79 research outputs found
Logarithmic divergence of the block entanglement entropy for the ferromagnetic Heisenberg model
Recent studies have shown that logarithmic divergence of entanglement entropy
as function of size of a subsystem is a signature of criticality in quantum
models. We demonstrate that the ground state entanglement entropy of sites
for ferromagnetic Heisenberg spin-1/2 chain of the length in a sector with
fixed magnetization per site grows as ,
where Comment: 4 pages, 2 fig
Manipulating energy and spin currents in nonequilibrium systems of interacting qubits
We consider generic interacting chain of qubits, which are coupled at the
edges to baths of fixed polarizations. We can determine the nonequilibrium
steady states, described by the fixed point of the Lindblad Master Equation.
Under rather general assumptions about local pumping and interactions,
symmetries of the reduced density matrix are revealed. The symmetries
drastically restrict the form of the steady density matrices in such a way that
an exponentially large subset of one--point and many--point correlation
functions are found to vanish. As an example we show how in a Heisenberg spin
chain a suitable choice of the baths can completely switch off either the spin
or the energy current, or both of them, despite the presence of large boundary
gradients.Comment: 8 pages, 3 Figure
Obtaining pure steady states in nonequilibrium quantum systems with strong dissipative couplings
Dissipative preparation of a pure steady state usually involves a commutative
action of a coherent and a dissipative dynamics on the target state. Namely,
the target pure state is an eigenstate of both the coherent and dissipative
parts of the dynamics. We show that working in the Zeno regime, i.e. for
infinitely large dissipative coupling, one can generate a pure state by a non
commutative action, in the above sense, of the coherent and dissipative
dynamics. A corresponding Zeno regime pureness criterion is derived. We
illustrate the approach, looking at both its theoretical and applicative
aspects, in the example case of an open spin- chain, driven out of
equilibrium by boundary reservoirs targeting different spin orientations. Using
our criterion, we find two families of pure nonequilibrium steady states, in
the Zeno regime, and calculate the dissipative strengths effectively needed to
generate steady states which are almost indistinguishable from the target pure
states.Comment: 8 pages, 6 figure
Infinitely dimensional Lax structure for one-dimensional Hubbard model
We report a two-parametric irreducible infinitely dimensional representation
of the Lax integrability condition for the fermi Hubbard chain. Besides being
of fundamental interest, hinting on possible novel quantum symmetry of the
model, our construction allows for an explicit representation of an exact
steady state many-body density operator for non-equilibrium boundary-driven
Hubbard chain with arbitrary (asymmetric) particle source/sink rates at the
letf/right end of the chain and with arbitrary boundary values of chemical
potentials.Comment: 5 pages in RevTex, 1 figure, version as accepted by Phys. Rev. Let
Solution of the Lindblad equation for spin helix states
Using Lindblad dynamics we study quantum spin systems with dissipative
boundary dynamics that generate a stationary nonequilibrium state with a
non-vanishing spin current that is locally conserved except at the boundaries.
We demonstrate that with suitably chosen boundary target states one can solve
the many-body Lindblad equation exactly in any dimension. As solution we obtain
pure states at any finite value of the dissipation strength and any system
size. They are characterized by a helical stationary magnetization profile and
a superdiffusive ballistic current of order one, independent of system size
even when the quantum spin system is not integrable. These results are derived
in explicit form for the one-dimensional spin-1/2 Heisenberg chain and its
higher-spin generalizations (which include for spin-1 the integrable
Zamolodchikov-Fateev model and the bi-quadratic Heisenberg chain). The
extension of the results to higher dimensions is straightforward.Comment: 23 pages, 2 figure
Inhomogeneous MPA and exact steady states of boundary driven spin chains at large dissipation
We find novel site-dependent Lax operators in terms of which we demonstrate
exact solvability of a dissipatively driven XYZ spin-1/2 chain in the Zeno
limit of strong dissipation, with jump operators polarizing the boundary spins
in arbitrary directions. We write the corresponding nonequilibrium steady state
using an inhomogeneous MPA, where the constituent matrices satisfy a simple set
of linear recurrence relations. Although these matrices can be embedded into an
infinite-dimensional auxiliary space, we have verified that they cannot be
simultaneously put into a tridiagonal form, not even in the case of axially
symmetric (XXZ) bulk interactions and general nonlongitudinal boundary
dissipation. We expect our results to have further fundamental applications for
the construction of nonlocal integrals of motion for the open XYZ model with
arbitrary boundary fields, or the eight-vertex model.Comment: 12 pages, 3 figure
Non-KPZ modes in two-species driven diffusive systems
Using mode coupling theory and dynamical Monte-Carlo simulations we
investigate the scaling behaviour of the dynamical structure function of a
two-species asymmetric simple exclusion process, consisting of two coupled
single-lane asymmetric simple exclusion processes. We demonstrate the
appearence of a superdiffusive mode with dynamical exponent in the
density fluctuations, along with a KPZ mode with and argue that this
phenomenon is generic for short-ranged driven diffusive systems with more than
one conserved density. When the dynamics is symmetric under the interchange of
the two lanes a diffusive mode with appears instead of the non-KPZ
superdiffusive mode.Comment: 5 pages, 7 figure
Dynamic phase transitions in electromigration-induced step bunching
Electromigration-induced step bunching in the presence of sublimation or
deposition is studied theoretically in the attachment-limited regime. We
predict a phase transition as a function of the relative strength of kinetic
asymmetry and step drift. For weak asymmetry the number of steps between
bunches grows logarithmically with bunch size, whereas for strong asymmetry at
most a single step crosses between two bunches. In the latter phase the
emission and absorption of steps is a collective process which sets in only
above a critical bunch size and/or step interaction strength.Comment: 4 pages, 4 figure
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