15,892 research outputs found
Bell's Inequality and Entanglement in Qubits
We propose an alternative evaluation of quantum entanglement by measuring the
maximum violation of the Bell's inequality without performing a partial trace
operation. This proposal is demonstrated by bridging the maximum violation of
the Bell's inequality and the concurrence of a pure state in an -qubit
system, in which one subsystem only contains one qubit and the state is a
linear combination of two product states. We apply this relation to the ground
states of four qubits in the Wen-Plaquette model and show that they are
maximally entangled. A topological entanglement entropy of the Wen-Plaquette
model could be obtained by relating the upper bound of the maximum violation of
the Bell's inequality to the concurrences of a pure state with respect to
different bipartitions.Comment: 10 page
Evolution of entanglement spectra under generic quantum dynamics
We characterize the early stages of the approach to equilibrium in isolated
quantum systems through the evolution of the entanglement spectrum. We find
that the entanglement spectrum of a subsystem evolves with at least three
distinct timescales. First, on an o(1) timescale, independent of system or
subsystem size and the details of the dynamics, the entanglement spectrum
develops nearest-neighbor level repulsion. The second timescale sets in when
the light-cone has traversed the subsystem. Between these two times, the
density of states of the reduced density matrix takes a universal, scale-free
1/f form; thus, random-matrix theory captures the local statistics of the
entanglement spectrum but not its global structure. The third time scale is
that on which the entanglement saturates; this occurs well after the light-cone
traverses the subsystem. Between the second and third times, the entanglement
spectrum compresses to its thermal Marchenko-Pastur form. These features hold
for chaotic Hamiltonian and Floquet dynamics as well as a range of quantum
circuit models.Comment: 12 pages, 15 figure
Distributionally Robust Semi-Supervised Learning for People-Centric Sensing
Semi-supervised learning is crucial for alleviating labelling burdens in
people-centric sensing. However, human-generated data inherently suffer from
distribution shift in semi-supervised learning due to the diverse biological
conditions and behavior patterns of humans. To address this problem, we propose
a generic distributionally robust model for semi-supervised learning on
distributionally shifted data. Considering both the discrepancy and the
consistency between the labeled data and the unlabeled data, we learn the
latent features that reduce person-specific discrepancy and preserve
task-specific consistency. We evaluate our model in a variety of people-centric
recognition tasks on real-world datasets, including intention recognition,
activity recognition, muscular movement recognition and gesture recognition.
The experiment results demonstrate that the proposed model outperforms the
state-of-the-art methods.Comment: 8 pages, accepted by AAAI201
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