We survey the most important results and some recent developments about the secure key exchange protocol where the security is based on the Second Law of Thermodynamics and the robustness of classical physical information. We conclude that a classical physical system offers a higher level of control and security during the communication. We also mention some recent attempts inspired by this communicator to create other systems where Alice and Bob do not form an organic single system and/or the Second Law is irrelevant. It seems philosophically that they cannot be unconditionally secure, however it is yet an open question how to crack them; how can they be best used for conditionally secure communications, and what are the practical implications.
ブラウン回路は,その動作中に,ノイズとゆらぎをメカニズムとして積極的に使用する回路である.従来の回路では,ノイズは,抑制することによって制御してきたが,この方法は,電子回路の集積密度の進展につれて適切ではなくなりつつある.規模がナノスケールの回路では,ノイズのレベルが高く,これとは別の方法が必要になると想定される.この論文は,われわれ自身が実行した取り組みを中心に,この枠組みにおける研究活動について簡潔に考察するものである.