From "Interferometric imaging of amplitude and phase of spatial biphoton states" (2023) <a href="https://www.nature.com/articles/s41566-023-01272-3" rel="nofollow noreferrer">https://www.nature.com/articles/s41566-023-01272-3</a> :<p>> [...] <i>The number of projective measurements necessary for a full-state tomography scales quadratically with the dimensionality of the Hilbert space under consideration [2]. This issue can be tackled with adaptive tomographic approaches [3,4,5] or compressive techniques [6,7], which are, however, constrained by a priori hypotheses on the quantum state under study. Moreover, quantum state tomography via projective measurement becomes challenging when the dimension of the quantum state is not a power of a prime number [8]. Here we try to tackle the tomographic challenge, in the specific contest of spatially correlated biphoton states, looking for an interferometric approach inspired by digital holography [9,10,11], familiar in classical optics. We show that the coincidence imaging of the superposition of two biphoton states, one unknown and one used as a reference state, allows retrieving the spatial distribution of phase and amplitude of the unknown biphoton wavefunction. Coincidence imaging can be achieved with</i> [... Quantum Imaging]