Accessing electronic entanglement via photo-assisted two-electron tomography

Abstract: Witnessing entanglement between electrons propagating in quantum circuits requires accessing their two-electron coherences, which encode the two-particle quantum correlations generated by Coulomb interactions. Yet, experimental reconstruction of two-electron coherence remains a major challenge. We introduce photo-assisted two-electron tomography, a quantum coherence reconstruction protocol from dc-currents and time-averaged current correlations, routinely measured in electron quantum optics experiments. Driving an energy filter with a small rf tone encodes off-diagonal coherences in the frequency domain into the dc-current response, enabling single-electron tomography without resorting to current-noise measurements. Extending it to two channels, current correlations after two photo-assisted filters reconstruct the two-electron Wigner distribution and isolate its irreducible two-body part. When applied to Coulomb-coupled quantum Hall edge channels, the protocol reveals interaction-induced energy entanglement. Signatures of this entanglement are visible through the violation of an entanglement witness based on Cauchy-Schwarz inequalities, as well as Wigner function negativities, which remain resolved above the thermal background for realistic device parameters. A generalized Franson geometry further extends the approach to intra-channel two-electron coherences. This opens a direct pathway to detect and characterize electronic entanglement in ballistic quantum circuits.