Quantum device applications of mesoscopic superconductivity

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Doctoral thesis (article-based)
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Experimental condensed-matter physics
Degree programme
99, [68]
The work involves a study of physical phenomena that take place at very small length scales, below one micro-meter. At temperatures roughly below one degree Kelvin, quantum-mechanical effects may rule in electronic transport. Macroscopic quantum-coherent effects that occur in metallic superconducting microstructures, are particularly intriguing. Large-scale quantum information processing is widely believed to be attainable utilizing such physical systems. This work concentrates on answering the question of how the described quantum-mechanical systems may be used as sensitive measuring devices. Considerable attention is paid to energy-storing metallic microstructures whose electrical properties resemble those of the familiar inductor or capacitor. This research involves primarily experimental investigations conducted around temperatures of 0.1 Kelvin. Methods both at low and at radio frequencies have been used. The experimental findings have been modelled theoretically, and theoretical concepts for new physical phenomena have been introduced. An inductively measured radio-frequency Cooper-pair transistor, the L-SET, has been developed and experimentally verified in this work. Being highly sensitive, fast, and non-invasive, the L-SET appears to be the most promising method for measuring electric charge. Sensitivity in charge measurements of 20 millionths of the electron charge (micro-e) within one second, and an input bandwidth of 100 MHz, have been demonstrated. It has been shown theoretically that the ultimate measurement accuracy is about 0.1 micro-e within a second. A new phase detector based on the Cooper-pair transistor has been proposed. This system has also been shown to be potentially usable as a quantum bit. A new type of radio-frequency single-electron transistor built using a multi-walled carbon nanotube has been fabricated and operated. Technologies have been developed in order to make the physical nano- or microstructures. A method has been presented to fabricate non-superconducting tunnel junctions. Consequences of the inverse superconducting proximity effect on the studied superconducting structures were considered. Measurement procedures were investigated for a new low-noise nanoamplifier, the Bloch-oscillating transistor. Single superconducting tunnel junctions were tested as detectors of energy states of the environment, or of noise.
Supervising professor
Salomaa, Martti M.; Prof.
Thesis advisor
Hakonen, Pertti J.; Prof.
high-frequency techniques, single-electron transistor, quantum measurement
Other note
  • M. A. Sillanpää, T. T. Heikkilä, R. K. Lindell, and P. J. Hakonen. 2001. Inverse proximity effect in superconductors near ferromagnetic material. Europhysics Letters 56, pages 590-595. [article1.pdf] © 2001 EDP Sciences. By permission.
  • M. A. Sillanpää and P. J. Hakonen. 2002. Titanium single-electron transistor fabricated by electron-beam lithography. Physica E 15, pages 41-47. [article2.pdf] © 2002 Elsevier Science. By permission.
  • J. Delahaye, J. Hassel, R. Lindell, M. Sillanpää, M. Paalanen, H. Seppä, and P. Hakonen. 2002. Low-noise current amplifier based on mesoscopic Josephson junction. Science 299, pages 1045-1048.
  • R. Lindell, J. Penttilä, M. Sillanpää, and P. Hakonen. 2003. Quantum states of a mesoscopic SQUID measured using a small Josephson junction. Physical Review B 68, 052506. [article4.pdf] © 2003 American Physical Society. By permission.
  • L. Roschier, M. Sillanpää, T. Wang, M. Ahlskog, S. Iijima, and P. Hakonen. 2004. Carbon nanotube radio-frequency single-electron transistor. Journal of Low Temperature Physics 136, pages 465-480.
  • M. A. Sillanpää, L. Roschier, and P. J. Hakonen. 2004. Inductive single-electron transistor. Physical Review Letters 93, 066805. [article6.pdf] © 2004 American Physical Society. By permission.
  • M. A. Sillanpää, L. Roschier, and P. J. Hakonen. 2005. Dynamics of the inductive single-electron transistor. In: D. C. Glattli, M. Sanquer, and J. Trân Thanh Vân (editors), Quantum Information and Decoherence in Nanosystems. Proceedings of the Vth Rencontres de Moriond in Mesoscopic Physics, to appear.
  • M. A. Sillanpää, L. Roschier, and P. J. Hakonen. 2005. Direct measurements of tunable Josephson plasma resonance in the L-SET. In: P. Delsing, C. Granata, Y. Pashkin, B. Ruggiero, and P. Silvestrini (editors), Quantum Computation: solid state systems. Proceedings of the IV International Workshop on Macroscopic Quantum Coherence and Computing, to appear.
  • L. Roschier, M. A. Sillanpää, and P. Hakonen. 2005. Quantum capacitive phase detector. Physical Review B 71, 024530. [article9.pdf] © 2005 American Physical Society. By permission.
  • M. A. Sillanpää, L. Roschier, and P. J. Hakonen. 2005. Charge sensitivity of the inductive single-electron transistor. Helsinki University of Technology, Low Temperature Laboratory Publications, TKK-KYL-013, R2005017. Applied Physics Letters, submitted for publication.
  • R. K. Lindell, J. Delahaye, M. A. Sillanpää, T. T. Heikkilä, E. B. Sonin, and P. J. Hakonen. 2004. Observation of shot-noise-induced asymmetry in the Coulomb blockaded Josephson junction. Physical Review Letters 93, 197002. [article11.pdf] © 2004 American Physical Society. By permission.
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