SciPost Phys. 13, 060 (2022) ·
published 21 September 2022
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We study a generalized quantum spin ladder with staggered long range
interactions that decay as a power-law with exponent $\alpha$. Using large
scale quantum Monte Carlo (QMC) and density matrix renormalization group (DMRG)
simulations, we show that this model undergoes a transition from a rung-dimer
phase characterized by a non-local string order parameter, to a symmetry broken
N\'eel phase. We find evidence that the transition is second order. In the
magnetically ordered phase, the spectrum exhibits gapless modes, while
excitations in the gapped phase are well described in terms of triplons --
bound states of spinons across the legs. We obtain the momentum resolved spin
dynamic structure factor numerically and find a well defined triplon band that
evolves into a gapless magnon dispersion across the transition. We further
discuss the possibility of deconfined criticality in this model.
SciPost Phys. 7, 020 (2019) ·
published 9 August 2019
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We present a major update to QuSpin, SciPostPhys.2.1.003 -- an open-source
Python package for exact diagonalization and quantum dynamics of arbitrary
boson, fermion and spin many-body systems, supporting the use of various
(user-defined) symmetries in one and higher dimension and (imaginary) time
evolution following a user-specified driving protocol. We explain how to use
the new features of QuSpin using seven detailed examples of various complexity:
(i) the transverse-field Ising chain and the Jordan-Wigner transformation, (ii)
free particle systems: the Su-Schrieffer-Heeger (SSH) model, (iii) the
many-body localized 1D Fermi-Hubbard model, (iv) the Bose-Hubbard model in a
ladder geometry, (v) nonlinear (imaginary) time evolution and the
Gross-Pitaevskii equation on a 1D lattice, (vi) integrability breaking and
thermalizing dynamics in the translationally-invariant 2D transverse-field
Ising model, and (vii) out-of-equilibrium Bose-Fermi mixtures. This easily
accessible and user-friendly package can serve various purposes, including
educational and cutting-edge experimental and theoretical research. The
complete package documentation is available under
http://weinbe58.github.io/QuSpin/index.html.
SciPost Phys. 2, 003 (2017) ·
published 13 February 2017
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We present a new open-source Python package for exact diagonalization and
quantum dynamics of spin(-photon) chains, called QuSpin, supporting the use of
various symmetries in 1-dimension and (imaginary) time evolution for chains up
to 32 sites in length. The package is well-suited to study, among others,
quantum quenches at finite and infinite times, the Eigenstate Thermalisation
hypothesis, many-body localisation and other dynamical phase transitions,
periodically-driven (Floquet) systems, adiabatic and counter-diabatic ramps,
and spin-photon interactions. Moreover, QuSpin's user-friendly interface can
easily be used in combination with other Python packages which makes it
amenable to a high-level customisation. We explain how to use QuSpin using four
detailed examples: (i) Standard exact diagonalisation of XXZ chain (ii)
adiabatic ramping of parameters in the many-body localised XXZ model, (iii)
heating in the periodically-driven transverse-field Ising model in a parallel
field, and (iv) quantised light-atom interactions: recovering the
periodically-driven atom in the semi-classical limit of a static Hamiltonian.
Dr Weinberg: "We thank Referee 3 for careful..."
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