Correction to: Nature Photonics https://doi.org/10.1038/s41566-021-00867-y, published online 27 August 2021

In the version of this News & Views initially published, in the third sentence of the fourth paragraph, in the sentence reading “For a two-particle system one has \(\left| {\chi _1,\chi _2} \right\rangle = e^{\phi _{{{{\mathrm{ex}}}}}}\left| {\chi _2,\chi _1} \right\rangle\),” the letter “i” was missing from “\(e^{\phi _{{{{\mathrm{ex}}}}}}\)” and has been corrected to read: “\(e^{i\phi _{{{{\mathrm{ex}}}}}}\).” In the sixth paragraph, in the sentence reading “The quantum interference part of the set-up especially creates the quantum superposition \(\left| \psi \right\rangle = \left| {{{{\mathrm{ref}}}}\;{{{\mathrm{state}}}}} \right\rangle + \left| {{{{\mathrm{exc}}}}\;{{{\mathrm{state}}}}} \right\rangle = e^{i\varphi _{{{{\mathrm{ref}}}}}}\left| { \leftrightarrow _{{{\mathrm{a}}}}, \updownarrow _{{{\mathrm{b}}}}} \right\rangle + e^{i\phi }\left| { \leftrightarrow _{{{\mathrm{d}}}}, \updownarrow _{{{\mathrm{c}}}}} \right\rangle\), where φref is an adjustable phase,” after the word “where,” the symbol “φref” was missing, but has been restored as shown here.

These changes have been made to the online version of this News & Views.