The Fermi problem with artificial atoms in circuit QED

TL;DR

This paper proposes an experimental test of causality in a 1-D Fermi problem using superconducting qubits, providing a non-perturbative proof that excitation probabilities respect causality despite nonlocal correlations.

Contribution

It introduces a feasible experimental setup with a rigorous non-perturbative proof of causality in a circuit QED model of the Fermi problem.

Findings

Proof of strict causality in the model

Independence of excitation probability until signals arrive

Reconciliation of nonlocal correlations with causality

Abstract

We propose a feasible experimental test of a 1-D version of the Fermi problem using superconducting qubits. We give an explicit non-perturbative proof of strict causality in this model, showing that the probability of excitation of a two-level artificial atom with a dipolar coupling to a quantum field is completely independent of the other qubit until signals from it may arrive. We explain why this is in perfect agreement with the existence of nonlocal correlations and previous results which were used to claim apparent causality problems for Fermi's two-atom system.