Quantum controlled-Z gate for weakly interacting qubits

TL;DR

This paper presents a new scheme for implementing a maximally entangling controlled-Z gate between weakly interacting qubits, using quantum interference to enhance coupling, demonstrated experimentally with linear optics.

Contribution

The authors introduce a universal method to implement a controlled-Z gate for weakly interacting qubits via quantum interference, verified experimentally with photons.

Findings

Successfully demonstrated the scheme with linear optical setup.

Proved the method's applicability to various physical platforms.

Showed enhancement of interqubit coupling through quantum interference.

Abstract

We propose and experimentally demonstrate a scheme for implementation of a maximally entangling quantum controlled-Z gate between two weakly interacting systems. We conditionally enhance the interqubit coupling by quantum interference. Both before and after the interqubit interaction, one of the qubits is coherently coupled to an auxiliary quantum system, and finally it is projected back onto qubit subspace. We experimentally verify the practical feasibility of this technique by using a linear optical setup with weak interferometric coupling between single-photon qubits. Our procedure is universally applicable to a wide range of physical platforms including hybrid systems such as atomic clouds or optomechanical oscillators coupled to light.