1,453 research outputs found
Boundary-driven phase transitions in open two-species driven systems with an umbilic point
Different phases in open driven systems are governed by either shocks or
rarefaction waves. A presence of an isolated umbilic point in bidirectional
systems of interacting particles stabilizes an unusual large scale excitation,
an umbilic shock (U-shock). We show that in open systems the U-shock governs a
large portion of phase space, and drives a new discontinuous transition between
the two rarefaction-controlled phases. This is in contrast with strictly
hyperbolic case where such a transition is always continuous. Also, we describe
another robust phase which takes place of the phase governed by the U-shock, if
the umbilic point is not isolated.Comment: 17 pages, 6 Figs. arXiv admin note: text overlap with
arXiv:1206.1490; small typos in Eq (3),(5) correcte
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
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
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
Transition probabilities and dynamic structure factor in the ASEP conditioned on strong flux
We consider the asymmetric simple exclusion processes (ASEP) on a ring
constrained to produce an atypically large flux, or an extreme activity. Using
quantum free fermion techniques we find the time-dependent conditional
transition probabilities and the exact dynamical structure factor under such
conditioned dynamics. In the thermodynamic limit we obtain the explicit scaling
form. This gives a direct proof that the dynamical exponent in the extreme
current regime is rather than the KPZ exponent which
characterizes the ASEP in the regime of typical currents. Some of our results
extend to the activity in the partially asymmetric simple exclusion process,
including the symmetric case.Comment: 16 pages, 2 figure
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
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