4,041 research outputs found
Entanglement of quantum spin systems: a valence-bond approach
In order to quantify entanglement between two parts of a quantum system, one
of the most used estimator is the Von Neumann entropy. Unfortunately, computing
this quantity for large interacting quantum spin systems remains an open issue.
Faced with this difficulty, other estimators have been proposed to measure
entanglement efficiently, mostly by using simulations in the valence-bond
basis. We review the different proposals and try to clarify the connections
between their geometric definitions and proper observables. We illustrate this
analysis with new results of entanglement properties of spin 1 chains.Comment: Proceedings of StatPhys 24 satellite conference in Hanoi; submitted
for a special issue of Modern Physics Letters
Valence bond entanglement entropy of frustrated spin chains
We extend the definition of the recently introduced valence bond entanglement
entropy to arbitrary SU(2) wave functions of S=1/2 spin systems. Thanks to a
reformulation of this entanglement measure in terms of a projection, we are
able to compute it with various numerical techniques for frustrated spin
models. We provide extensive numerical data for the one-dimensional J1-J2 spin
chain where we are able to locate the quantum phase transition by using the
scaling of this entropy with the block size. We also systematically compare
with the scaling of the von Neumann entanglement entropy. We finally underline
that the valence-bond entropy definition does depend on the choice of
bipartition so that, for frustrated models, a "good" bipartition should be
chosen, for instance according to the Marshall sign.Comment: 10 pages, 6 figures; v2: published versio
Melonic phase transition in group field theory
Group field theories have recently been shown to admit a 1/N expansion
dominated by so-called `melonic graphs', dual to triangulated spheres. In this
note, we deepen the analysis of this melonic sector. We obtain a combinatorial
formula for the melonic amplitudes in terms of a graph polynomial related to a
higher dimensional generalization of the Kirchhoff tree-matrix theorem. Simple
bounds on these amplitudes show the existence of a phase transition driven by
melonic interaction processes. We restrict our study to the Boulatov-Ooguri
models, which describe topological BF theories and are the basis for the
construction of four dimensional models of quantum gravity.Comment: 8 pages, 4 figures; to appear in Letters in Mathematical Physic
Measurement of the linear thermo-optical coefficient of GaInP using photonic crystal nanocavities
GaInP is a promising candidate for thermally tunable
nanophotonic devices due to its low thermal conductivity. In this work we study
its thermo-optical response. We obtain the linear thermo-optical coefficient
by investigating the transmission
properties of a single mode-gap photonic crystal nanocavity.Comment: 7 pages, 4 figure
Tuning out disorder-induced localization in nanophotonic cavity arrays
Weakly coupled high-Q nanophotonic cavities are building blocks of slow-light
waveguides and other nanophotonic devices. Their functionality critically
depends on tuning as resonance frequencies should stay within the bandwidth of
the device. Unavoidable disorder leads to random frequency shifts which cause
localization of the light in single cavities. We present a new method to finely
tune individual resonances of light in a system of coupled nanocavities. We use
holographic laser-induced heating and address thermal crosstalk between
nanocavities using a response matrix approach. As a main result we observe a
simultaneous anticrossing of 3 nanophotonic resonances, which were initially
split by disorder.Comment: 11 page
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