Observation of the exceptional point in superconducting qubit with dissipation controlled by parametric modulation* *Project supported by the State Key Development Program for Basic Research of China (Grant Nos. 2017YFA0304300 and 2016YFA0300600), the Key-Area Research and Development Program of Guangdong Province, China (Grant No. 2020B0303030001), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000).

Abstract

Open physical systems described by the non-Hermitian Hamiltonian with parity-time-reversal (PT) symmetry show peculiar phenomena, such as the presence of an exceptional point (EP) at which the PT symmetry is broken and two resonant modes of the Hamiltonian become degenerate. Near the EP, the system could be more sensitive to external perturbations and this may lead to enhanced sensing. In this paper, we present experimental results on the observation of PT symmetry broken transition and the EP using a tunable superconducting qubit. The quantum system of investigation is formed by the two levels of the qubit and the energy loss of the system to the environment is controlled by a method of parametric modulation of the qubit frequency. This method is simple with no requirements for additional elements or qubit device modifications. We believe it can be easily implemented on multi-qubit devices that would be suitable for further exploration of non-Hermitian physics in more complex and diverse systems.