Yogesh Joglekar

Department of Physics
Indiana University Purdue University Indianapolis (IUPUI)
U.S.A.

Quantum state tomography and PT breaking transitions in non-Hermitian open systems

Open systems with gain and loss, described by non-Hermitian Hamiltonians, have been a subject of intense research. In classical systems, the effect of their exceptional-point (EP) degeneracies has been observed through remarkable phenomena such as the parity-time symmetry breaking transition. However, the consequences of an EP for quantum evolution and decoherence are unexplored. Here, we will show how evolution under a non-Hermitian Hamiltonian is extracted from the traditional Lindblad dynamics. We will use post-selection on a three-level superconducting transmon circuit with tunable Rabi drive, dissipation, and detuning to carry out quantum state tomography of a single dissipative qubit in the vicinity of its EP. Quantum state tomography reveals the PT symmetry breaking transition at zero detuning, decoherence enhancement at finite detuning, and a quantum signature of the EP in the qubit relaxation state [1]. We will present a generalization to time-periodic (Floquet) non-Hermitian Hamiltonians, that is implemented in ultra-cold fermions in a trap. This analysis reveals PT transitions at vanishingly small gain-loss strengths and analogs of multi-photon Rabi effect [2]. Our observations demonstrate rich phenomena associated with non-Hermitian physics in the fully quantum regime and open routes to explore and harness exceptional point degeneracies for enhanced sensing and quantum information processing.

[1] Collaboration with Kater Murch’s group. arXiv:1901.07968 (to appear in Nature Physics).
[2] Collaboration with Le Luo’s group. Nature Communications 10, 855 (2019).