Figure 2
From: Demonstrating an absolute quantum advantage in direct absorption measurement
Experimental setup. A 404-nm laser beam pumps a PPKTP crystal to generate SPDC. After removing the pump beam, the two photons (each labeled the signal and idler photons) are separated and launched inside two optical fibres. The output of one fibre is passed through a sample before being focussed onto a few pixels of a CCD camera, while the second fibre output is directly focussed on the camera.
