Triple exceptional points in a tunable superconducting circuit

Exceptional points (EPs) correspond to singularities in non-Hermitian Hamiltonians typically describing effective open quantum dynamics. Besides the mathematical interest that is inherent to EPs, their relevance for practical tasks such as energy transfer and quantum sensing has been recently acknowledged in superconducting circuits that behave as effective two-level systems. However, the production of higher order EPs in such technologies is still prone to difficulties owing to the increase of parameter space and necessity of precise control, which opens room for new circuit designs. In this context, we study the occurrence of EPs in a superconducting circuit consisting of three coupled resonators with tunable dissipation rates and resonance frequencies. We present the dynamics of this system and show the general conditions to obtain a triple exceptional point. Our results may provide a better understanding of energy transfer and guide near-term experiments with engineered environments. 

Funding acknowledgment: Academy of Finland Centre of Excellence program (project no. 336810) and European Research Council under Grant no. 681311 (QUESS).