77 research outputs found
Simulation of anyons with tensor network algorithms
Interacting systems of anyons pose a unique challenge to condensed matter
simulations due to their non-trivial exchange statistics. These systems are of
great interest as they have the potential for robust universal quantum
computation, but numerical tools for studying them are as yet limited. We show
how existing tensor network algorithms may be adapted for use with systems of
anyons, and demonstrate this process for the 1-D Multi-scale Entanglement
Renormalisation Ansatz (MERA). We apply the MERA to infinite chains of
interacting Fibonacci anyons, computing their scaling dimensions and local
scaling operators. The scaling dimensions obtained are seen to be in agreement
with conformal field theory. The techniques developed are applicable to any
tensor network algorithm, and the ability to adapt these ansaetze for use on
anyonic systems opens the door for numerical simulation of large systems of
free and interacting anyons in one and two dimensions.Comment: Fixed typos, matches published version. 16 pages, 21 figures, 4
tables, RevTeX 4-1. For a related work, see arXiv:1006.247
Magnetization of SrCu2(BO3)2 in ultrahigh magnetic fields up to 118 T
The magnetization process of the orthogonal-dimer antiferromagnet SrCu2(BO3)2
is investigated in high magnetic fields of up to 118 T. A 1/2 plateau is
clearly observed in the field range 84 to 108 T in addition to 1/8, 1/4 and 1/3
plateaux at lower fields. Using a combination of state-of-the-art numerical
simulations, the main features of the high-field magnetization, a 1/2 plateau
of width 24 T, a 1/3 plateau of width 34 T, and no 2/5 plateau, are shown to
agree quantitatively with the Shastry-Sutherland model if the ratio of inter-
to intra-dimer exchange interactions J'/J=0.63. It is further predicted that
the intermediate phase between the 1/3 and 1/2 plateau is not uniform but
consists of a 1/3 supersolid followed by a 2/5 supersolid and possibly a
domain-wall phase, with a reentrance into the 1/3 supersolid above the 1/2
plateau.Comment: 5 pages + 10 pages supplemental materia
Entanglement Entropy of Random Fractional Quantum Hall Systems
The entanglement entropy of the and quantum Hall
states in the presence of short range random disorder has been calculated by
direct diagonalization. A microscopic model of electron-electron interaction is
used, electrons are confined to a single Landau level and interact with long
range Coulomb interaction. For very weak disorder, the values of the
topological entanglement entropy are roughly consistent with expected
theoretical results. By considering a broader range of disorder strengths, the
fluctuation in the entanglement entropy was studied in an effort to detect
quantum phase transitions. In particular, there is a clear signature of a
transition as a function of the disorder strength for the state.
Prospects for using the density matrix renormalization group to compute the
entanglement entropy for larger system sizes are discussed.Comment: 29 pages, 16 figures; fixed figures and figure captions; revised
fluctuation calculation
Binding of a 3He impurity to a screw dislocation in solid 4He
Using first-principle simulations for the probability density of finding a
3He atom in the vicinity of the screw dislocation in solid 4He, we determine
the binding energy to the dislocation nucleus E_B = 0.8 \pm 0.1 K and the
density of localized states at larger distances. The specific heat due to 3He
features a peak similar to the one observed in recent experiments, and our
model can also account for the observed increase in shear modulus at low
temperature. We further discuss the role of 3He in the picture of superfluid
defects.Comment: 4 pages, 4 figure
Entanglement renormalization and boundary critical phenomena
The multiscale entanglement renormalization ansatz is applied to the study of
boundary critical phenomena. We compute averages of local operators as a
function of the distance from the boundary and the surface contribution to the
ground state energy. Furthermore, assuming a uniform tensor structure, we show
that the multiscale entanglement renormalization ansatz implies an exact
relation between bulk and boundary critical exponents known to exist for
boundary critical systems.Comment: 6 pages, 4 figures; for a related work see arXiv:0912.164
Thin helium film on a glass substrate
We investigate by Monte Carlo simulations the structure, energetics and
superfluid properties of thin helium-four films (up to four layers) on a glass
substrate, at low temperature. The first adsorbed layer is found to be solid
and "inert", i.e., atoms are localized and do not participate to quantum
exchanges. Additional layers are liquid, with no clear layer separation above
the second one. It is found that a single helium-three impurity resides on the
outmost layer, not significantly further away from the substrate than
helium-four atoms on the same layer.Comment: Six figures, submitted for publication to the Journal of Low
Temperature Physic
Non-Fermi-liquid d-wave metal phase of strongly interacting electrons
Developing a theoretical framework for conducting electronic fluids
qualitatively distinct from those described by Landau's Fermi-liquid theory is
of central importance to many outstanding problems in condensed matter physics.
One such problem is that, above the transition temperature and near optimal
doping, high-transition-temperature copper-oxide superconductors exhibit
`strange metal' behaviour that is inconsistent with being a traditional Landau
Fermi liquid. Indeed, a microscopic theory of a strange-metal quantum phase
could shed new light on the interesting low-temperature behaviour in the
pseudogap regime and on the d-wave superconductor itself. Here we present a
theory for a specific example of a strange metal---the 'd-wave metal'. Using
variational wavefunctions, gauge theoretic arguments, and ultimately
large-scale density matrix renormalization group calculations, we show that
this remarkable quantum phase is the ground state of a reasonable microscopic
Hamiltonian---the usual t-J model with electron kinetic energy and two-spin
exchange supplemented with a frustrated electron `ring-exchange' term,
which we here examine extensively on the square lattice two-leg ladder. These
findings constitute an explicit theoretical example of a genuine
non-Fermi-liquid metal existing as the ground state of a realistic model.Comment: 22 pages, 12 figures: 6 pages, 7 figures of main text + 16 pages, 5
figures of Supplementary Information; this is approximately the version
published in Nature, minus various subedits in the main tex
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