Classical entanglement in polarization metrology
  Quantum approaches relying on entangled photons have been recently proposed to increase the efficiency of optical measurements. We demonstrate here that, surprisingly, the use of classical light with entangled degrees of freedom can also bring outstanding advantages over conventional measurements in polarization metrology. Specifically, we show that radially polarized beams of light allow to perform real-time single-shot Mueller matrix polarimetry. Our results also indicate that quantum optical procedures requiring entanglement without nonlocality can be actually achieved in classical optics regime. 
Falk T\"oppel, Andrea Aiello, Christoph Marquardt, Elisabeth   Giacobino, Gerd Leuchs
quant-ph physics.optics