17 research outputs found
Diabatic quantum and classical annealing of the Sherrington-Kirkpatrick model
Quantum annealing is a contender to solve combinatorial optimization problems
based on quantum dynamics. While significant efforts have been undertaken to
investigate the quality of the solutions and the required runtimes, much less
attention has been paid to understanding the dynamics of quantum annealing and
the process leading to the solution during the sweep itself. In this
comprehensive study, we investigate various aspects of the quantum annealing
dynamics using different approaches. We perform quantum annealing, simulated
quantum annealing, and classical annealing on several hundred instances of the
Sherrington-Kirkpatrick model with intermediate system sizes up to 22 spins
using numerical simulations. We observe qualitative differences between the
quantum and classical methods, in particular at intermediate times, where a
peak in the fidelity, also known as diabatic bump, appears for hard instances.
Furthermore, we investigate the two-point correlation functions, which feature
differences at intermediate times as well. At short times, however, the methods
are similar again, which can be explained by relating the short-time expansion
of quantum annealing to a high-temperature expansion, thus allowing in
principle to find the classical solution already at short times, albeit at
prohibitive sampling cost.Comment: revised version: 22 pages, 11 figure
Hydrodynamic Chromatography Coupled with Single Particle-Inductively Coupled Plasma Mass Spectrometry for Investigating Nanoparticles Agglomerates
Studying
the environmental fate of engineered or natural colloids requires
efficient methods for measuring their size and quantifying them in
the environment. For example, an ideal method should maintain its
correctness, accuracy, reproducibility, and robustness when applied
to samples contained in complex matrixes and distinguish the target
particles from the natural colloidal background signals. Since it
is expected that a large portion of nanoparticles will form homo-
or heteroagglomerates when released into environmental media, it is
necessary to differentiate agglomerates from primary particles. At
present, most sizing techniques do not fulfill these requirements.
In this study, we used online coupling of two promising complementary
sizing techniques: hydrodynamic chromatography (HDC) and single-particle
ICPMS analysis to analyze gold nanoparticles agglomerated under controlled
conditions. We used the single-particle mode of the ICPMS detector
to detect single particles eluted from an HDC-column and determine
a mass and an effective diameter for each particle using a double
calibration approach. The average agglomerate relative density and
fractal dimension were calculated using these data and used to follow
the morphological evolution of agglomerates over time during the agglomeration
process. The results demonstrate the ability of HDC coupled to single-particle
analysis to identify and characterize nanoparticle homoagglomerates
and is a very promising technique for the analysis of colloids in
complex media