The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Quantum Fluctuations and Transport in Mesoscopic Physics

Teemu Ojanen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 30th of November, 2007, at 12 o'clock noon.

Overview in PDF format (ISBN 978-951-22-9053-6)   [512 KB]
Dissertation is also available in print (ISBN 978-951-22-9052-9)


Mesoscopic physics and nanoelectronics concentrate on systems with dimensions somewhere between atomic and everyday macroscopic scale. Modern technology enables construction of submicron nanostructures where modeling based on classical physics has proven inadequate. It is possible to design electric circuits where dynamics of single electrons and photons are controlled using state-of-the-art experimental methods. For quantitative understanding of these systems it is necessary to resort to a quantum-mechanical description. Quantum phenomena, such as tunneling and a wave-like interference of particles, are essential ingredients of physics in mesoscopic systems. Field of mesoscopic physics contains a rich variety of topics ranging from fundamental condensed matter physics to quantum information processing and possible future technological applications.

This thesis presents theoretical studies of mesoscopic quantum phenomena in nanostructures and small electronic devices. We have focused on effects of environment fluctuations and investigated connections between fluctuations and transport phenomena. Decoherence in quantum bits (qubits) and quantum state engineering in superconducting circuits are also studied. The theoretical analysis in each case requires an open-system treatment.

Effects of current fluctuations on quantum probe systems have been studied in detail. We have calculated transitions induced by current noise and discussed how these could be used for characterization of fluctuations. We have also shown that electric fluctuations play a key role in radiation and photon heat transport in nanostructures. Motivated by recent advances in mesoscopic electron-photon systems, we have studied a response of a coupled resonator-qubit system, squeezing of quantum fluctuations in small superconducting circuits and investigated decoherence in Josephson flux qubits.

This thesis consists of an overview and of the following 7 publications:

  1. O.-P. Saira, V. Bergholm, T. Ojanen, and M. Möttönen, Equivalent qubit dynamics under classical and quantum noise, Physical Review A 75, 012308 (2007). © 2007 American Physical Society. By permission.
  2. Teemu Ojanen and Tero T. Heikkilä, Quantum transitions induced by the third cumulant of current fluctuations, Physical Review B 73, 020501(R) (2006). © 2006 American Physical Society. By permission.
  3. Tero T. Heikkilä and Teemu Ojanen, Quantum detectors for the third cumulant of current fluctuations, Physical Review B 75, 035335 (2007). © 2007 American Physical Society. By permission.
  4. Teemu Ojanen and Tero T. Heikkilä, State-dependent impedance of a strongly coupled oscillator-qubit system, Physical Review B 72, 054502 (2005). © 2005 American Physical Society. By permission.
  5. T. Ojanen, A. O. Niskanen, Y. Nakamura, and A. A. Abdumalikov Jr., Global relaxation of superconducting qubits, Physical Review B 76, 100505(R) (2007). © 2007 American Physical Society. By permission.
  6. Teemu Ojanen and Janne Salo, Possible scheme for on-chip element for squeezed microwave generation, Physical Review B 75, 184508 (2007). © 2007 American Physical Society. By permission.
  7. Teemu Ojanen and Tero T. Heikkilä, Photon heat transport in low-dimensional nanostructures, Physical Review B 76, 073414 (2007). © 2007 American Physical Society. By permission.

Keywords: mesoscopic quantum phenomena, decoherence and noise, quantum transport

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© 2007 Helsinki University of Technology

Last update 2011-05-26