Enhanced Sensitivity near a Quantum Exceptional Point in a Parametrically Driven Superconducting Circuit

Non-Hermitian systems can display behavior absent in Hermitian ones, including exceptional points (EPs) where two or more eigenvectors coalesce. Such systems typically rely on loss and gain, which severely limit quantum coherence. In this talk, following a proposal by Wang and Clerk [1], we present a closed, four-mode quantum system that simulates the dynamics of a PT dimer—two coupled resonators, one with gain and the other with loss—without introducing dissipation or noise. The four modes are realized using harmonics of a superconducting coplanar waveguide resonator, and parametric couplings between the modes are demonstrated using a current-pumped SNAIL coupler. We then explore the device as a sensor for small variations in coupling. Measuring the signal-to-noise ratio, we observe an enhancement near the EP in this nearly quantum-noise-limited system.

[1] Yu-Xin Wang and A. A. Clerk, “Non-Hermitian dynamics without dissipation in quantum systems”, Phys. Rev. A 99, 063834 (2019)