Summary

Abstract

We started our journey through quantum networks with elementary spins such as the electron and the photon spin, both described by the SU(2) algebra. We then generalized to pseudospins realized by 2-level systems or restricted number states (for example of cavity photon modes) and to 3- or 4-level systems that implemented SU(3) or SU(4) algebras. Both static and dynamic properties have been investigated. In general, quantum objects inhabit a large (n² − 1)-dimensional space. Furthermore, if the system consists of N interacting nodes, many-node coherence (“entanglement”) has to be taken into account, in addition to single-node coherence. The theoretical description of coherence in the case of 2- and 3-node networks has been studied. The discussion of typical 2-node coherence apparently started with Aspect’s experiments on entangled photon states and the Kocher-Cummings experiment. Greenberger-Horne-Zeilinger states (GHZ states), i.e. special 3- and 4-node coherent states which are leading to new experimental schemes, and their interesting theoretical properties have been examined.