Feedback control of quantum entanglement in a two-spin system

Naoki Yamamoto, Koji Tsumura, Shinji Hara

Research output: Contribution to journalArticlepeer-review

71 Citations (Scopus)


A pair of spins is the most simple quantum system that can exhibit entanglement: a nonclassical property that plays an essential role in quantum information technologies. In this paper, feedback control problems of a symmetric two-spin system conditioned on a continuous measurement are investigated. In order to make some useful formulas in stochastic control theory directly applicable, we first derive a two-dimensional representation of the system. We then prove that a feedback controller stabilizes an entangled state of the two spins almost globally with probability one. Furthermore, it is demonstrated that some entangled states, which correspond to nonequilibrium points of the dynamics, are globally stabilized via feedback in the sense that the mean distance from a target can be reduced to an arbitrarily small value.

Original languageEnglish
Pages (from-to)981-992
Number of pages12
Issue number6
Publication statusPublished - 2007 Jun
Externally publishedYes


  • Feedback control
  • Quantum systems
  • Stochastic differential equation

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Electrical and Electronic Engineering


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