1,318 research outputs found
Orbital selective crossover and Mott transitions in an asymmetric Hubbard model of cold atoms in optical lattices
We study the asymmetric Hubbard model at half-filling as a generic model to
describe the physics of two species of repulsively interacting fermionic cold
atoms in optical lattices. We use Dynamical Mean Field Theory to obtain the
paramagnetic phase diagram of the model as function of temperature, interaction
strength and hopping asymmetry. A Mott transition with a region of two
coexistent solutions is found for all nonzero values of the hopping asymmetry.
At low temperatures the metallic phase is a heavy Fermi-liquid, qualitatively
analogous to the Fermi liquid state of the symmetric Hubbard model. Above a
coherence temperature, an orbital-selective crossover takes place, wherein one
fermionic species effectively localizes, and the resulting bad metallic state
resembles the non-Fermi liquid state of the Falicov-Kimball model. We compute
observables relevant to cold atom systems such as the double occupation, the
specific heat and entropy and characterize their behavior in the different
phases
Weak coupling study of decoherence of a qubit in disordered magnetic environments
We study the decoherence of a qubit weakly coupled to frustrated spin baths.
We focus on spin-baths described by the classical Ising spin glass and the
quantum random transverse Ising model which are known to have complex
thermodynamic phase diagrams as a function of an external magnetic field and
temperature. Using a combination of numerical and analytical methods, we show
that for baths initally in thermal equilibrium, the resulting decoherence is
highly sensitive to the nature of the coupling to the environment and is
qualitatively different in different parts of the phase diagram. We find an
unexpected strong non-Markovian decay of the coherence when the random
transverse Ising model bath is prepared in an initial state characterized by a
finite temperature paramagnet. This is contrary to the usual case of
exponential decay (Markovian) expected for spin baths in finite temperature
paramagnetic phases, thereby illustrating the importance of the underlying
non-trivial dynamics of interacting quantum spinbaths.Comment: 12 pages, 18 figure
Phase diagram of the asymmetric Hubbard model and an entropic chromatographic method for cooling cold fermions in optical lattices
We study the phase diagram of the asymmetric Hubbard model (AHM), which is
characterized by different values of the hopping for the two spin projections
of a fermion or equivalently, two different orbitals. This model is expected to
provide a good description of a mass-imbalanced cold fermionic mixture in a 3D
optical lattice. We use the dynamical mean field theory to study various
physical properties of this system. In particular, we show how
orbital-selective physics, observed in multi-orbital strongly correlated
electron systems, can be realized in such a simple model. We find that the
density distribution is a good probe of this orbital selective crossover from a
Fermi liquid to a non-Fermi liquid state.
Below an ordering temperature , which is a function of both the
interaction and hopping asymmetry, the system exhibits staggered long range
orbital order. Apart from the special case of the symmetric limit, i.e.,
Hubbard model, where there is no hopping asymmetry, this orbital order is
accompanied by a true charge density wave order for all values of the hopping
asymmetry. We calculate the order parameters and various physical quantities
including the thermodynamics in both the ordered and disordered phases. We find
that the formation of the charge density wave is signaled by an abrupt increase
in the sublattice double occupancies. Finally, we propose a new method,
entropic chromatography, for cooling fermionic atoms in optical lattices, by
exploiting the properties of the AHM. To establish this cooling strategy on a
firmer basis, we also discuss the variations in temperature induced by the
adiabatic tuning of interactions and hopping parameters.Comment: 16 pages, 19 fig
Decomposing and re-composing lightweight compression schemes - and why it matters
We argue for a richer view of the space of lightweight compression schemes for columnar DBMSes: We demonstrate how even simple simple schemes used in DBMSes decompose into constituent schemes through a columnar perspective on their decompression. With our concrete examples, we touch briefly on what follows from these and other decompositions: Composition of alternative compression schemes as well as other practical and analytical implications
Mott transition in the Hubbard model away from particle-hole symmetry
We solve the Dynamical Mean Field Theory equations for the Hubbard model away
from the particle-hole symmetric case using the Density Matrix Renormalization
Group method. We focus our study on the region of strong interactions and
finite doping where two solutions coexist. We obtain precise predictions for
the boundaries of the coexistence region. In addition, we demonstrate the
capabilities of this precise method by obtaining the frequency dependent
optical conductivity spectra.Comment: 4 pages, 4 figures; updated versio
Landau Theory of the Finite Temperature Mott Transition
In the context of the dynamical mean-field theory of the Hubbard model, we
identify microscopically an order parameter for the finite temperature Mott
endpoint. We derive a Landau functional of the order parameter. We then use the
order parameter theory to elucidate the singular behavior of various physical
quantities which are experimentally accessible.Comment: 4 pages, 2 figure
Serializing the Parallelism in Parallel Communicating Pushdown Automata Systems
We consider parallel communicating pushdown automata systems (PCPA) and
define a property called known communication for it. We use this property to
prove that the power of a variant of PCPA, called returning centralized
parallel communicating pushdown automata (RCPCPA), is equivalent to that of
multi-head pushdown automata. The above result presents a new sub-class of
returning parallel communicating pushdown automata systems (RPCPA) called
simple-RPCPA and we show that it can be written as a finite intersection of
multi-head pushdown automata systems
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