166th RQC Seminar

• 講演者

  中川 大也 助教
  ( 東京大学 理学系研究科　物理学専攻　物理学科 )

• 日程

  2024年10月23日（水） 4:00-5:00 p.m. （16:00-17:00）

• 開催場所

  ハイブリッド（ZOOM・ Wako Main Research 3F 345-347 Seminar Room/ 研究本館3階 セミナー室(345-347) C01）

• 講演タイトル

  Topology of discrete quantum feedback control

• お問合せ

  rqc_info[at]ml.riken.jp

講演概要
Symmetry and topology are guiding principles for the classification of quantum phases of matter. For instance, unique gapped ground states of quantum many-body systems are classified into symmetry-protected topological phases, where different phases cannot be continuously connected with each other while preserving symmetry and an energy gap [1]. One can also utilize symmetry and topology to classify nonequilibrium dynamics. Examples include Floquet topological phases with topological unitary operators [2] and non-Hermitian topological phases in open systems [3]. In this seminar, we develop a framework of a topological classification of quantum channels that describe discrete quantum feedback control [4]. We construct a topological Maxwell's demon that achieves robust feedback-assisted chiral transport due to its topological nature. Furthermore, we provide a symmetry classification of quantum feedback control and show that only ten symmetry classes out of the 38-fold Bernard-LeClair classes are consistent with projective measurement. Building on the symmetry classification, we construct symmetry-protected topological feedback control which exhibits helical spin transport due to nontrivial point-gap topology.

[1] X. Chen, Z. C. Gu, Z. X. Liu, and X. G. Wen, Phys. Rev. B 87, 155114 (2013).
[2] T. Kitagawa, E. Berg, M. Rudner, and E. Demler, Phys. Rev. B 82, 235114 (2010).
[3] Z. Gong, Y. Ashida, K. Kawabata, K. Takasan, S. Higashikawa, and M. Ueda, Phys. Rev. X 8, 031079 (2018).
[4] M. Nakagawa and M. Ueda, arXiv:2403.08406.