Quantum Sensors: Improved Optical Measurement via Specialized Quantum States

Figure 4

Schematic of setup for super-resolution angular displacement measurements using entangled OAM states. Spontaneous parametric downconversion in a nonlinear crystal (on the left) sends entangled photon pairs into a Mach-Zehnder interferometer (middle portion) which contains a Dove prism in one arm. On the right, photodetectors are connected to a coincidence circuit, so that an event is registered only when both detectors fire within a short time window.