A Bipartite Non-Gaussian Entanglement Witness from Conditional Displacement Gates

Abstract: In both circuit and cavity quantum electrodynamics devices where control qubits are dispersively coupled to high quality-factor cavities, characteristic functions of cavity states can be directly probed with echoed conditional displacement (ECD) gates. We propose a method to witness non-Gaussian entanglement between two cavities using ECD gates and readout of the qubit states, which only involves measuring a finite number of points of the characteristic function. Our entanglement witness emerges from an application of Bochner's theorem from harmonic analysis, to a result about the relationship between non-Gaussian entanglement and Wigner negativity.