60 research outputs found
Spontaneous magnetization of quantum spin model in joint presence of quenched and annealed disorder
We investigate equilibrium statistical properties of the quantum XY spin-1/2
model in an external magnetic field when the interaction and field parts are
subjected to quenched or/and annealed disorder. The randomness present in the
system are termed annealed or quenched depending on the relation between two
different time scales - the time scale associated with the equilibriation of
the randomness and the time of observation. Within a mean-field framework, we
study the effects of disorders on spontaneous magnetization, both by
perturbative and numerical techniques. Our primary interest is to understand
the differences between quenched and annealed cases, and also to investigate
the interplay when both of them are present in a system. We observe in
particular that when interaction and field terms are respectively quenched and
annealed, critical temperature for the system to magnetize in the direction
parallel to the applied field does not depend on any of the disorders. Further,
an annealed disordered interaction neither affects the magnetizations nor the
critical temperatures. We carry out a comparative study of the different
combinations of the disorders in the interaction and field terms, and point out
their generic features.Comment: 9 pages, 2 figures, 1 tabl
Adiabatic freezing of long-range quantum correlations in spin chains
We consider a process to create quasi long-range quantum discord between the
non-interacting end spins of a quantum spin chain, with the end spins weakly
coupled to the bulk of the chain. The process is not only capable of creating
long-range quantum correlation but the latter remains frozen, when certain weak
end-couplings are adiabatically varied below certain thresholds. We term this
phenomenon as adiabatic freezing of quantum correlation. We observe that the
freezing is robust to moderate thermal fluctuations and is intrinsically
related to the cooperative properties of the quantum spin chain. In particular,
we find that the energy gap of the system remains frozen for these adiabatic
variations, and moreover, considering the end spins as probes, we show that the
interval of freezing can detect the anisotropy transition in quantum XY spin
chains. Importantly, the adiabatic freezing of long-range quantum correlations
can be simulated with contemporary experimental techniques.Comment: Main text (6 pages, 6 figures) and Supplemental material (4 pages, 4
figures), REVTeX 4-
Beating no-go theorems by engineering defects in quantum spin models
There exist diverse no-go theorems, ranging from no-cloning to monogamies of
quantum correlations and Bell inequality violations, which restrict the
processing of information in the quantum world. In a multipartite scenario,
monogamy of Bell inequality violation and exclusion principle of dense coding
are such theorems, which impede the ability of the system to have quantum
advantage between all its parts. In ordered spin systems, the twin restrictions
of translation invariance and monogamy of quantum correlations, in general,
enforce the bipartite states to be neither Bell inequality violating nor
dense-codeable. We show that these quantum characteristics, viz. Bell
inequality violation and dense-codeability, can be resurrected, and thereby the
no-go theorems overcome, by having quenched disorder in the system parameters
leading to quantum spin glass or quantum random field models. We show that the
quantum characteristics are regained even though the quenched averaging keeps
the disordered spin chains translationally invariant at the physically relevant
level of observables. The results show that it is possible to conquer
constraints imposed by quantum mechanics in ordered systems by introducing
impurities.Comment: 9 pages, 6 figures, RevTeX 4.
An autopsy series of an oft-missed ante-mortem diagnosis: hemophagocytic lymphohistiocytosis
Hemophagocytic lymphohistiocytosis (HLH) is a rare and potentially fatal syndrome resulting from a hyperactivated immune system. Diverse patient profiles and clinical presentations often result in misdiagnosis. This article describes the varied clinical presentations and autopsy findings in three patients with this entity. The etiopathogenesis of HLH, its disparate and confounding clinical features, the diagnostic criteria, and management principles are also briefly reviewed
Asymptomatic levo uterine torsion of 90 degrees during caesarean section
Uterine torsion is defined as a rotation of uterus more than 45 degrees along it’s long axis. Some degree of dextrorotation in the gravid uterus can be a normal finding, however rotation greater than 45 degrees along the longitudinal axis of the uterus which is described as uterine torsion is a rare pathological condition in  obstetrical practice. We report a case of levotorsion of the uterus by 90 degrees wherein patient had presented with pre term labour at 35W5D POG and levotorsion was encountered and managed intraop during caesarean. Uterine torsion of 90 degrees was encountered with the round ligament and tubo ovarian complex along with the uterine artery lying anteriorly at the incision site and lower segment of uterus rotated laterally onto the right side. The surgery was handled diligently resulting in average blood loss. Blood loss during the surgery was average. After the delivery of the baby, uterus returned to anatomical position and levotorsion corrected spontaneously
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