1,176 research outputs found
Collision of one-dimensional fermion clusters
We study cluster-cluster collisions in one-dimensional Fermi systems with
particular emphasis on the non-trivial quantum effects of the collision
dynamics. We adopt the Fermi-Hubbard model and the time-dependent density
matrix renormalization group method to simulate collision dynamics between two
fermion clusters of different spin states with contact interaction. It is
elucidated that the quantum effects become extremely strong with the
interaction strength, leading to the transmittance much more enhanced than
expected from semiclassical approximation. We propose a concise model based on
one-to-one collisions, which unveils the origin of the quantum effects and also
explains the overall properties of the simulation results clearly. Our concise
model can quite widely describe the one-dimensional collision dynamics with
contact interaction. Some potential applications, such as repeated collisions,
are addressed.Comment: 5 pages, 5 figure
Observation of Conduction Band Satellite of Ni Metal by 3p-3d Resonant Inverse Photoemission Study
Resonant inverse photoemission spectra of Ni metal have been obtained across
the Ni 3 absorption edge. The intensity of Ni 3 band just above Fermi
edge shows asymmetric Fano-like resonance. Satellite structures are found at
about 2.5 and 4.2 eV above Fermi edge, which show resonant enhancement at the
absorption edge. The satellite structures are due to a many-body configuration
interaction and confirms the existence of 3 configuration in the ground
state of Ni metal.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Density-matrix renormalization group study of pairing when electron-electron and electron-phonon interactions coexist: effect of the electronic band structure
Density-matrix renormalization group is used to study the pairing when both
of electron-electron and electron-phonon interactions are strong in the
Holstein-Hubbard model at half-filling in a region intermediate between the
adiabatic (Migdal's) and antiadiabatic limits. We have found: (i) the pairing
correlation obtained for a one-dimensional system is nearly degenerate with the
CDW correlation in a region where the phonon-induced attraction is comparable
with the electron-electron repulsion, but (ii) pairing becomes dominant when we
destroy the electron-hole symmetry in a trestle lattice. This provides an
instance in which pairing can arise, in a lattice-structure dependent manner,
from coexisting electron-electron and electron-phonon interactions.Comment: 4 pages, 3 figures; to appear in Phys. Rev. Let
Computation over galois fields using shiftregisters
This paper presents a technique for readily determining the shiftregister which multiplies by a given element of GF(2m)}, or which raises a given element of GF(2m)} to a given power. A matrix (called a connection matrix) is derived from a primitive polynomial and is corresponded to a particular shiftregister. The nth power of the matrix corresponds to the shiftregister which multiplies by Xn. Examples are presented to illustrate the application of the technique
Time-evolution of the Rule 150 cellular automaton activity from a Fibonacci iteration
The total activity of the single-seeded cellular rule 150 automaton does not
follow a one-step iteration like other elementary cellular automata, but can be
solved as a two-step vectorial, or string, iteration, which can be viewed as a
generalization of Fibonacci iteration generating the time series from a
sequence of vectors of increasing length. This allows to compute the total
activity time series more efficiently than by simulating the whole
spatio-temporal process, or even by using the closed expression.Comment: 4 pages (3 figs included
Onset of Random Matrix Behavior in Scrambling Systems
The fine grained energy spectrum of quantum chaotic systems is widely
believed to be described by random matrix statistics. A basic scale in such a
system is the energy range over which this behavior persists. We define the
corresponding time scale by the time at which the linearly growing ramp region
in the spectral form factor begins. We call this time . The
purpose of this paper is to study this scale in many-body quantum systems that
display strong chaos, sometimes called scrambling systems. We focus on randomly
coupled qubit systems, both local and -local (all-to-all interactions) and
the Sachdev--Ye--Kitaev (SYK) model. Using numerical results for Hamiltonian
systems and analytic estimates for random quantum circuits we find the
following results. For geometrically local systems with a conservation law we
find is determined by the diffusion time across the system,
order for a 1D chain of qubits. This is analogous to the behavior
found for local one-body chaotic systems. For a -local system with
conservation law the time is order but with a different prefactor and
a different mechanism than the scrambling time. In the absence of any
conservation laws, as in a generic random quantum circuit, we find , independent of connectivity.Comment: 61+20 pages, minor errors corrected, and significant edits in Section
Black Holes and Random Matrices
We argue that the late time behavior of horizon fluctuations in large anti-de
Sitter (AdS) black holes is governed by the random matrix dynamics
characteristic of quantum chaotic systems. Our main tool is the
Sachdev-Ye-Kitaev (SYK) model, which we use as a simple model of a black hole.
We use an analytically continued partition function as well
as correlation functions as diagnostics. Using numerical techniques we
establish random matrix behavior at late times. We determine the early time
behavior exactly in a double scaling limit, giving us a plausible estimate for
the crossover time to random matrix behavior. We use these ideas to formulate a
conjecture about general large AdS black holes, like those dual to 4D
super-Yang-Mills theory, giving a provisional estimate of the crossover time.
We make some preliminary comments about challenges to understanding the late
time dynamics from a bulk point of view.Comment: 73 pages, 15 figures, minor errors correcte
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