Light is known to have a number of fundamental properties, including color, brightness, and direction, most of which are immediately apparent and can be observed with the naked eye. There are now several instruments to detect and measure these properties, such as photon counters, detectors often used in research that measure brightness by counting individual light quanta. Crucially, some existing devices can also measure these properties at the so-called quantum limit, which is a fundamental barrier for the precision of a measurement.
Click here for original story, A method to perform canonical phase measurements using quantum feedback
Source: Phys.org