81,490 research outputs found
Waveform simulator synthesizes complex functions
Multichannel apparatus produces or simulates a complex curve which can be viewed on an oscilloscope display surface and can be adjusted to match an original complex experimentally produced curve
Constraints on Hidden Photon Models from Electron g-2 and Hydrogen Spectroscopy
The hidden photon model is one of the simplest models which can explain the
anomaly of the muon anomalous magnetic moment (g-2). The experimental
constraints are studied in detail, which come from the electron g-2 and the
hydrogen transition frequencies. The input parameters are set carefully in
order to take dark photon contributions into account and to prevent the
analysis from being self-inconsistent. It is shown that the new analysis
provides a constraint severer by more than one order of magnitude than the
previous result.Comment: 18 pages, 2 figures, 1 table. v2: minor correction
Some extensions of the Kuhn-Tucker results in concave programming
Some extensions of Kuhn-Tucker results in concave programmin
Luttinger liquid physics from infinite-system DMRG
We study one-dimensional spinless fermions at zero and finite temperature T
using the density matrix renormalization group. We consider nearest as well as
next-nearest neighbor interactions; the latter render the system inaccessible
by a Bethe ansatz treatment. Using an infinite-system alogrithm we demonstrate
the emergence of Luttinger liquid physics at low energies for a variety of
static correlation functions as well as for thermodynamic properties. The
characteristic power law suppression of the momentum distribution n(k) function
at T=0 can be directly observed over several orders of magnitude. At finite
temperature, we show that n(k) obeys a scaling relation. The Luttinger liquid
parameter and the renormalized Fermi velocity can be extracted from the density
response function, the specific heat, and/or the susceptibility without the
need to carry out any finite-size analysis. We illustrate that the energy scale
below which Luttinger liquid power laws manifest vanishes as the half-filled
system is driven into a gapped phase by large interactions
Approaching Many-Body Localization from Disordered Luttinger Liquids via the Functional Renormalization Group
We study the interplay of interactions and disorder in a one-dimensional
fermion lattice coupled adiabatically to infinite reservoirs. We employ both
the functional renormalization group (FRG) as well as matrix product state
techniques, which serve as an accurate benchmark for small systems. Using the
FRG, we compute the length- and temperature-dependence of the conductance
averaged over samples for lattices as large as sites. We
identify regimes in which non-ohmic power law behavior can be observed and
demonstrate that the corresponding exponents can be understood by adapting
earlier predictions obtained perturbatively for disordered Luttinger liquids.
In presence of both disorder and isolated impurities, the conductance has a
universal single-parameter scaling form. This lays the groundwork for an
application of the functional renormalization group to the realm of many-body
localization
Waveform simulator Patent
Sign wave generation simulator for variable amplitude, frequency, damping, and phase pulses for oscilloscope displa
Reducing the numerical effort of finite-temperature density matrix renormalization group transport calculations
Finite-temperature transport properties of one-dimensional systems can be
studied using the time dependent density matrix renormalization group via the
introduction of auxiliary degrees of freedom which purify the thermal
statistical operator. We demonstrate how the numerical effort of such
calculations is reduced when the physical time evolution is augmented by an
additional time evolution within the auxiliary Hilbert space. Specifically, we
explore a variety of integrable and non-integrable, gapless and gapped models
at temperatures ranging from T=infty down to T/bandwidth=0.05 and study both
(i) linear response where (heat and charge) transport coefficients are
determined by the current-current correlation function and (ii) non-equilibrium
driven by arbitrary large temperature gradients. The modified DMRG algorithm
removes an 'artificial' build-up of entanglement between the auxiliary and
physical degrees of freedom. Thus, longer time scales can be reached
Finite temperature dynamical DMRG and the Drude weight of spin-1/2 chains
We propose an easily implemented approach to study time-dependent correlation
functions of one dimensional systems at finite temperature T using the density
matrix renormalization group. The entanglement growth inherent to any
time-dependent calculation is significantly reduced if the auxiliary degrees of
freedom which purify the statistical operator are time evolved with the
physical Hamiltonian but reversed time. We exploit this to investigate the long
time behavior of current correlation functions of the XXZ spin-1/2 Heisenberg
chain. This allows a direct extraction of the Drude weight D at intermediate to
large T. We find that D is nonzero -- and thus transport is dissipationless --
everywhere in the gapless phase. At low temperatures we establish an upper
bound to D by comparing with bosonization
- …