44,433 research outputs found
Manipulation of the dynamics of many-body systems via quantum control methods
We investigate how dynamical decoupling methods may be used to manipulate the
time evolution of quantum many-body systems. These methods consist of sequences
of external control operations designed to induce a desired dynamics. The
systems considered for the analysis are one-dimensional spin-1/2 models, which,
according to the parameters of the Hamiltonian, may be in the integrable or
non-integrable limits, and in the gapped or gapless phases. We show that an
appropriate control sequence may lead a chaotic chain to evolve as an
integrable chain and a system in the gapless phase to behave as a system in the
gapped phase. A key ingredient for the control schemes developed here is the
possibility to use, in the same sequence, different time intervals between
control operations.Comment: 10 pages, 3 figure
Delocalization and wave-packet dynamics in one-dimensional diluted Anderson models
We study the nature of one-electron eigen-states in a one-dimensional diluted
Anderson model where every Anderson impurity is diluted by a periodic function
. Using renormalization group and transfer matrix techniques, we provide
accurate estimates of the extended states which appear in this model, whose
number depends on the symmetry of the diluting function . The density of
states (DOS) for this model is also numerically obtained and its main features
are related to the symmetries of the diluting function . Further, we show
that the emergence of extended states promotes a sub-diffusive spread of an
initially localized wave-packet.Comment: 6 pages, 6 figures, to appear in EPJ
Updating constraints on phantom crossing gravity
We establish constraints on gravity by considering the possibility of
a scenario that supports a phantom crossing of the equation of state parameter
. After determining the viable parameter space of the model, while
checking the impact on the background dynamics, we perform an analysis to
obtain constraints on cosmological parameters and determine the viability of
this scenario. To this end, we use combined data sets from cosmic chronometers
(CC), baryonic acoustic oscillations (BAO), redshift space distortion (RSD) and
Type Ia supernovae (SN) measurements from the latest Pantheon set, in which
the impact on the absolute magnitude due to the change of the effective
gravitational constant is also considered. It is found that a state where a
phantom crossing of happens is favored by data, and the
model is competitive with the CDM one by statistical criteria, such as
AIC and BIC. Additionally, we find evidence of the Hubble tension being
alleviated within the model, at the same time that it does not worsen
the growth one, indicating a possibility of the present scenario as an option
to address the current cosmic tensions.Comment: 18 pages, 6 figures, 2 tables. Updated results and references;
published in JCA
Many-particle confinement by constructed disorder and quantum computing
Many-particle confinement (localization) is studied for a 1D system of
spinless fermions with nearest-neighbor hopping and interaction, or
equivalently, for an anisotropic Heisenberg spin-1/2 chain. This system is
frequently used to model quantum computers with perpetually coupled qubits. We
construct a bounded sequence of site energies that leads to strong
single-particle confinement of all states on individual sites. We show that
this sequence also leads to a confinement of all many-particle states in an
infinite system for a time that scales as a high power of the reciprocal
hopping integral. The confinement is achieved for strong interaction between
the particles while keeping the overall bandwidth of site energies
comparatively small. The results show viability of quantum computing with
time-independent qubit coupling.Comment: An invited paper for the topical issue of J. Opt. B on quantum
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