Preface A student's first encounter with quantum mechanics could be a trau Instead of the solid ith respect totim with its evitable she h S p (and tha s as a rule ons behave like a sort o arre notion- The she(he)will realize that,after all,things are not that bad:the fiunda ples.o mental equation of the new mechanics-the Schrodinger equation-is a with tiny hales The magn well-defined,perfectly respectable linear differential equation in t,and when left alone,the microscopic system evolves in a rigorously deter- ministic fashion.Not only that,but due to the quantization of finite of Dr. Akira Ton ra,Hitachi Ad motions,and intimately related to this,to the existence of a new funda- mental constant of Nature,the Planck constant,h,quantum mechanics provides a much sharper (and sometimes.far simpler)explanation of the properties of atoms than does classical mechanics.For instance,all atoms of the same kind,in their norma state,have rigorously identical properties.This fact is fundamenta,for instanc, tures and in the working of the macros world (solids.crystals biological phe na ete)Th age of the new mechan s ove the class 1 one is,of c ot lim ited to nomena in our dlectricaleol the la optics relate contem m mecha cs fo ater on or his study. the stu nt might分 tha physi cists today ar ating the validity of the standard model predictions sometimes to the eleventh digit,for instance the anomalous magnetic moment of the muon (a kind of heavy electron).Of course,here we are comparing a particular model of Nature with experiments:how ever.the standard model of fundamental interactions-quantum chro modynamics for strong interactions and the Glashow-Weinberg-Salam theory of electroweak interactions-are all based on relativistic quantum mechanics.In atomic physics,the agreement between theory and ex periment can be equally go ood and sometimes even more impressive.All this.finally will convince her (him)that we are indeed dealing with on of the most precise and perhans most elegant theories wn in On e day she or he might becom ra teacher,and may tart giving a course on quantum me Perhaps,after many years