Direct test of the “quantum vampire’s” shadow absence with use of thermal light

The counterintuitive nature of quantum physics leads to a number of paradoxes. One of them is a “quantum vampire” effect [Fedorov et al., Optica 2, 112 (2015) ], which means that the photon annihilation in a part of a large beam does not change the shape of the beam profile (i.e., does not cast a shadow), but it may change the total beam intensity. Previously, this effect was demonstrated just in a simplified double-mode regime [Fedorov et al., Optica 2, 112 (2015), Katamadze et al., Optica 5, 723 (2018) ]. In this Letter, a direct test of shadow absence after the photon annihilation was performed using the thermal state of light at the input.