50,594 research outputs found
Spatial noise correlations of a chain of ultracold fermions - A numerical study
We present a numerical study of noise correlations, i.e., density-density
correlations in momentum space, in the extended fermionic Hubbard model in one
dimension. In experiments with ultracold atoms, these noise correlations can be
extracted from time-of-flight images of the expanding cloud. Using the
density-matrix renormalization group method to investigate the Hubbard model at
various fillings and interactions, we confirm that the shot noise contains full
information on the correlations present in the system. We point out the
importance of the sum rules fulfilled by the noise correlations and show that
they yield nonsingular structures beyond the predictions of bosonization
approaches. Noise correlations can thus serve as a universal probe of order and
can be used to characterize the many-body states of cold atoms in optical
lattices.Comment: 12 pages, 7 figure
Decay Rates and Survival Probabilities in Open Quantum Systems
We provide the first statistical analysis of the decay rates of strongly
driven 3D atomic Rydberg states. The distribution of the rates exhibits
universal features due to Anderson localization, while universality of the time
dependent decay requires particular initial conditions.Comment: 4 pages, 3 figures, ref. on subjec
Global analysis of parallel analog networks with retarded feedback
We analyze the retrieval dynamics of analog ‘‘neural’’ networks with clocked sigmoid elements and multiple signal delays. Proving a conjecture by Marcus and Westervelt, we show that for delay-independent symmetric coupling strengths, the only attractors are fixed points and periodic limit cycles. The same result applies to a larger class of asymmetric networks that may be utilized to store temporal associations with a cyclic structure. We discuss implications for various learning schemes in the space-time domain
Matrix product state approach for a two-lead, multi-level Anderson impurity model
We exploit the common mathematical structure of the numerical renormalization
group and the density matrix renormalization group, namely, matrix product
states, to implement an efficient numerical treatment of a two-lead,
multi-level Anderson impurity model. By adopting a star-like geometry, where
each species (spin and lead) of conduction electrons is described by its own
Wilson chain, instead of using a single Wilson chain for all species together,
we achieve a very significant reduction in the numerical resources required to
obtain reliable results. We illustrate the power of this approach by
calculating ground state properties of a four-level quantum dot coupled to two
leads. The success of this proof-of-principle calculation suggests that the
star geometry constitutes a promising strategy for future calculations the
ground state properties of multi-band, multi-level quantum impurity models.
Moreover, we show that it is possible to find an "optimal" chain basis,
obtained via a unitary transformation (acting only on the index distinguishing
different Wilson chains), in which degrees of freedom on different Wilson
chains become effectively decoupled from each other further out on the Wilson
chains. This basis turns out to also diagonalize the model's chain-to-chain
scattering matrix. We demonstrate this for a spinless two-lead model,
presenting DMRG-results for the mutual information between two sites located
far apart on different Wilson chains, and NRG results with respect to the
scattering matrix.Comment: extended version, 11 pages, 12 figure
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