126 research outputs found
Finite-size scaling exponents and entanglement in the two-level BCS model
We analyze the finite-size properties of the two-level BCS model. Using the
continuous unitary transformation technique, we show that nontrivial scaling
exponents arise at the quantum critical point for various observables such as
the magnetization or the spin-spin correlation functions. We also discuss the
entanglement properties of the ground state through the concurrence which
appears to be singular at the transition.Comment: 4 pages, 3 figures, published versio
Finite-Size Scaling Exponents of the Lipkin-Meshkov-Glick Model
We study the ground state properties of the critical Lipkin-Meshkov-Glick
model. Using the Holstein-Primakoff boson representation, and the continuous
unitary transformation technique, we compute explicitly the finite-size scaling
exponents for the energy gap, the ground state energy, the magnetization, and
the spin-spin correlation functions. Finally, we discuss the behavior of the
two-spin entanglement in the vicinity of the phase transition.Comment: 4 pages, published versio
Creation and Manipulation of Anyons in the Kitaev Model
We analyze the effect of local spin operators in the Kitaev model on the
honeycomb lattice. We show, in perturbation around the isolated-dimer limit,
that they create Abelian anyons together with fermionic excitations which are
likely to play a role in experiments. We derive the explicit form of the
operators creating and moving Abelian anyons without creating fermions and show
that it involves multi-spin operations. Finally, the important experimental
constraints stemming from our results are discussed.Comment: 4 pages, 3 figures, published versio
Quantum phase transitions in fully connected spin models: an entanglement perspective
We consider a set of fully connected spins models that display first- or
second-order transitions and for which we compute the ground-state entanglement
in the thermodynamical limit. We analyze several entanglement measures
(concurrence, R\'enyi entropy, and negativity), and show that, in general,
discontinuous transitions lead to a jump of these quantities at the transition
point. Interestingly, we also find examples where this is not the case.Comment: 9 pages, 7 figures, published versio
Geometric Phase and Quantum Phase Transition in the Lipkin-Meshkov-Glick model
The relation between the geometric phase and quantum phase transition has
been discussed in the Lipkin-Meshkov-Glick model. Our calculation shows the
ability of geometric phase of the ground state to mark quantum phase transition
in this model. The possibility of the geometric phase or its derivatives as the
universal order parameter of characterizing quantum phase transitions has been
also discussed.Comment: 6 pages and to be published in Phys.Lett.
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