Establish an ordering strategy for positivity-constrained tomography

Determine whether the tomographic equations for the Wick deviation in the basis of atoms of signal permit a sequential reconstruction and enforcement of positivity constraints analogous to the ordering used in single-electron tomography, with the stationary coherence fixed before the remaining components are reconstructed.

Background

The paper derives explicit necessary positivity conditions for the reconstructed two-electron Wick deviation in a basis of finite-width Floquet atoms of signal. These constraints involve both diagonal and off-diagonal elements of the reconstructed two-particle coherence, while the latter also depend on single-electron data from the first tomography stage.

For single-electron tomography, analogous constraints can be imposed sequentially after independently determining the stationary part through spectroscopy. The paper leaves unresolved whether an analogous ordering is possible for the two-electron tomographic equations.

References

Whether a similar ordering is possible here depends on the structure of the tomographic equations in the basis of atoms of signal, and is left for future work.

— Accessing electronic entanglement via photo-assisted two-electron tomography  (2610.12286 - Paulet et al., 8 Oct 2026) in Appendix, Section “Positivity constraints,” subsection “Single particle atoms of signal”