Preface
Mesoscopic world represents a field of physics one step up from the atomic (microscopic) level. Quantum mechanical laws, well documented at the level of a single or a few atoms and electrons, are extended to sys-tems of size 1-100 nm containing 102 to 1010 electrons, still much smaller
than in the usual "macroscopic" objects, but behaving in a manner sim-ilar to single atom. Besides the pure theoretical interest, such systems are challenging in the process of achieving the ultimate microelectronic applications. The objective of this book is to bring together various di-rections in meso-large quantum systems, including such intriguing phe-nomena as quantization of magnetic flux (the Aharonov-Bohm effect) and quantization of electric charge (the Coulomb blockade and Coulomb oscillation effects); quantization of electrical resistance in mesoscopic conductors and, in general, aspects of quantum transport in mesoscopic, nanoscopic and atomic contacts formed between the metallic, semicon-ducting and superconsemicon-ducting electrodes; Josephson effect and Andreev reflection in small tunneling junctions as well as manifestations of quan-tum coherence in normal-conducting metals (the persistent currents).
We tried to put material presented at the NATO Advanced Study Institute on Quantum Mesoscopic Phenomena and Mesoscopic Devices in Microelectronics (Ankara/Antalya, June 13-25, 1999) related to these issues in a systematic way by collecting major topics into parts in the book.
In Part 1, atomic and ballistic contacts between metals are discussed as counterparts to more familiar tunneling contacts (tunneling junctions) which have been pioneers in the electronic applications. The recent ad-vances in nanofabrication technology made possible the preparation of direct metallic constrictions with dimensions down to atomic sizes. The flow of current in a constriction is a regular process with a reduced shot noise and therefore appealing for low-noise circuits, and quantized conductance in units of a fundamental quantity 2e2/h, twice the
funda-mental conductance quantum e2/h (a "klitzing") first appeared in the
physics of Quantum Hall Effect.
Part II considers phenomena associated with the so called Coulomb blockade as well as Coulomb oscillation in small metallic islands. This direction of mesoscopic physics promises the fastest applications in mi-croelectronics, and is already being used in the super-sensitive scientific instrumentation.
Part III addresses the fundamental issue of mesoscopic physics: which is the maximal spatial size, and the maximal temporal scale at which quantum coherence in a mesoscopic system is preserved? "Dephasing"
XlV Quantum Mesoscopic Phenomena
is a factor which limits the existence of quantum behavior in a system comprising many linear, as well as nonlinear electronic components, and therefore establishes a limit for the advanced applications of quantum phenomena like for example the quantum computation.
In Part IV, the Aharonov-Bohm effect and the related phenomena of "persistent" currents in various mesoscopic geometries are reviewed.
Part V is devoted to Josephson effect with a new angle of thought related to mesoscopic objects and to new artificially fabricated states of matter like Bose-Einstein condensates.
Part VI is devoted to mesoscopic superconductivity and pairing effect in ultrasmall superconducting grains. The trend in recent mesoscopic development directs to solid-state realization of the ultimate goal in the macroscopic quantum physics: the quantum computation, which is considered in Part VII (while some aspects of optoelectronic physics se-lected to Part VIII). The multi-degree of freedom (multi-qubit) quantum system develops, through the unitary transformation of its global wave function, a process similar to multi-bit computation. This "parallel pro-cessing" may dramatically increase the speed of computers as compared to standard classical Von Neumann computers. The papers mentioned in Part VIII illustrate the progress so far achieved in the fulfillment of this ultimate goal.
We thank the lecturers and the speakers of this NATO-ASI for de-livering their particular subjects with a special care for the global task: the understanding and developing of the quantum aspects of mesoscopic structures. Special thanks are addressed to the members of Interna-tional and Local Organizing Committees: Antonio Barone, Joseph Imry, Konstantin Likharev, Cemal Yalabik and Bilal Tanatar. Their valuable advises determined the scope of the Meeting and its final success. We thank Bilkent University which served as a host of the Meeting in its Ankara period, and Ador Tourizm and Travel Agency for the excellent organization of the second period of the Meeting in a stimulating atmo-sphere of small suburb of Antalya at the Mediterranean coast of Turkey.
It is our pleasure to acknowledge the generous grant by the Scientific Af-fairs Division of the North Atlantic Treaty Organization (NATO) which made our Meeting possible. We acknowledge the support by the Abdus Salam International Centre for Theoretical Physics (ICTP), as well as partial support by National Science Foundation (USA), the Centre Cul-turel et Linguistique (France), and Deutsche Forschungs Gemeinschaft (Germany) for the young scientists from the respective countries.
