RQC Seminar

70th RQC Seminar

• Speaker

  Prof. Adam Miranowicz
  ( Faculty of Physics
  Adam Mickiewicz University, Poland )

• Date

  16:00-17:00, August 4, 2023 (Friday)

• Venue

  Hybrid(ZOOM・ Wako Main Research 3F 345-347 Seminar Room(C01))

• Title

  Quantum exceptional points and related topics

• Inquiries

  rqc_info[at]ml.riken.jp

Abstract
When a quantum system is isolated from its environment, it is described by a Hermitian Hamiltonian. Its eigenvalues characterize the resonances frequency, while its eigenvectors describe the form of those resonances. If, however, the system interacts with its environment, some particles will leak, while others will enter.
For semiclassical systems, this loss and gain can be captured by a non-Hermitian Hamiltonian, whose eigenvalues represent both the resonance frequencies and lifetime. The presence of the environment can cause two different resonances to become the same, forcing the frequency and the lifetime to match. In this case, we speak of EPs, which are considered as the basis for enhanced sensing measures and are relevant to describe dynamical phase transitions and characterize topological phases of matter. Many exotic phenomena, such as parity-time symmetry breaking and unidirectional propagation, have been observed in the proximity of EPs. The vast majority of the studies on EPs, however, have focused on semiclassical models. To properly describe open quantum systems, quantum jumps, representing the instantaneous switching between the energy levels of the system, must be included. Using Liouvillian quantum jumps, we defined quantum EPs, and showed how, and if, they could correspond to semiclassical EPs. Recent experiments and numerous theoretical studies of various groups confirm the usefulness of quantum EPs proposed by us. Coauthors: Fabrizio Minganti, Ievgen I. Arkhipov, Chia-Yi Ju, Guang-Yin Chen, Jan Perina, and Franco Nori