Vogl, TobiasKnopf, HeikoWeissflog, MaximilianLam, Ping KoyEilenberger, Falk2023-05-052023-05-052643-1564http://hdl.handle.net/1885/289891Quantum theory is the foundation of modern physics. Some of its basic principles, such as Born's rule, however, are based on postulates which require experimental testing. Any deviation from Born's rule would result in higher-order interference and can thus be tested in an experiment. Here, we report on such a test with a quantum light source based on a color center in hexagonal boron nitride (hBN) coupled to a microcavity. Our room-temperature photon source features a narrow-linewidth, high-efficiency, high-purity, and on-demand single-photon generation. With the single-photon source we can increase the interferometric sensitivity of our three-path interferometer compared to conventional laser-based light sources by fully suppressing the detector nonlinearity. We thereby obtain a tight bound on the third-order interference term of 3.96(523) x 10(-4). We also measure an interference visibility of 98.58% for our single photons emitted from hBN at room temperature, which provides a promising route for using the hBN platform as light source for phase-encoding schemes in quantum key distribution.This work was funded by the Australian Research Council (Grants No. CE170100012 and No. FL150100019), the Federal Ministry of Education and Research BMBF (Grant No. 13XP5053A), and by the European Union, the European Social Funds and the Federal State of Thuringia (2019FGR0101).application/pdfen-AU© 2021 American Physical Societyhttps://creativecommons.org/licenses/by/4.0/202110.1103/PhysRevResearch.3.0132962022-02-13Creative Commons Attribution 4.0 International License