Experimental Demonstration of a Quantum Controlled-SWAP Gate with Multiple Degrees of Freedom of a Single Photon

TL;DR

This paper demonstrates an experimental quantum Fredkin gate using a single photon with multiple degrees of freedom, achieving high conversion efficiency and enabling the creation of entangled states for quantum computing and foundational studies.

Contribution

It introduces a novel implementation of a quantum Fredkin gate in a hybrid single-photon system with high fidelity and explores its capability to generate entangled states exhibiting quantum contextuality.

Findings

Gate conversion rate of 95.4%

Preparation of GHZ-like entangled states

Violation of Mermin inequality confirming quantum contextuality

Abstract

Optimizing the physical realization of quantum gates is important to build a quantum computer. The controlled-SWAP gate, also named Fredkin gate, can be widely applicable in various quantum information processing schemes. In the present research, we propose and experimentally implement quantum Fredkin gate in a single-photon hybrid-degrees-of-freedom system. Polarization is used as the control qubit, and SWAP operation is achieved in a four-dimensional Hilbert space spanned by photonic orbital angular momentum. The effective conversion rate $\mathcal{P}$ of the quantum Fredkin gate in our experiment is $(95.4\pm 2.6)\%$. Besides, we find that a kind of Greenberger-Horne-Zeilinger-like states can be prepared by using our quantum Fredkin gate, and these nonseparale states can show its quantum contextual characteristic by the violation of Mermin inequality. Our experimental design and coding method are useful for quantum computing and quantum fundamental study in high-dimensional and hybrid coding quantum systems.