I personally understand and use language to describe how quantum cryptography communication technology is realized. Because quantum mechanics is too difficult for ordinary people, even if Einstein's name is planted in these phenomena, I don't have a professional knowledge background, so this paper will try not to touch the theory of quantum mechanics itself, and try to ensure that all the phenomena and principles discussed later will not be too profound, so it can be understood by graduate students in science and engineering.
Before formal notification, the first thing to be standardized is a typical quantum and photon polarization characteristic. Optical polarization filters should be familiar to everyone. For example, when glasses are used in 3 d movies, light with different polarization directions can only be filtered out by filters, or light with a specific polarization direction. This application will use the cross filter, and the filter settings are divided into two angles, namely+filter and X filter. +filters are the same vertical.
Sometimes it can pass through this+-type filter, sometimes it can't, and it can be expressed by photons. The polarization direction angle is different according to polarization, and sometimes it will be crossed, vertical, uncertain or even filtered.
Similarly, the X-type filter rotates the+-type filter by 45 degrees, so that the polarization state of tilted photons can pass through, and can leave the oblique angle by 45 degrees (-) or +45 degrees. So when a horizontal or vertical photon passes through the X-type filter, you can't be sure whether it will turn left or right or not.
In this way, we will have at least two measurement filter setting modes. Finally, how can we detect whether the polarization direction of photons is 0? Somehow, we can specify that the cross is 0, and when it is set to 1, we can specify that the left diagonal is 0 and the right diagonal is 1, that is, we are neither vertical nor horizontal nor oblique after filtering, but we can use it to represent 0 and 65438+ anyway.
In addition, I also emphasize that technically, you can now set a filter to randomly switch between two angles. In application, instead of a group of measurement photons, the placement angles of the filters can form a random sequence. For example, the filter bank sequence used for group measurement is ++x++x, and the next group measurement becomes * *++. In short, it is irregular, which is also the need of encryption technology.