# Optimized heat transfer at exceptional points in quantum circuits

## TL;DR

This paper demonstrates the experimental realization of an exceptional point in superconducting microwave circuits, enabling optimized heat transfer and tunable dissipation, with implications for quantum computing and PT-symmetric systems.

## Contribution

It introduces the first experimental realization of an exceptional point in superconducting circuits, showing tunable heat flow and dissipation control at the quantum level.

## Key findings

- Observation of a crossover from underdamped to overdamped coupling at the EP
- Demonstration of in situ tunable dissipation using photon-assisted tunneling
- Potential applications in qubit initialization and PT-symmetric system studies

## Abstract

Superconducting quantum circuits are potential candidates to realize a large-scale quantum computer. The envisioned large density of integrated components, however, requires a proper thermal management and control of dissipation. To this end, it is advantageous to utilize tunable dissipation channels and to exploit the optimized heat flow at exceptional points (EPs). Here, we experimentally realize an EP in a superconducting microwave circuit consisting of two resonators. The EP is a singularity point of the Hamiltonian, and corresponds to the most efficient heat transfer between the resonators without oscillation of energy. We observe a crossover from underdamped to overdamped coupling via the EP by utilizing photon-assisted tunneling as an \emph{in situ} tunable dissipative element in one of the resonators. The methods studied here can be applied to different circuits to obtain fast dissipation, for example, for initializing qubits to their ground states. In addition, these results pave the way towards thorough investigation of parity--time ($\mathcal{PT}$) symmetric systems and the spontaneous symmetry breaking in superconducting microwave circuits operating at the level of single energy quanta.