1,090 research outputs found
Comment on "Control landscapes are almost always trap free: a geometric assessment"
We analyze a recent claim that almost all closed, finite dimensional quantum
systems have trap-free (i.e., free from local optima) landscapes (B. Russell
et.al. J. Phys. A: Math. Theor. 50, 205302 (2017)). We point out several errors
in the proof which compromise the authors' conclusion.
Interested readers are highly encouraged to take a look at the "rebuttal"
(see Ref. [1]) of this comment published by the authors of the criticized work.
This "rebuttal" is a showcase of the way the erroneous and misleading
statements under discussion will be wrapped up and injected in their future
works, such as R. L. Kosut et.al, arXiv:1810.04362 [quant-ph] (2018).Comment: 6 pages, 1 figur
Supersonic dislocations observed in a plasma crystal
Experimental results on the dislocation dynamics in a two-dimensional plasma
crystal are presented. Edge dislocations were created in pairs in lattice
locations where the internal shear stress exceeded a threshold and then moved
apart in the glide plane at a speed higher than the sound speed of shear waves,
. The experimental system, a plasma crystal, allowed observation of this
process at an atomistic (kinetic) level. The early stage of this process is
identified as a stacking fault. At a later stage, supersonically moving
dislocations generated shear-wave Mach cones
Formation of singularities on the surface of a liquid metal in a strong electric field
The nonlinear dynamics of the free surface of an ideal conducting liquid in a
strong external electric field is studied. It is establish that the equations
of motion for such a liquid can be solved in the approximation in which the
surface deviates from a plane by small angles. This makes it possible to show
that on an initially smooth surface for almost any initial conditions points
with an infinite curvature corresponding to branch points of the root type can
form in a finite time.Comment: 14 page
Wigner phase space distribution as a wave function
We demonstrate that the Wigner function of a pure quantum state is a wave
function in a specially tuned Dirac bra-ket formalism and argue that the Wigner
function is in fact a probability amplitude for the quantum particle to be at a
certain point of the classical phase space. Additionally, we establish that in
the classical limit, the Wigner function transforms into a classical
Koopman-von Neumann wave function rather than into a classical probability
distribution. Since probability amplitude need not be positive, our findings
provide an alternative outlook on the Wigner function's negativity.Comment: 6 pages and 2 figure
Decay of metastable phases in a model for the catalytic oxidation of CO
We study by kinetic Monte Carlo simulations the dynamic behavior of a
Ziff-Gulari-Barshad model with CO desorption for the reaction CO + O
CO on a catalytic surface. Finite-size scaling analysis of the fluctuations
and the fourth-order order-parameter cumulant show that below a critical CO
desorption rate, the model exhibits a nonequilibrium first-order phase
transition between low and high CO coverage phases. We calculate several points
on the coexistence curve. We also measure the metastable lifetimes associated
with the transition from the low CO coverage phase to the high CO coverage
phase, and {\it vice versa}. Our results indicate that the transition process
follows a mechanism very similar to the decay of metastable phases associated
with {\it equilibrium} first-order phase transitions and can be described by
the classic Kolmogorov-Johnson-Mehl-Avrami theory of phase transformation by
nucleation and growth. In the present case, the desorption parameter plays the
role of temperature, and the distance to the coexistence curve plays the role
of an external field or supersaturation. We identify two distinct regimes,
depending on whether the system is far from or close to the coexistence curve,
in which the statistical properties and the system-size dependence of the
lifetimes are different, corresponding to multidroplet or single-droplet decay,
respectively. The crossover between the two regimes approaches the coexistence
curve logarithmically with system size, analogous to the behavior of the
crossover between multidroplet and single-droplet metastable decay near an
equilibrium first-order phase transition.Comment: 27 pages, 22 figures, accepted by Physical Review
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