Today, information science plays an amazing role in promoting progress in social civilization and improving human life. As humans increase the increasing information demand, people are constantly advancing the development of information technology, but the functionality of the existing information system is close to the limit. Over the past 30 years, the number of transistors integrated on each chip increases with time, which is known as molar law, indicates that computer storage units will be a single atom, and electronics in the circuit after more than 10 years. The behavior will no longer obey the rules of classic mechanics, and replaced by quantum mechanics. So what is the problem of quantum effects affecting computer operations. Therefore, further development of information science must be used in new principles and new methods. Since the quantum characteristics have a unique function in the field of information, it may break through the limit of the existing classical information system in improving the operation speed, ensuring information security, increasing information capacity, and improvement accuracy, and thus quantum power is first in information science. Applications, a new discipline branch - quantum information is also delivered. The discipline is the product of quantum mechanics and information science. It is based on the state of quantum mechanics, and the research information processing is a new frontier science. Quantum informationics include several squares such as quantum cryptography, quantum communications, quantum computers, have achieved significant breakthroughs in theory and experiment in recent years.
Quantum computer
Quantum computers are a physical device that follows the quantum mechanics to perform high speed mathematics and logic operations, store and process quantum information. When a device processing and calculate quantum information, it is a quantum computer when the quantum algorithm is run. The concept of quantum computers is derived from research on reversible computers. The purpose of studying the reversible computer is to solve the problem of energy consumption in the computer. From the 1960s to the 1970s, people found that energy consumption caused the chip heating in the computer, which greatly affected the integration of the chip, thus limiting the operating speed of the computer. The study found that energy consumption originates from irreversible operations during the calculation process. So, whether the calculation process must use irreversible operation to complete? The answer to the problem is that all classic computers can find a corresponding reversible computer and do not affect the capacity. Since each of the operations in the computer can be transformed into reversible operation, in quantum mechanics, it can be referred to by a neighbor. Early quantum computers actually use the classic computer described in quantum mechanics, and there is no use of quantum mechanics, such as stacking and coherence of quantum state. In a classic computer, the basic information unit is bits, and the calculation pair is a variety of bit sequences. Similarly, in the quantum computer, the basic information unit is quantum bit, and the calculation pair is the quantum bit sequence. Even, the quantum bit sequence can not only be in the superposition state of various orthogonal states, but also in an entangled state. These special quantum states not only provide the possibility of quantum parallel, but will also bring many wonderful properties. Unlike classic computers, quantum computers can make arbitrary positive transformations, after the output state is obtained, the measurement results in the calculation result. Therefore, quantum calculations make great expansion of classic computing, in mathematical form, classic calculations can be considered as a particular quantum calculation. The quantum computer transforms each superposition, all of which is completed simultaneously, and superimposed on a certain probability, which is given, which is called quantum parallel. In addition to performing parallel calculations, another important purpose of quantum computers is analog quantitative subsystem, which is unable to be classic. Whether it is quantum parallel calculation or quantum simulation calculation, quantum coherence is used in nature. Unfortunately, quantum coherence in the actual system is difficult to keep. In quantum computers, quantum bits are not an isolated system, which interacts with external environments, resulting in the decay of quantum coherence, that is, dry. Therefore, to make quantum calculations become reality, a core problem is to overcome the coence. Quantum coding is the most effective way to overcome coincidence that has been discovered so far. The main number of quantum coding schemes are: quantum error correction code, quantum avoidance code and quantum anti-wrong code. Quantum error correction code is a classic error correction code, which is the most class of codes in the current research. Its advantages are wide range, and the disadvantage is not high. So far, there is no quantum computer in the world. However, many laboratories around the world are pursuing this dream with huge enthusiasm. How to implement quantum calculations, the plan is quite, the problem is that the manipulation of the microscopic amount is really too difficult in the experiment. The currently proposed scheme mainly utilizes atomic and light cavity interactions, cold traps binds ions, electron or nuclear spin resonance, quantum point manipulation, superconducting quantum interference, and the like. It is still difficult to say which solution is more prospects, just quantum dot programs and superconducting Joseph knot solutions are more suitable for integration and miniaturization. In the future, there may not be an existing plan, and finally stand out and stand out is a new design, and this new design is based on a new material, just like a semiconductor material. The purpose of studying quantum computers is not to use it to replace existing computers. Quantum computers make the computational conceptual concept, which is the difference between the quantum computer and other computers such as optical computers and biocomputers.
