Figure 1
From: Experimental demonstration of a quantum shutter closing two slits simultaneously
(a) Schematic for the AV03 protocol with two slits. 
is the photonic state propagating in mode i. 
is the state of a probe photon where the photon passes through the slit i. 
is the photonic state reflected by the shutter at slit i. 
is the state of the shutter at the place i. (b) Photonic quantum router (PQR). A nonlinear sign shift (NS) gate is embedded in a Mach-Zehnder interferometer. BS: beam splitter. (c) Photonic scheme using the PQRs for implementing the AV03 protocol. 
is the photonic state of the shutter photon propagating in mode i. SPD: single-photon detector. (d) Linear optical (LO) NS gate. The reflectance of the partially polarizing beam splitter (PPBS) for horizontally and vertically polarized photons is 1/3 and 1, respectively. The transmittance of the circular PPBS (C-PPBS) for horizontally and vertically polarized photons is 1 and 1/3, respectively20. (e) Photonic circuit for the scheme shown in (c) using linear optics NS gates. HWP: half-wave plate; PP: phase plate.
