ABSTRACT
Yuki Kawaguchi Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Masahito Ueda Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Macroscopic Quantum Control Project, ERATO, JST, Bunkyo-ku, Tokyo 1138656, Japan
The defining character of a topological object is that it can move and deform freely in space and time, yet retains its identity, characterized by a set of discrete numbers called topological charges. This ability to deform without changing its fundamental character lends a particular importance to the notion of topological excitations that is independent of specific material properties. Such topological excitations are spontaneously generated under classical and quantum phase transitions. This chapter is devoted to an overview of topological excitations with an emphasis on spinor Bose-Einstein condensates (BECs).
