Is it safe to check the weather using quantum satellite positioning?
Traditional communication relies on electromagnetic waves. Electromagnetic waves propagate in the air, and anyone can obtain the information. In order to solve this problem, a new interdisciplinary subject—quantum communication—has been developed in the past two decades. It is a new research field that combines quantum theory and information theory. Quantum communication has the characteristics of high efficiency and absolute security. The encryption level is higher and it is more difficult to be stolen. Quantum Communication
Quantum Communication refers to a new type of communication method that uses the quantum entanglement effect to transmit information. Quantum communication is a new interdisciplinary subject developed in the past two decades. It is a new research field that combines quantum theory and information theory. Quantum communication mainly involves: quantum cryptographic communication, quantum teleportation and quantum dense coding. This subject has gradually moved from theory to experiment and developed towards practicality. Efficient and secure information transmission has attracted increasing attention. Based on the basic principles of quantum mechanics, quantum communication has the characteristics of high efficiency and absolute security, and has therefore become an international research hotspot in quantum physics and information science.
The basic components of a quantum communication system include quantum state generators, quantum channels and quantum measurement devices. They are divided into two categories according to whether the information they transmit is classical or quantum. The former is mainly used for the transmission of quantum keys, while the latter can be used for the distribution of quantum teleportation and quantum entanglement. The so-called teleportation refers to a "complete" information transmission that is separated from the physical object. From a physical perspective, the process of teleportation can be imagined like this: first extract all the information of the original object, and then transmit this information to the receiving location. Based on this information, the recipient selects the same basic units that make up the original object, and creates A perfect replica of the original. However, the uncertainty principle of quantum mechanics does not allow precise extraction of all information about the original, and this copy cannot be perfect. So for a long time, teleportation was little more than a fantasy.
In 1993, six scientists from different countries proposed a plan to use a combination of classical and quantum methods to achieve quantum teleportation: transmit the unknown quantum state of a particle to another place. Another particle is prepared into the quantum state, while the original particle remains in place. The basic idea is to divide the original information into two parts: classical information and quantum information, which are transmitted to the receiver via classical channels and quantum channels respectively. Classical information is obtained by the sender performing some kind of measurement on the original object, and quantum information is the remaining information that the sender did not extract during the measurement; after the receiver obtains these two kinds of information, he can prepare a complete quantum state of the original object. replica. What is transmitted in this process is only the quantum state of the original object, not the original object itself. The sender may not even know anything about this quantum state, while the receiver places other particles in the quantum state of the original object.
In this scheme, the non-locality of the entangled state plays a crucial role. Quantum mechanics is a non-local theory, which has been confirmed by experimental results that violate Bell's inequality. Therefore, quantum mechanics exhibits many counter-intuitive effects. In quantum mechanics, two particle states can be prepared in such a way that the correlation between them cannot be explained classically. Such a state is called an entangled state. Quantum entanglement refers to the relationship between two or more quantum systems. Non-local and non-classical correlations. Quantum teleportation is not only of great significance in the field of physics for people to understand and reveal the mysterious laws of nature, but also can use quantum states as information carriers to complete the transmission of large-capacity information through the transmission of quantum states, achieving in principle undecipherable quantum information. Confidential Communications. In 1997, Pan Jianwei, a young Chinese scholar studying in Austria, collaborated with Dutch scholar Bomister and others to realize the long-distance transmission of unknown quantum states for the first time. This is the first time in the world that a quantum state has been successfully transmitted experimentally from a photon in place A to a photon in place B. What is transmitted in the experiment is only the "state" that expresses quantum information, and the photons themselves, which are the information carriers, are not transmitted. In order to carry out long-distance quantum state teleportation, it is often necessary to allow two places that are far apart to have the maximum quantum entanglement state in advance. However, due to the existence of various inevitable environmental noises, the quality of quantum entangled states will become worse and worse as the transmission distance increases. Therefore, how to purify high-quality quantum entangled states is an important topic in quantum communication research.
Many international research groups are studying this topic and have proposed a series of theoretical solutions for the purification of quantum entangled states, but none of them can be realized using existing technology. Pan Jianwei and others discovered a theoretical solution for the purification of quantum entangled states that is experimentally feasible using existing technology, and in principle solved the fundamental problem in long-distance quantum communication. This research result has been highly praised by the international scientific community and is called "a leap forward in long-distance quantum communication research."