University of Oulu

Spectroscopy of artificial atoms and molecules

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Author: Tuorila, Jani1
Organizations: 1University of Oulu, Faculty of Science, Department of Physics, Division of Theoretical Physics
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 6.7 MB)
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Language: English
Published: Oulu : University of Oulu, 2010
Publish Date: 2011-03-15
Thesis type: Doctoral Dissertation
Defence Note: Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Auditorium L10, on June 4th, 2010, at 12 o’clock noon.
Reviewer: Professor Steven Girvin
Doctor Sorin Paraoanu
Opponent: Professor Steven Girvin
Kustos: Professor Erkki Thuneberg


Elementary experiments of atomic physics and quantum optics can be reproduced on a circuit board using elements built of superconducting materials. Such systems can show discrete energy levels similar to those of atoms. With respect to their natural cousins, the enhanced controllability of these ‘artificial atoms’ allows the testing of the laws of physics in a novel range of parameters. Also, the study of such systems is important for their proposed use as the quantum bits (qubits) of the foreseen quantum computer.

In this thesis, we have studied an artificial atom coupled with a harmonic oscillator formed by an LC-resonator. At the quantum limit, the interaction between the two can be shown to mimic that of ordinary matter and light. The properties of the system were studied by measuring the reflected signal in a capacitively coupled transmission line. In atomic physics, this has an analogy with the absorption spectrum of electromagnetic radiation. To simulate such measurements, we have derived the corresponding equations of motion using the quantum network theory and the semi-classical approximation. The calculated absorption spectrum shows a good agreement with the experimental data. By extracting the power consumption in different parts of the circuit, we have calculated the energy flow between the atom and the oscillator. It shows that, in a certain parameter range, the absorption spectrum obeys the Franck-Condon principle, and can be interpreted in terms of vibronic transitions of a diatomic molecule.

A coupling with a radiation field shifts the spectral lines of an atom. In our system, the interaction between the atom and the field is nonlinear, and we have shown that a strong monochromatic driving results in energy shifts unforeseen in natural or, even, other artificial atoms. We have used the Floquet method to calculate the quasienergies of the coupled system of atom and field. The oscillator was treated as a small perturbation probing the quasienergies, and the resulting absorption spectrum agrees with the reflection measurement.

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Series: Report series in physical sciences
ISSN: 1239-4327
ISSN-L: 1239-4327
ISBN: 978-951-42-6213-5
ISBN Print: 978-951-42-6212-8
Issue: 63
Copyright information: © University of Oulu, 2010. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.