169 research outputs found
Quantum Phase Transitions and Matrix Product States in Spin Ladders
We investigate quantum phase transitions in ladders of spin 1/2 particles by
engineering suitable matrix product states for these ladders. We take into
account both discrete and continuous symmetries and provide general classes of
such models. We also study the behavior of entanglement of different
neighboring sites near the transition point and show that quantum phase
transitions in these systems are accompanied by divergences in derivatives of
entanglement.Comment: 20 pages, 6 figures, essential changes (i.e derivation of the
Hamiltonian), Revte
Matrix product states and exactly solvable spin 1/2 Heisenberg chains with nearest neighbor interactions
Using the matrix product formalism, we introduce a two parameter family of
exactly solvable spin 1/2 Heisenberg chains in magnetic field (with
nearest neighbor interactions) and calculate the ground state and correlation
functions in compact form. The ground state has a very interesting property:
all the pairs of spins are equally entangled with each other. Therefore it is
possible to engineer long-range entanglement in experimentally realizable spin
systems on the one hand and study more closely quantum phase transition in such
systems on the other.Comment: 4 pages, RevTex, references added, improved presentation, typos fixe
A new family of matrix product states with Dzyaloshinski-Moriya interactions
We define a new family of matrix product states which are exact ground states
of spin 1/2 Hamiltonians on one dimensional lattices. This class of
Hamiltonians contain both Heisenberg and Dzyaloshinskii-Moriya interactions but
at specified and not arbitrary couplings. We also compute in closed forms the
one and two-point functions and the explicit form of the ground state. The
degeneracy structure of the ground state is also discussed.Comment: 15 pages, 1 figur
Quadratic operators used in deducing exact ground states for correlated systems: ferromagnetism at half filling provided by a dispersive band
Quadratic operators are used in transforming the model Hamiltonian (H) of one
correlated and dispersive band in an unique positive semidefinite form coopting
both the kinetic and interacting part of H. The expression is used in deducing
exact ground states which are minimum energy eigenstates only of the full
Hamiltonian. It is shown in this frame that at half filling, also dispersive
bands can provide ferromagnetism in exact terms by correlation effects .Comment: 7 page
Evolutionary implications of microplastics for soil biota
This is the author accepted manuscript. The final version is available from CSIRO Publishing via the DOI in this recordMicroplastic pollution is increasingly considered to be a factor of global change: in addition to aquatic ecosystems, this persistent contaminant is also found in terrestrial systems and soils. Microplastics have been chiefly examined in soils in terms of the presence and potential effects on soil biota. Given the persistence and widespread distribution of microplastics, it is also important to consider potential evolutionary implications of the presence of microplastics in soil; we offer such a perspective for soil microbiota. We discuss the range of selection pressures likely to act upon soil microbes, highlight approaches for the study of evolutionary responses to microplastics, and present the obstacles to be overcome. Pondering the evolutionary consequences of microplastics in soils can yield new insights into the effects of this group of pollutants, including establishing ‘true’ baselines in soil ecology, and understanding future responses of soil microbial populations and communities.MR acknowledges support from the ERC Advanced Grant ‘Gradual Change’ (694368).
UK received funding from the European Union's Horizon 2020 research and innovation
program under Marie Skłodowska-Curie grant agreement no. 751699
Random Spin-1 Quantum Chains
We study disordered spin-1 quantum chains with random exchange and
biquadratic interactions using a real space renormalization group approach. We
find that the dimerized phase of the pure biquadratic model is unstable and
gives rise to a random singlet phase in the presence of weak disorder. In the
Haldane region of the phase diagram we obtain a quite different behavior.Comment: 13 pages, Latex, no figures, to be published in Solid State
Communication
Introduction to Quantum Integrability
In this article we review the basic concepts regarding quantum integrability.
Special emphasis is given on the algebraic content of integrable models. The
associated algebras are essentially described by the Yang-Baxter and boundary
Yang-Baxter equations depending on the choice of boundary conditions. The
relation between the aforementioned equations and the braid group is briefly
discussed. A short review on quantum groups as well as the quantum inverse
scattering method (algebraic Bethe ansatz) is also presented.Comment: 56 pages, Latex. A few typos correcte
Implementation of Spin Hamiltonians in Optical Lattices
We propose an optical lattice setup to investigate spin chains and ladders.
Electric and magnetic fields allow us to vary at will the coupling constants,
producing a variety of quantum phases including the Haldane phase, critical
phases, quantum dimers etc. Numerical simulations are presented showing how
ground states can be prepared adiabatically. We also propose ways to measure a
number of observables, like energy gap, staggered magnetization, end-chain
spins effects, spin correlations and the string order parameter
Entanglement study of the 1D Ising model with Added Dzyaloshinsky-Moriya interaction
We have studied occurrence of quantum phase transition in the one-dimensional
spin-1/2 Ising model with added Dzyaloshinsky-Moriya (DM) interaction from bi-
partite and multi-partite entanglement point of view. Using exact numerical
solutions, we are able to study such systems up to 24 qubits. The minimum of
the entanglement ratio R \tau 2/\tau 1 < 1, as a novel estimator of
QPT, has been used to detect QPT and our calculations have shown that its
minimum took place at the critical point. We have also shown both the
global-entanglement (GE) and multipartite entanglement (ME) are maximal at the
critical point for the Ising chain with added DM interaction. Using matrix
product state approach, we have calculated the tangle and concurrence of the
model and it is able to capture and confirm our numerical experiment result.
Lack of inversion symmetry in the presence of DM interaction stimulated us to
study entanglement of three qubits in symmetric and antisymmetric way which
brings some surprising results.Comment: 18 pages, 9 figures, submitte
Nonlinear integral equations for finite volume excited state energies of the O(3) and O(4) nonlinear sigma-models
We propose nonlinear integral equations for the finite volume one-particle
energies in the O(3) and O(4) nonlinear sigma-models. The equations are written
in terms of a finite number of components and are therefore easier to solve
numerically than the infinite component excited state TBA equations proposed
earlier. Results of numerical calculations based on the nonlinear integral
equations and the excited state TBA equations agree within numerical precision.Comment: numerical results adde
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