An ordinary rain gauge collects water in a bucket and shows the total volume of precipitation. But the new device is like a sensitive palm that feels every falling drop and keeps count, even when the drops number in the thousands.
That's exactly what physicists have built. They have learned to precisely count photons, the tiniest packets of light, in very weak laser flashes. Previously, with large numbers of photons, uncertainty inevitably grew: shot noise, akin to random fluctuations in the water level of a bucket in the rain. Here, they managed to 'outshout' this noise by more than two and a half times — by 4.1 decibels — across the entire range from zero to 9000 photons.
To achieve such precision, the scientists performed tomography of the detector — reconstructing its full quantum characterization, described by a matrix with 138 million elements. This is like creating a detailed map of the sensitivity of each of the 1024 channels. As a result, even at 276 photons in a single flash, the error does not exceed one photon.
With a flash rate of 80,000 times per second, the device measures light power of about 71 picowatts — hundreds of billions of times weaker than a pocket flashlight bulb. Such a detector blurs the line between counting single photons and conventional power meters, paving the way for new standards of precision in optics.
The 71 picowatts measured by the device is roughly the power of light from a match located 2000 kilometers away.