Harvesting Multiqubit Entanglement from Ultrastrong Interactions in Circuit Quantum Electrodynamics.

F Armata,T Jaako,G Calajo,M S Kim,P Rabl

doi:10.1103/physrevlett.119.183602

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.

Highlights

Cavity QED is the study of quantum light-matter interactions with real or artificial two-level atoms coupled to a single radiation mode. In this context one is usually interested in strong interactions between excited atomic and electromagnetic states, while the trivial ground state, i.e., the vacuum state with no atomic or photonic excitations, plays no essential role
Compared to the vast literature on cavity QED systems in the weakly coupled regime, the opposite limit of extremely strong interactions is to a large extent still unexplored
In this Letter we consider a prototype circuit QED system consisting of multiple flux qubits coupled to a single mode of a microwave resonator

Summary

Introduction

Cavity QED is the study of quantum light-matter interactions with real or artificial two-level atoms coupled to a single radiation mode. We analyze a multiqubit circuit QED system in the regime where the qubit-photon coupling dominates over the system’s bare energy scales. We describe a time-dependent protocol for extracting these quantum correlations and converting them into well-defined multipartite entangled states of noninteracting qubits.

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Results

Conclusion