47 research outputs found
Pairwise Quantum Correlations for Superpositions of Dicke States
Pairwise correlation is really an important property for multi-qubit states.
For the two-qubit X states extracted from Dicke states and their superposition
states, we obtain a compact expression of the quantum discord by numerical
check. We then apply the expression to discuss the quantum correlation of the
reduced two-qubit states of Dicke states and their superpositions, and the
results are compared with those obtained by entanglement of formation, which is
a quantum entanglement measure.Comment: 17pages, 8 figures,slightly improved and slightly extended
version,and added some reference
Reduced fidelity approach for quantum phase transitions in spin-1/2 dimerized Heisenberg chains
We use reduced fidelity approach to characterize quantum phase transitions in
the one-dimensional spin-1/2 dimerized Heisenberg chain in the
antiferromagnetic case. The reduced fidelity susceptibilities between two
nearest-neighboring spin pairs are considered. We find that they are directly
related to the square of the second derivative of the ground-state energy. This
enables us to conclude that the former might be a more effective indicator of
the second-order quantum phase transitions than the latter. Two further
exemplifications are given to confirm the conclusion is available for a broad
class of systems with SU(2) and translation symmetries. Moreover, a general
connection between reduced fidelity susceptibility and quantum phase
transitions is illustrated.Comment: 6 pages, 2 figure
Reduced fidelity susceptibility and its finite-size scaling behaviors
We derive a general formula of the reduced fidelity susceptibility when the
reduced density matrix is block-diagonal. By using this result and
the continuous unitary transformations, we study finite-size scaling of the
reduced fidelity susceptibility in the Lipkin-Meshkov-Glick Model. It is found
that it can be used to characterize quantum phase transitions, implying that we
can extract information of quantum phase transitions only from the fidelity of
a subsystem, which is of practical meaning in experiments.Comment: 7 pages, 3 figure