39 research outputs found
Localization with non-Hermitian off-diagonal disorder
In this work we discuss a non-Hermitian system described via a
one-dimensional single-particle tight-binding model, where the non-Hermiticity
is governed by a random nearest-neighbor tunnellings, such that the
left-to-right and right-to-left hopping strengths are unequal. A physical
situation of completely real eigenspectrum arises owing to the Hamiltonian's
tridiagonal matrix structure under a simple \emph {sign conservation} of the
product of the conjugate nearest-neighbor tunnelling terms. The off-diagonal
disorder leads the non-Hermitian system to a localization-delocalization
transition. The emergent nature of the transition is recognized through a
finite-size spectral analysis. A comprehensive scaling theorem is then
developed for characterizing the criticality. We perform careful analysis of
localization length, inverse participation ratio, and energy splitting for
reporting the scaling exponents, which turns out to be different from the ones
in the conventional Anderson localization.Comment: 10 Pages, 5 Figure
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-
Trends of information backflow in disordered spin chains
We investigate the trends of information backflow associated with the
dynamics of a sub-part of a disordered spin-1/2 transverse field Heisenberg
chain for different regimes of the Hamiltonian. Towards this aim, the decay
profile of bipartite entanglement shared between a probe-qubit and a
system-qubit (sub-part) of the chain is monitored in time. A clear shift in the
trends of the decay profiles of the bipartite entanglement from monotonic in
the low-disorder limit to non-monotonic in the moderately large disorder limit
occurs due to strong information backflow from the environment
(complementary-part) to the system-qubit. A connection between environmental
interruption caused by the information backflow and the disorder strength is
established by examining the entanglement revival frequencies. The growth
patterns of the revival frequencies in the localized phase play an instrumental
role to effectively distinguish an interacting system (many-body localized)
from its non-interacting (Anderson localized) counterpart.Comment: 7 pages, 4 figures, close to the published versio