RQC Seminar

145th RQC Seminar

• Speaker

  Prof. Karol Bartkiewicz
  ( Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University in Poznań, Poland )

• Date

  16:00-17:00 (4:00-5:00 p.m.), August 21, 2024 (Wednesday)

• Venue

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

• Title

  Experimental Liouvillian exceptional points for a quantum system without Hamiltonian singularities

• Inquiries

  rqc_info[at]ml.riken.jp

Abstract
Hamiltonian exceptional points (HEPs) are spectral degeneracies of non-Hermitian Hamiltonians describing classical and semiclassical open systems with losses and/or gain. However, this definition overlooks the occurrence of quantum jumps in the evolution of open quantum systems. These quantum effects are properly accounted for by considering quantum Liouvillians and their exceptional points (LEPs). Specifically, a LEP corresponds to the coalescence of two or more eigenvalues and the corresponding eigenmatrices of a given Liouvillian at critical values of external parameters [Minganti et al., Phys. Rev. A 100, 062131 (2019)]. Here, we explicitly describe how standard quantum process tomography, which reveals the dynamics of a quantum system, can be readily applied to detect and characterize quantum LEPs of quantum non-Hermitian systems. We conducted experiments on an IBM quantum processor to implement a prototype model simulating the decay of a single qubit
through competing channels, resulting in LEPs but not HEPs. Subsequently, we performed tomographic reconstruction of the corresponding experimental Liouvillian and its LEPs using both single- and two-qubit operations. This example underscores the efficacy of process tomography in tuning and observing LEPs even in the absence of HEPs.