Quantum Sensors: Improved Optical Measurement via Specialized Quantum\n States

Classical measurement strategies in many areas are approaching their maximum\nresolution and sensitivity levels, but these levels often still fall far short\nof the ultimate limits allowed by the laws of physics. To go further,\nstrategies must be adopted that take into account the quantum nature of the\nprobe particles and that optimize their quantum states for the desired\napplication. Here, we review some of these approaches, in which quantum\nentanglement, the orbital angular momentum of single photons, and quantum\ninterferometry are used to produce optical measurements beyond the classical\nlimit.\n