Greenberger-Horne-Zeilinger generation protocol for N superconducting transmon qubits capacitively coupled to a quantum bus

TL;DR

This paper presents a protocol for generating GHZ entangled states among N superconducting transmon qubits coupled via a quantum bus, using a controllable effective Hamiltonian in circuit QED.

Contribution

It introduces a new method to produce multi-qubit GHZ states in superconducting circuits with homogeneous coupling and analyzes its robustness and entanglement properties.

Findings

GHZ states generated within a time scale of inverse effective coupling

Protocol is robust to parameter inhomogeneities

Method enables probing of non-local and genuine multipartite entanglement

Abstract

We propose a circuit quantum electrodynamics (QED) realization of a protocol to generate a Greenberger-Horne-Zeilinger (GHZ) state for $N$ superconducting transmon qubits homogeneously coupled to a superconducting transmission line resonator in the dispersive limit. We derive an effective Hamiltonian with pairwise qubit exchange interactions of the XY type, $\tilde{g}(XX+YY)$, that can be globally controlled. Starting from a separable initial state, these interactions allow to generate a multi-qubit GHZ state within a time $t_{\text{GHZ}}\sim \tilde{g}^{-1}$. We discuss how to probe the non-local nature and the genuine $N$-partite entanglement of the generated state. Finally, we investigate the stability of the proposed scheme to inhomogeneities in the physical parameters.