Fig. 1
From: Observation of emergent momentum–time skyrmions in parity–time-symmetric non-unitary quench dynamics
Experimental setup for detecting momentum–time skyrmions in non-unitary QWs. Photons are generated via spontaneous parametric down conversion through a Type-I non-linear β-barium-borate (BBO) crystal. The single signal photon is heralded by the corresponding trigger photon and can be prepared in an arbitrary linear polarization state via a polarizing beam splitter (PBS) and wave plates. Conditional shift operation S and coin rotation R are realized by a beam displacer (BD) and two half-wave plates (HWPs), respectively. For non-unitary QWs, a sandwich-type HWP–PPBS–HWP setup is inserted to introduce non-unitarity, where PPBS is an abbreviation for partially polarizing beam splitters. Two kinds of measurements, including projective measurements and interference-based measurements, are applied before the signal and heralding photons are detected by avalanche photodiodes (APDs)
