**Abstract**
Different from other physical theories, Quantum Mechanics (QM) is not based on physical principles, i.e., physical statements testable by experiments, but on abstract mathematics such as operators on Hilbert spaces. This is one of the cause to prevent the intuitive understanding of QM, and has long been considered as one of the most important problems of the foundations of QM.

In this seminar, I review the problem based on General Probabilistic Theories (GPTs), which give the most general framework of probabilistic models in terms of operational viewpoints such as preparation of states and measurements.

Finally, I introduce our recent result on the derivation of qubit from some simple physical principles.

[1] 数理科学2009年12月号 特集「《原理》の探求」-- 深遠なる物理法則の源に迫る -- 『量子力学の原理を求めて』 木村元

[2] G. Kimura, K. Nuida, H. Imai (in preparation).