Dynamics of entanglement via propagating microwave photons

TL;DR

This paper proposes a circuit QED experiment to generate and analyze entanglement between superconducting qubits coupled via propagating microwave photons, exploring regimes from weak to ultrastrong coupling with a full quantum field theory approach.

Contribution

It introduces a novel open transmission line setup for entanglement generation and provides a comprehensive theoretical analysis beyond the rotating-wave approximation.

Findings

Entanglement can be generated through correlated vacuum fluctuations.

The light cone divides spacetime into regions with different entanglement mechanisms.

The theory covers regimes from weak to ultrastrong coupling.

Abstract

We propose a simple circuit quantum electrodynamics (QED) experiment to test the generation of entanglement between two superconducting qubits. Instead of the usual cavity QED picture, we study qubits which are coupled to an open transmission line and get entangled by the exchange of propagating photons. We compute their dynamics using a full quantum field theory beyond the rotating-wave approximation and explore a variety of regimes which go from a weak coupling to the recently introduced ultrastrong coupling regime. Due to the existence of single photons traveling along the line with finite speed, our theory shows a light cone dividing the spacetime in two different regions. In one region, entanglement may only arise due to correlated vacuum fluctuations, while in the other the contribution from exchanged photons shows up.