraction and on the location of the mass cut with respect to the
initial shell structure of the progenitor star. We identify a progenitor and a
suitable set of PUSH parameters that fit the explosion properties of SN1987A
when assuming 0.1M of fallback. We predict a neutron star with a
gravitational mass of 1.50M. We find correlations between explosion
properties and the compactness of the progenitor model in the explored
progenitors. However, a more complete analysis will require the exploration of
a larger set of progenitors with PUSH.Comment: revised version as accepted by ApJ (results unchanged, text modified
for clarification, a few references added); 26 pages, 20 figure
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