arXiv subjects

Natascha Riahi

Publications and source records attributed to Natascha Riahi.

5 recordsLinked to original sources

arXiv2021

How to use Unimodular Quantum Cosmology for the Prediction of a late-time Classical Universe?

Unimodular quantum cosmology admits wavepacket solutions that evolve according to a kind of Schrödinger equation. Though this theory is equivalent to general relativity on the classical level, its canonical structure is different and the problem of time does not occur. We present an Ehrenfest theorem for the long term evolution of the expectation value of the scale factor for a spatially flat Friedmann universe with a scalar field. We find that the classical and the quantum behaviour in the asymptotic future coincide for the special case of a massless scalar field. We examine the general behaviour of uncertainties in order to single out models that can lead to a classical universe.

gr-qc↗

arXiv2019

Analysis of wavepacket tunneling with the method of Laplace transformation

We use the method of Laplace transformation to determine the dynamics of a wave packet that passes a barrier by tunneling. We investigate the transmitted wave packet and find that it can be resolved into a sequence of subsequent wave packages. This result sheds new light on the Hartmann effect for the tunneling time and gives a possible explanation for an experimental result obtained by Spielmann et. al.

quant-ph↗

arXiv2018

Wavepacket evolution in unimodular quantum cosmology

The unimodular theory of gravity admits a canonical quantization of minisuperspace models without the problem of time. We derive instead a kind of Schrödinger equation. We have found unitarily evolving wave packet solutions for the special case of a massless scalar field and a spatially flat Friedmann universe. We show that the longterm behaviour of the expectation values of the canonical quantities corresponds to the evolution of the classical variables. The solutions provided in an explicit example can be continued beyond the singularity at t=0, passing a finite minimal extension of the universe.

gr-qc↗

arXiv2016

Solving the time-dependent Schrödinger equation via Laplace transform

We show how the Laplace transform can be used to give a solution of the time-dependent Schrödinger equation for an arbitrary initial wave packet if the solution of the stationary equation is known. The solution is obtained without summing up eigenstates nor do we need the path integral. We solve the initial value problem for three characteristic piecewise constant potentials. The results give an intuitive picture of the wave packet dynamics, reproducing explicitly all possible reflection and transmission processes. We investigate classical and quantum properties of the evolution and determine the reflection and transmission probabilities.

quant-ph↗

arXiv2011

The evolution of quantal uncertainties in at most quadratic potentials

We investigate the time evolution of momentum and position uncertainties for wave packets of arbitrary shape in at most quadratic potentials. We consider all possible cases of potentials and initial conditions. Doing so we see that the mixed uncertainty and for Gaussian wave packets moreover the chirp are convenient and important tools to identify the characteristic features of uncertainty dynamics. Special attention is given to the spreading and narrowing of wave packets.

quant-ph↗