2,180 research outputs found
Construction of spin models displaying quantum criticality from quantum field theory
We provide a method for constructing finite temperature states of
one-dimensional spin chains displaying quantum criticality. These models are
constructed using correlators of products of quantum fields and have an
analytical purification. Their properties can be investigated by Monte-Carlo
simulations, which enable us to study the low-temperature phase diagram and to
show that it displays a region of quantum criticality. The mixed states
obtained are shown to be close to the thermal state of a simple nearest
neighbour Hamiltonian.Comment: 10 pages, 6 figure
Lattice effects on Laughlin wave functions and parent Hamiltonians
We investigate lattice effects on wave functions that are lattice analogues
of bosonic and fermionic Laughlin wave functions with number of particles per
flux in the Landau levels. These wave functions are defined
analytically on lattices with particles per lattice site, where may
be different than . We give numerical evidence that these states have the
same topological properties as the corresponding continuum Laughlin states for
different values of and for different fillings . These states define,
in particular, particle-hole symmetric lattice Fractional Quantum Hall states
when the lattice is half-filled. On the square lattice it is observed that for
this particle-hole symmetric state displays the topological
properties of the continuum Laughlin state at filling fraction , while
for larger there is a transition towards long-range ordered
anti-ferromagnets. This effect does not persist if the lattice is deformed from
a square to a triangular lattice, or on the Kagome lattice, in which case the
topological properties of the state are recovered. We then show that changing
the number of particles while keeping the expression of these wave functions
identical gives rise to edge states that have the same correlations in the bulk
as the reference lattice Laughlin states but a different density at the edge.
We derive an exact parent Hamiltonian for which all these edge states are
ground states with different number of particles. In addition this Hamiltonian
admits the reference lattice Laughlin state as its unique ground state of
filling factor . Parent Hamiltonians are also derived for the lattice
Laughlin states at other fillings of the lattice, when or
and when also at half-filling.Comment: 18 pages, 15 figure
Quantum mutual information of an entangled state propagating through a fast-light medium
Although it is widely accepted that classical information cannot travel
faster than the speed of light in vacuum, the behavior of quantum correlations
and quantum information propagating through actively-pumped fast-light media
has not been studied in detail. To investigate this behavior, we send one half
of an entangled state of light through a gain-assisted fast-light medium and
detect the remaining quantum correlations. We show that the quantum
correlations can be advanced by a small fraction of the correlation time while
the entanglement is preserved even in the presence of noise added by
phase-insensitive gain. Additionally, although we observe an advance of the
peak of the quantum mutual information between the modes, we find that the
degradation of the mutual information due to the added noise appears to prevent
an advancement of the leading edge. In contrast, we show that both the leading
and trailing edges of the mutual information in a slow-light system can be
significantly delayed
Soft Lenses
A series of cases fitted with Bionite soft lenses is described. Good results were obtained in bullous keratopathy, dry eyes, early and moderately advanced Stevens-Johnson syndrome and pemphigoid, and some cases of indolent corneal ulcers. The lenses appear to be a most effective replacement for tarsorrhaphy, haptic lenses and epikeratoprostheses.S. Afr. Med. J, 47, 148 (1973
- …