The role of quantum computer is far more than solving problems that some classic computers cannot solve. Quantum communication
The basic components of the quantum communication system include quantum generators, quantum channels, and quantum measuring devices. According to the information it transmits, it is classic or quantum. The former is mainly used for the transmission of quantum keys, which can be used for quantum invisible pathways and quantum entangled distribution. The so-called invisible transmission refers to a "complete" information transmitted by the real thing. From the physics perspective, you can imagine the process of invisible transmission: first extract all the information of the original, then transfer this information to the receiving place, the recipient is based on this information, select the basic unit of the same as the composition, manufactured The perfect replica of the original. However, the uncertainty principle of quantum mechanics does not allow all information of the protocol to accurately extract the stock, which cannot be perfect. So long-term, invisible transmission is just a fantasy. In 1993, 6 scientists from different countries proposed a method of using a classical and quantum to achieve quantum stealth transmission mode: transfer the unknown quantum of a particle to another, prepared another particle to On the quantum state, the original particles remain in place. Its basic idea is to divide the information of the original information into two parts of the classical information and quantum information, which are transmitted to the recipient via a classic channel and quantum channel. The classic information is obtained by a sender to perform some measurement of the original, and quantum information is the remaining information that the sender is not extracted in the measurement; the recipient can prepare the original quantum state. replica. This process is only the quantum state of the original, rather than the original itself. The sender can even know anything about this quantum state, and the recipient is in the quantum state of other particles in the original. In this program, the unactivated domain of entanglement plays a crucial role. Quantum mechanics is non-domain theory, which has been confirmed by the experimental results of Bell inequality, so quantum mechanics show many anti-intuitive effects. Two particle states can be prepared in such a manner in such a manner, and the association between them cannot be explained in a class, such a statement is a entangled state, and the quantum entangled is between two or more quantum systems. Non-domain non-classic associations. The quantum invisible path is not only important to people's mystery and disclose the mystery law in the physics, but also use quantum state as an information carrier. The transmission of large capacity information is completed by the transmission of the quantum state, and the quantum is realized in principle. Secret communication. In 1997, China Youth Scholars in Austria had cooperated with Dutch scholars and et al., The first time I realized remote transmission of unknown quantum states. This is the first time in the experiment successfully transmitted a quantum state from the photons from A to a photon. The "state" transmitted in the experiment is only "state" of the quantum information, and the photon itself as the information is not transmitted. Recently, Pan Jianwei and its partners have achieved a new breakthrough in the study of how high quality quantum entangled states. In order to carry out long-distance quantum type invisible transmission, it is often necessary to have a maximum quantum entanglement state in advance to distant two places. However, due to the existence of various inevitable environmental noise, the quality of quantum entanglement is getting worse as the transmission distance increases. Therefore, how to purify high quality quantum entanglement is an important topic in the current quantum communication research. In recent years, many research teams in the international research team have been studied in this topic and proposed a series of quantum entangled state purification, but no one can be implemented in existing technologies. Recently, Pan Jianwei discovered the theoretical solution that utilizes prior art in experimental quantum entangled state purification, in principle, in principle, in principle, in principle, in principle, the fundamental problem in which current quantum communications is currently solved. The results of this research were highly evaluated by the international scientific community, known as "a leap in the scales of quantum communication research."
Quantum cryptography
Quantum cryptography is a product of cryptography and quantum mechanics, which utilizes the quantum properties of the system. First, I think that the quantum is physically used for cryptosome is the American scientist Wisner. Wisner proposed in 1970 that a single quantum state manufactured unable to manufacture unable to make an electronic banknote. But this envisaged implementation takes a long time to save the single quantity, not realistic. Bennet and Brassad have found in research, although the single quantity is not well saved but can be used for transmission information. In 1984, Bennet and Brazard proposed the first quantum cryptographic scheme, called the BB84 program, which ushered in the new period of quantum cryptography. In 1992, Benedit also proposed a simple, but efficient program, that is, the B92 program. Quantum cryptography is not used to transmit ciphertext, but is used to establish, transfer password book. According to the uncertainty principle of quantum mechanics and the quantum non-cloning theorem, the existence of any stealing person will be discovered, thereby ensuring the absolute security of the password book, but also guarantees the absolute security of encrypted information. The initial quantum password communication utilizes the polarization characteristics of the photon, and the current mainstream experiment scheme is encoded with the phase characteristics of the photon. Currently, the fastest countries develop in the quantum cryptography experiments are the United Kingdom, Switzerland and the United States. The British National Defense Research Department first implemented the phase coding quantum key distribution based on the BB84 program in 1993, and the fiber transmission length was 10 km. The study was later turned to the British Communication Laboratory. By 1995, it has been successfully achieved in 30 kilometers long fiber transmission. The quantum key distribution is successfully achieved. The advantage of phase-coding is less demanding than polarization coding. In long-distance fiber transmission, the polarization of light will degenerate, resulting in an increase in the error rate. However, Switzerland Geneva's polarization coding scheme based on the BB84 program in 1993, transmitting 1.3 micron wavelength photons in 1.3 km long fibers, and the error rate is only 0.54%, and in 1995 in the end of the Lake Geneva The 23 km long civil communication fiber optic cable is laid, and the error rate is 3.4%. In 1997, they used Faraday to eliminate the influencing factors such as birefringence in fibers, so that the stability and convenience of the system are greatly improved, called "plug and play" quantum code scheme. The American Los Aramos National Lab has created a new record of quantum password communication distance in the fiber. They use similar English experimental devices, through advanced electronic means, successfully transferring quantum keys in an underground fiber optic cable up to 48 kilometers in an underground fiber optic cable, while they have successful in free space. In 1999, Sweden cooperated with Japan to successfully carry out 40 kilometers of quantum password communication experiments in optical fibers. In China, the research of quantum password communication has just started, and the Chinese Academy of Sciences has made a demo experiment in China in 1995, and East China Normal University has used the B92 program, but also in a shorter free space. of. In 2000, the Physics of the Chinese Academy of Sciences and the graduate institute cooperated to complete 1.1 kilometers of quantum password communication presentation experiments in a single-mode fiber of 850 nm. In general, my country has a big gap between China. The research progress of quantum mechanics has led to the birth of new Xingjiao - the birth of quantum informationistry, showing a beautiful future for information science. On the other hand, the in-depth development of quantum information has encountered many new topics, which in turn strongly promotes the development of quantum mechanics. When the quantum informationology is in theory, the researchers have been more important in theory, so that the researchers have more enthusiasm. However, the practical quantum information system is a quantum system on a macroscopic scale, and people want to effectively prepare and operate the quantum state of this quantum system is still very difficult.
