3,777 research outputs found
Adiabatic evolution on a spatial-photonic Ising machine
Combinatorial optimization problems are crucial for widespread applications
but remain difficult to solve on a large scale with conventional hardware.
Novel optical platforms, known as coherent or photonic Ising machines, are
attracting considerable attention as accelerators on optimization tasks
formulable as Ising models. Annealing is a well-known technique based on
adiabatic evolution for finding optimal solutions in classical and quantum
systems made by atoms, electrons, or photons. Although various Ising machines
employ annealing in some form, adiabatic computing on optical settings has been
only partially investigated. Here, we realize the adiabatic evolution of
frustrated Ising models with 100 spins programmed by spatial light modulation.
We use holographic and optical control to change the spin couplings
adiabatically, and exploit experimental noise to explore the energy landscape.
Annealing enhances the convergence to the Ising ground state and allows to find
the problem solution with probability close to unity. Our results demonstrate a
photonic scheme for combinatorial optimization in analogy with adiabatic
quantum algorithms and enforced by optical vector-matrix multiplications and
scalable photonic technology.Comment: 9 pages, 4 figure
A Quantum Monte Carlo Approach to the Adiabatic Connection Method
We present a new method for realizing the adiabatic connection approach in
density functional theory, which is based on combining accurate variational
quantum Monte Carlo calculations with a constrained optimization of the ground
state many-body wavefunction for different values of the Coulomb coupling
constant. We use the method to study an electron gas in the presence of a
cosine-wave potential. For this system we present results for the
exchange-correlation hole and exchange-correlation energy density, and compare
our findings with those from the local density approximation and generalized
gradient approximation.Comment: to be published in Advances in Quantum Chemistr
Excited states with selected CI-QMC: chemically accurate excitation energies and geometries
We employ quantum Monte Carlo to obtain chemically accurate vertical and
adiabatic excitation energies, and equilibrium excited-state structures for the
small, yet challenging, formaldehyde and thioformaldehyde molecules. A key
ingredient is a robust protocol to obtain balanced ground- and excited-state
Jastrow-Slater wave functions at a given geometry, and to maintain such a
balanced description as we relax the structure in the excited state. We use
determinantal components generated via a selected configuration interaction
scheme which targets the same second-order perturbation energy correction for
all states of interest at different geometries, and we fully optimize all
variational parameters in the resultant Jastrow-Slater wave functions.
Importantly, the excitation energies as well as the structural parameters in
the ground and excited states are converged with very compact wave functions
comprising few thousand determinants in a minimally augmented double-
basis set. These results are obtained already at the variational Monte Carlo
level, the more accurate diffusion Monte Carlo method yielding only a small
improvement in the adiabatic excitation energies. We find that matching
Jastrow-Slater wave functions with similar variances can yield excitations
compatible with our best estimates; however, the variance-matching procedure
requires somewhat larger determinantal expansions to achieve the same accuracy,
and it is less straightforward to adapt during structural optimization in the
excited state.Comment: 11 pages, 4 figure
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