quantum measurement

Researchers at the National Institute of Standards and Technology (NIST), JQI and the Department of Physics at the University of Maryland have devised and demonstrated a system that could dramatically increase the performance of communications networks while enabling record-low error rates in detecting even the faintest of signals. The work could potentially decrease the total amount of energy required for state-of-the-art networks by a factor of 10 to 100.

In an arranged marriage of optics and mechanics, JQI-NIST physicists have created microscopic structural beams that have a variety of powerful uses when light strikes them. Able to operate in ordinary, room-temperature environments, yet exploiting some of the deepest principles of quantum physics, these optomechanical systems can act as inherently accurate thermometers, or conversely, as a type of optical shield that diverts heat. .Described in a pair of new papers in Science and Physical Review Letters, the potential applications include chip-based temperature sensors for electronics and biology that would never need to be adjusted since they rely on fundamental constants of nature; tiny refrigerators that can cool state-of-the-art microscope components for higher-quality images; and improved “metamaterials” that could allow researchers to manipulate light and sound in new ways.

From NIST-PML — Precise measurements of optical power enable activities from fiber-optic communications to laser manufacturing and biomedical imaging — anything requiring a reliable source of light. This situation calls for light-measuring (radiometric) standards that can operate over a wide range of power levels.
Currently, however, different methods for calibrating optical power measurements are required for different light levels. At high levels, existing radiometric standards employ analog detectors, diodes that generate a current proportional to the incident light intensity, but become imprecise at low levels. Low-power detectors, by contrast, very accurately measure discrete (usually very small) numbers of photons, but cannot handle light at higher levels. Because of the incommensurate scales and incompatible technologies, comparison between the two kinds of measurements isn't easy, resulting in long calibration chains to span the difference.
Linking standards for widely different powers requires extending the dynamic range of detection to cover the region between the two measurement regimes. There are two options for bridging this gap: a "top-down" approach using analog detectors and a "bottom-up" method that starts with counting individual photons.
Exploring the second option, a team of scientists from NIST's Physical Measurement Laboratory (PML) has demonstrated a technique for extending the range of photon-counting detectors by employing optical attenuators, devices that block controlled fractions of incoming light. The results, recently published in Optics Express, could lead to improved standards to cover a much wider range of optical power.

At low light, cats see better than humans. Electronic detectors do even better, but eventually they too become more prone to errors at very low light. The fundamental probabilistic nature of light makes it impossible to perfectly distinguish light from dark at very low intensity.  However, by using quantum mechanics, one can find measurement schemes that can, at least for part of the time, perform measurements which are free of errors, even when the light intensity is very low.