Fig. 1: Experimental concept and setup.
From: Quantum steering with vector vortex photon states with the detection loophole closed
a Conceptual diagram of vector vortex steering. b Experimental setup. A photon-pair source6,37 produces a polarization-entangled singlet state. The polarization qubit of one photon is converted to a vector vortex state qubit through a q-plate and is sent through a free-space channel (4F imaging system not shown) to Bob. Alice’s measurement apparatus performs a two-outcome projective measurement on a polarization qubit. c Bob’s measurement apparatus has an additional q-plate that converts a vector vortex state qubit into a polarization qubit, and is mounted in a cage system in order to allow for a rotation around the beam propagation axis, as described in the main text. Blue and green backgrounds represent untrusted and trusted devices, respectively.
