Harvesting Multiqubit Entanglement from Ultrastrong Interactions in Circuit Quantum Electrodynamics

Understand

We analyze a multiqubit circuit QED system in the regime where the qubit-photon coupling dominates over the system's bare energy scales.

• Under such conditions a manifold of low-energy states with a high degree of entanglement emerges.
• Here we describe a time-dependent protocol for extracting these quantum correlations and converting them into well-defined multipartite entangled states of noninteracting qubits.
• Based on a combination of various ultrastrong-coupling effects, the protocol can be operated in a fast and robust manner, while still being consistent with experimental constraints on switching times and typical energy scales encountered in superconducting circuits.