Quantum interference between light sources separated by 150 million kilometers

TL;DR

This experiment demonstrates quantum interference, entanglement, and nonlocality between photons from sources separated by 150 million kilometers, including the Sun and a quantum dot, revealing quantum effects at astronomical distances.

Contribution

First demonstration of quantum interference and entanglement between dissimilar light sources separated by astronomical distances, including the Sun and a quantum dot.

Findings

Observed two-photon interference with 0.796 visibility

Demonstrated post-selected entanglement with 0.826 fidelity

Violated Bell's inequality by 2.20

Abstract

We report an experiment to test quantum interference, entanglement and nonlocality using two dissimilar photon sources, the Sun and a semiconductor quantum dot on the Earth, which are separated by 150 million kilometers. By making the otherwise vastly distinct photons indistinguishable all degrees of freedom, we observe time-resolved two-photon quantum interference with a raw visibility of 0.796(17), well above the 0.5 classical limit, providing the first evidence of quantum nature of thermal light. Further, using the photons with no common history, we demonstrate post-selected two-photon entanglement with a state fidelity of 0.826(24), and a violation of Bell's inequality by 2.20(6). The experiment can be further extended to a larger scale using photons from distant stars, and open a new route to quantum optics experiments at an astronomical scale.