7,915 research outputs found
Non-perturbative Renormalization of Improved Staggered Bilinears
We compute Z-factors for general staggered bilinears on fine (a \approx 0.09
fm) MILC ensembles using both asqtad and HYP-smeared valence actions, comparing
the results to the predictions of one-loop perturbation theory. This is an
extension of previous work on the coarse (a \approx 0.12 fm) MILC ensembles. It
provides a laboratory for studying NPR methodology in the staggered context,
and is an important stepping stone for fully non-perturbative matching factors
in ongoing computations of B_K and other weak matrix elements. We also
implement non-exceptional RI/SMOM renormalization conditions using the asqtad
action and present first results.Comment: 7 pages, 4 figures. Contribution to the 30th International Symposium
on Lattice Field Theory, June 24-29, 2012, Cairns, Australi
Measurement-driven dynamics for a coherently-excited atom
The phenomenon of telegraphing in a measurement-driven two-level atom was noted in Cresser et al. [Cresser, J.D.; Barnett, S.M.; Jeffers, J.; Pegg, D.T. Opt. Commun. 2006, 264, 352361]. Here we introduce two quantitative measures of telegraphing: one based on the accumulated measurement record and one on the evolution of the quantum state. We use these to analyse the dynamics of the atom over a wide range of parameters. We find, in particular, that the measures provide broadly similar statistics when the measurements are frequent, but differ widely when measurements are sparse. This is in line with intuition, and demonstrates the utility of both measures
Toric codes and quantum doubles from two-body Hamiltonians
We present here a procedure to obtain the Hamiltonians of the toric code and Kitaev quantum double models as the low-energy limits of entirely two-body Hamiltonians. Our construction makes use of a new type of perturbation gadget based on error-detecting subsystem codes. The procedure is motivated by a projected entangled pair states (PEPS) description of the target models, and reproduces the target models' behavior using only couplings that are natural in terms of the original Hamiltonians. This allows our construction to capture the symmetries of the target models
Message Not Received? The Effects of Creditor Messaging and Pressure on Consumer Debt Management
Why do consumers avoid creditors when they send messages that put pressure on consumers to repay their debts? This behavior, called creditor avoidance, ultimately hurts consumers but many still engage in it despite it being against their best financial interests. To better understand factors that contribute to this behavior, this article uses unique data from a survey of 3,287 over-indebted consumers. Specifically, this research examines the association between creditor messaging and consumersâ creditor avoidance, and how consumersâ negative emotions about their debt circumstances are related to creditor avoidance behaviors. Findings indicate that debt-related shame and guilt, as well as the feeling of âdrowning in debt,â are associated with creditor avoidance behaviors. Other negative emotions, such as anxiety and unhappiness, however, are not. Further, creditor messages that match the consumersâ pre-message emotional state risk intensifying the adverse effect of creditor contact on consumers, thus increasing creditor avoidance. In these circumstances, creditor messages may act as an additional stressor rather than as a nudge towards repayment. These findings have implications for how credit organizations and policymakers communicate with, and assist, over-indebted consumers
In Mobile We Trust: How Mobile Reviews Can Overcome Consumer Distrust of User-Generated Reviews
In the context of user-generated content (UGC), mobile devices have made it easier for consumers to review products and services in a timely manner. In practice, some UGC sites differentiate between reviews posted from mobile versus non-mobile devices. For example, TripAdvisor uses a âvia mobileâ label to denote reviews from mobile devices. However, the extent to which such information impacts consumers is unknown. To address this gap, the authors use data from TripAdvisor and five experiments to examine how mobile impacts consumersâ perceptions of UGC reviews and their purchase intentions. They find that knowing that a review was posted from a mobile device leads consumers to perceive the review as more accurate, and, importantly, have higher purchase intentions. Interestingly, consumers assume that mobile reviews are more accurate due to the belief that writing reviews via mobile requires more effort and equate effort with the reviewer being more trustworthy. These effects are greater among skeptical consumers, implying that labeling of mobile reviews is a practice that can help overcome latent consumer distrust in UGC
Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background
We show that the soft X-ray excess in the Coma cluster can be explained by a
cosmic background of relativistic axions converting into photons in the cluster
magnetic field. We provide a detailed self-contained review of the cluster soft
X-ray excess, the proposed astrophysical explanations and the problems they
face, and explain how a 0.1-1 keV axion background naturally arises at
reheating in many string theory models of the early universe. We study the
morphology of the soft excess by numerically propagating axions through
stochastic, multi-scale magnetic field models that are consistent with
observations of Faraday rotation measures from Coma. By comparing to ROSAT
observations of the 0.2-0.4 keV soft excess, we find that the overall excess
luminosity is easily reproduced for
GeV. The resulting morphology is highly sensitive to the magnetic field
power spectrum. For Gaussian magnetic field models, the observed soft excess
morphology prefers magnetic field spectra with most power in coherence lengths
on scales over those with most power on scales. Within this scenario, we bound the mean energy of the
axion background to , the axion mass to , and derive a
lower bound on the axion-photon coupling GeV.Comment: 43 pages, 11 figure
Tailoring surface codes for highly biased noise
The surface code, with a simple modification, exhibits ultra-high error
correction thresholds when the noise is biased towards dephasing. Here, we
identify features of the surface code responsible for these ultra-high
thresholds. We provide strong evidence that the threshold error rate of the
surface code tracks the hashing bound exactly for all biases, and show how to
exploit these features to achieve significant improvement in logical failure
rate. First, we consider the infinite bias limit, meaning pure dephasing. We
prove that the error threshold of the modified surface code for pure dephasing
noise is , i.e., that all qubits are fully dephased, and this threshold
can be achieved by a polynomial time decoding algorithm. We demonstrate that
the sub-threshold behavior of the code depends critically on the precise shape
and boundary conditions of the code. That is, for rectangular surface codes
with standard rough/smooth open boundaries, it is controlled by the parameter
, where and are dimensions of the surface code lattice. We
demonstrate a significant improvement in logical failure rate with pure
dephasing for co-prime codes that have , and closely-related rotated
codes, which have a modified boundary. The effect is dramatic: the same logical
failure rate achievable with a square surface code and physical qubits can
be obtained with a co-prime or rotated surface code using only
physical qubits. Finally, we use approximate maximum likelihood decoding to
demonstrate that this improvement persists for a general Pauli noise biased
towards dephasing. In particular, comparing with a square surface code, we
observe a significant improvement in logical failure rate against biased noise
using a rotated surface code with approximately half the number of physical
qubits.Comment: 18+4 pages, 24 figures; v2 includes additional coauthor (ASD) and new
results on the performance of surface codes in the finite-bias regime,
obtained with beveled surface codes and an improved tensor network decoder;
v3 published versio
- âŠ