621 research outputs found
Quantum Nonadiabatic Cloning of Entangled Coherent States
We propose a systematic approach to the basis set extension for nonadiabatic
dynamics of entangled combination of nuclear coherent states (CSs) evolving
according to the time-dependent variational principle (TDVP). TDVP provides a
rigorous framework for fully quantum nonadiabatic dynamics of closed systems,
however, quality of results strongly depends on available basis functions.
Starting with a single nuclear CS replicated vertically on all electronic
states, our approach clones this function when replicas of the CS on different
electronic states experience increasingly different forces. Created clones move
away from each other (decohere) extending the basis set. To determine a moment
for cloning we introduce generalized forces based on derivatives that maximally
contribute to a variation of the total quantum action and thus account for
entanglement of all basis functions.Comment: 2 fig
Illustrating Electric Conductivity Using the Particle-in-a-Box Model: Quantum Superposition is the Key
Most of the textbooks explaining electric conductivity in the context of
quantum mechanics provide either incomplete or semi-classical explanations that
are not connected with the elementary concepts of quantum mechanics. We
illustrate the conduction phenomena using the simplest model system in quantum
dynamics, a particle in a box (PIB). To induce the particle dynamics, a linear
potential tilting the bottom of the box is introduced, which is equivalent to
imposing a constant electric field for a charged particle. Although the PIB
model represents a closed system that cannot have a flow of electrons through
the system, we consider the oscillatory dynamics of the particle probability
density as the analogue of the electric current. Relating the amplitude and
other parameters of the particle oscillatory dynamics with the gap between the
ground and excited states of the PIB model allows us to demonstrate one of the
most basic dependencies of electric conductivity on the valence-conduction band
gap of the material
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