Twisted light increases polarization measurement sensitivity

Ars Technica : Measuring changes in the polarization of one half of a split beam of photons is a common and sometimes challenging task in many experiments. Entangling the photons increases the sensitivity of the measurement, but it is not easy to entangle more than a relatively small number of photons. Now, an international group of researchers has developed a method that matches the sensitivity of the entangled photons but isn’t limited by the beam’s intensity. Their technique uses twisted light. Although polarized light normally has an electric field with no orbital angular momentum, it is possible to give it a “twist,” creating a corkscrew-like electric field. If the light is twisted after it has run through an experiment, any change to its original linear polarization is magnified at a rate proportional to the amount of orbital angular momentum the light has been given. The increased sensitivity is likely to be most useful for measuring small changes in polarization.