14,248 research outputs found
Quantum Phase Transition in the Sub-Ohmic Spin-Boson Model: Extended Coherent-state Approach
We propose a general extended coherent state approach to the qubit (or
fermion) and multi-mode boson coupling systems. The application to the
spin-boson model with the discretization of a bosonic bath with arbitrary
continuous spectral density is described in detail, and very accurate solutions
can be obtained. The quantum phase transition in the nontrivial sub-Ohmic case
can be located by the fidelity and the order-parameter critical exponents for
the bath exponents can be correctly given by the fidelity
susceptibility, demonstrating the strength of the approach.Comment: 4 pages, 3 figure
Quantum phase transitions in coupled two-level atoms in a single-mode cavity
The dipole-coupled two-level atoms(qubits) in a single-mode resonant cavity
is studied by extended bosonic coherent states. The numerically exact solution
is presented. For finite systems, the first-order quantum phase transitions
occur at the strong interatomic interaction. Similar to the original Dicke
model, this system exhibits a second-order quantum phase transition from the
normal to the superradiant phases. Finite-size scaling for several observables,
such as the average fidelity susceptibility, the order parameter, and
concurrence are performed for different interatomic interactions. The obtained
scaling exponents suggest that interatomic interactions do not change the
universality class.Comment: 13 pages, 5 figure
Accurate numerical solution to the finite-size Dicke model
By using extended bosonic coherent states, a new technique to solve the Dicke
model exactly is proposed in the numerical sense. The accessible system size is
two orders of magnitude higher than that reported in literature. Finite-size
scaling for several observables, such as the ground-state energy, Berry phase,
and concurrence are analyzed. The existing discrepancy for the scaling exponent
of the concurrence is reconciled.Comment: 4 pages, 5 figures. Phys. Rev. A (in press, a Rapid Communication
WheaCha: A Method for Explaining the Predictions of Models of Code
Attribution methods have emerged as a popular approach to interpreting model
predictions based on the relevance of input features. Although the feature
importance ranking can provide insights of how models arrive at a prediction
from a raw input, they do not give a clear-cut definition of the key features
models use for the prediction. In this paper, we present a new method, called
WheaCha, for explaining the predictions of code models. Although WheaCha
employs the same mechanism of tracing model predictions back to the input
features, it differs from all existing attribution methods in crucial ways.
Specifically, WheaCha divides an input program into "wheat" (i.e., the defining
features that are the reason for which models predict the label that they
predict) and the rest "chaff" for any prediction of a learned code model. We
realize WheaCha in a tool, HuoYan, and use it to explain four prominent code
models: code2vec, seq-GNN, GGNN, and CodeBERT. Results show (1) HuoYan is
efficient - taking on average under twenty seconds to compute the wheat for an
input program in an end-to-end fashion (i.e., including model prediction time);
(2) the wheat that all models use to predict input programs is made of simple
syntactic or even lexical properties (i.e., identifier names); (3) Based on
wheat, we present a novel approach to explaining the predictions of code models
through the lens of training data
Duodenum Exclusion Alone Is Sufficient to Reduce Fasting Blood Glucose in Non-Obese Diabetic Goto-Kakizaki Rats
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