48 research outputs found
Entanglement Echoes in Quantum Computation
We study the stability of entanglement in a quantum computer implementing an
efficient quantum algorithm, which simulates a quantum chaotic dynamics. For
this purpose, we perform a forward-backward evolution of an initial state in
which two qubits are in a maximally entangled Bell state. If the dynamics is
reversed after an evolution time , there is an echo of the entanglement
between these two qubits at time . Perturbations attenuate the
pairwise entanglement echo and generate entanglement between these two qubits
and the other qubits of the quantum computer.Comment: 4 pages, 4 figure
Negative differential conductivity in far-from-equilibrium quantum spin chains
We show that, when a finite anisotropic Heisenberg spin-1/2 chain in the
gapped regime is driven far from equilibrium, oppositely polarized
ferromagnetic domains build up at the edges of the chain, thus suppressing
quantum spin transport. As a consequence, a negative differential conductivity
regime arises, where increasing the driving decreases the current. The above
results are explained in terms of magnon localization and are shown to be
structurally stable against breaking of integrability.Comment: 5 pages, 4 figures. Published versio
Classical versus quantum errors in quantum computation of dynamical systems
We analyze the stability of a quantum algorithm simulating the quantum
dynamics of a system with different regimes, ranging from global chaos to
integrability. We compare, in these different regimes, the behavior of the
fidelity of quantum motion when the system's parameters are perturbed or when
there are unitary errors in the quantum gates implementing the quantum
algorithm. While the first kind of errors has a classical limit, the second one
has no classical analogue. It is shown that, whereas in the first case
(``classical errors'') the decay of fidelity is very sensitive to the dynamical
regime, in the second case (``quantum errors'') it is almost independent of the
dynamical behavior of the simulated system. Therefore, the rich variety of
behaviors found in the study of the stability of quantum motion under
``classical'' perturbations has no correspondence in the fidelity of quantum
computation under its natural perturbations. In particular, in this latter case
it is not possible to recover the semiclassical regime in which the fidelity
decays with a rate given by the classical Lyapunov exponent.Comment: 8 pages, 7 figure
Thermalization and ergodicity in many-body open quantum systems
We study thermalization in many-body quantum systems locally coupled to an
external bath. It is shown that quantum chaotic systems do thermalize, that is,
they exhibit relaxation to an invariant ergodic state which, in the bulk, is
well approximated by the grand canonical state. Moreover, the resulting ergodic
state in the bulk does not depend on the details of the baths. On the other
hand, for integrable systems the invariant state does depend on the bath and is
different from the grand canonical state.Comment: 4 pages, 4 figures; v2. one new figur
Conservative chaotic map as a model of quantum many-body environment
We study the dynamics of the entanglement between two qubits coupled to a
common chaotic environment, described by the quantum kicked rotator model. We
show that the kicked rotator, which is a single-particle deterministic
dynamical system, can reproduce the effects of a pure dephasing many-body bath.
Indeed, in the semiclassical limit the interaction with the kicked rotator can
be described as a random phase-kick, so that decoherence is induced in the
two-qubit system. We also show that our model can efficiently simulate
non-Markovian environments.Comment: 8 pages, 4 figure
Charge and spin transport in strongly correlated one-dimensional quantum systems driven far from equilibrium
We study the charge conductivity in one-dimensional prototype models of
interacting particles, such as the Hubbard and the t-V spinless fermion model,
when coupled to some external baths injecting and extracting particles at the
boundaries. We show that, if these systems are driven far from equilibrium, a
negative differential conductivity regime can arise. The above electronic
models can be mapped into Heisenberg-like spin ladders coupled to two magnetic
baths, so that charge transport mechanisms are explained in terms of quantum
spin transport. The negative differential conductivity is due to oppositely
polarized ferromagnetic domains which arise at the edges of the chain, and
therefore inhibit spin transport: we propose a qualitative understanding of the
phenomenon by analyzing the localization of one-magnon excitations created at
the borders of a ferromagnetic region. We also show that negative differential
conductivity is stable against breaking of integrability. Numerical simulations
of non-equilibrium time evolution have been performed by employing a
Monte-Carlo wave function approach and a matrix product operator formalism.Comment: 20 pages, 19 figures. Published versio
Rheological Characterization of Ethylcellulose-Based Melts for Pharmaceutical Applications
Rheological characterization of ethylcellulose (EC)-based melts intended for the production, via micro-injection moulding (μIM), of oral capsular devices for prolonged release was carried out. Neat EC, plasticized EC and plasticized EC containing solid particles of a release modifier (filler volume content in the melt around 30%) were examined by capillary and rotational rheometry tests. Two release modifiers, differing in both chemical nature and particle geometry, were investigated. When studied by capillary rheometry, neat EC appeared at process temperatures as a highly viscous melt with a shear-thinning characteristic that progressively diminished as the apparent shear rate increased. Thus, EC as such could not successfully be processed via μIM. Plasticization, which induces changes in the material microstructure, enhanced the shear-thinning characteristic of the melt and reduced considerably its elastic properties. Marked wall slip effects were noticed in the capillary flow of the plasticized EC-based melts, with or without release modifier particles. The presence of these particles brought about an increase in viscosity, clearly highlighted by the dynamic experiments at the rotational rheometer. However, it did not impair the material processability. The thermal and rheological study undertaken would turn out a valid guideline for the development of polymeric materials based on pharma-grade polymers with potential for new pharmaceutical applications of μIM
Bacterial Communities in the Embryo of Maize Landraces:Relation with Susceptibility to Fusarium Ear Rot
Locally adapted maize accessions (landraces) represent an untapped resource of nutritional and resistance traits for breeding, including the shaping of distinct microbiota. Our study focused on five different maize landraces and a reference commercial hybrid, showing different susceptibility to fusarium ear rot, and whether this trait could be related to particular compositions of the bacterial microbiota in the embryo, using different approaches. Our cultivation-independent approach utilized the metabarcoding of a portion of the 16S rRNA gene to study bacterial populations in these samples. Multivariate statistical analyses indicated that the microbiota of the embryos of the accessions grouped in two different clusters: one comprising three landraces and the hybrid, one including the remaining two landraces, which showed a lower susceptibility to fusarium ear rot in field. The main discriminant between these clusters was the frequency of Firmicutes, higher in the second cluster, and this abundance was confirmed by quantification through digital PCR. The cultivation-dependent approach allowed the isolation of 70 bacterial strains, mostly Firmicutes. In vivo assays allowed the identification of five candidate biocontrol strains against fusarium ear rot. Our data revealed novel insights into the role of the maize embryo microbiota and set the stage for further studies aimed at integrating this knowledge into plant breeding programs