Coherent transport in multi-terminal Aharonov-Bohm rings

Introduction Intriguing quantum phenomena emerge in the study of devices when size approaches characteristic length scales of the carriers such as phase- and mo mentum-relaxation lengths or Fermi wavelength. Today these regimes can be routinely realized in state-of-the-art condensed-matter physics laboratories taking adva ntage of the low disorder and long coherence lengths typical of semiconductor heterostructures and of the possibility to fabricate nanometer-sized features by e-beam processing. Devices realized with these novel nano-technologies open the way to the study of fundamental physical issues of mesoscopic systems and are exploited to develop new concepts for electronics. Among the various quantum phenomena observed when studying mesoscopic systems the Aharonov-Bohm (AB) effect is of particular interest for the implementation of coherent devices as it allows controlling the electro nic phase by means of external electric or magnetic fields. In particular, it was s hown that multiterminal devices based on the AB effects are ideal building blocks for the realization of quantum-network architectures based on the coherent evolution of the phase of electronic wavefunctions. Indeed, three-terminal Aharonov-B ohm rings configured with one input and two output channels can realize a Qubit encoded by the linear superposition of the two output states. The implementation of single-Qubit logic functions was proposed on tailored multi-terminal rings. This configuration attracted the interest of the theoretical condensed-matter community and was analyzed from several points of view by means of scattering-matrix approaches in the Landauer-Buttiker framework, free-electron-like node equations, and displaced Gaussian wavefunctions. In spite of the amount of theoretical research focused on this subject and its important technological implications a satisfactory comparison with experimental observations has not yet been carried out. The results presented in this thesis work belong to this context. ...