Harvesting Multiqubit Entanglement from Ultrastrong Interactions in Circuit Quantum Electrodynamics

TL;DR

This paper presents a protocol to extract and utilize multiqubit entanglement from ultrastrong coupling regimes in circuit QED, enabling access to otherwise inaccessible quantum correlations for quantum information applications.

Contribution

It introduces a time-dependent method to convert ultrastrong-coupling-induced entanglement into multipartite qubit states, compatible with experimental superconducting circuit constraints.

Findings

Protocol successfully extracts multipartite entanglement.

Operates robustly within experimental switching times.

Reveals hidden quantum correlations in ultrastrong coupling regimes.

Abstract

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. Therefore, our scheme can serve as a probe for otherwise inaccessible correlations in strongly coupled circuit QED systems. It also shows how such correlations can potentially be exploited as a resource for entanglement-based applications.