| Quantum information science as an interdisciplinary,is a collection of quantum mechanics,information science,computer science,materials science and other new scientific fields.The most basic resource of quantum information is quantum bits,and its transmission quality plays a vital role in the realization of quantum communication and quantum computing,so finding a good transport quantum bit channel becomes a critical problem.The ideal channel for long-range quantum bit transmission is fiber,and for short-range quantum bit transmission,researchers tend to use spin-chain channels.The spin chain channel has a great advantage over other channels.For example,in quantum communication,the spin chain channel avoids the link between the quantum device and the fiber.In terms of quantum computing,the spin chain channel does not require the function of "on" and "off" between the spin,and the realization of this function is a big problem in the practical application of quantum computers.In addition,the spin chain channel does not need to apply additional field mediation(which is very important for quantum computation),the solution is simple and the material is easy to obtain,such as electrons,ion beams,optical arrays,guided atoms,etc.can be used to construct Spin chain channel.Since the spin chain channel scheme has the above advantages,the spin chain channel becomes the ideal linker between the quantum computer devices.For the transmission scheme of quantum state on one-dimensional spin chain channel,people have done a lot of research,focusing on improving the accuracy of transmitting quantum bits,increasing the transmission distance,simplifying the transmission scheme and so on.Based on the above purpose,people have proposed a multi-spin coding scheme with no adjustment of the same coupling constant spin chain,auxiliary spin chain,changing the spin chain structure and adjusting the coupling strength between the spin and the initial quantum state.These programs have their own advantages and disadvantages,this article will make them one by one to introduce.Compared with the one-dimensional spin chain channel quantum state transmission scheme,there is little research on the transmission of quantum state in two-dimensional and three-dimensional spin network.Taking into account the two-dimensional,three-dimensional spin network channel is easier to prepare in practice,and thus more potential practical value,so how to improve the quality of high-dimensional quantum state transmission has become a key research topic.Although the quantum state can be in some special size of the two-dimensional spin network channel to achieve perfect transmission,but these special size of the spin network is very small,practical limited.On the other hand,the fidelity decreases drastically with the increase in the size of the spin network channel,which is very disadvantageous for the transmission of quantum information.In order to realize the high fidelity transmission of quantum state in a kind of special state coding scheme in one-dimensional spin chain channel,we also do a kind of special state coding process on the quantum state in two-dimensional quantum channel in order to improve the two-The transmission quality of the chain channel.We study the transmission of the coded quantum states in a two-dimensional XY-type spin-over network without regulation of the same coupling constant.It is found that although the fidelity of most different number of sub-bit coding states decreases sharply with the increase of the size of the spin wire,there are always some special size spin networks that can transmit the quantum state perfectly,that is,fidelity F = 1,Or height close to 1.For example,for an × spin network,two quantum bit codes are used,and when N = 7,perfect transmission is achieved.And the use of three quantum bit code and four quantum bit coding,respectively,when N = 8,9 and N = 9,11,to achieve perfect transmission.It can also be seen that the size of the perfect transmission channel increases as the number of coded quantum states increases,which gives us a useful idea for studying the high-fidelity transmission scheme of quantum information in high-dimensional spin network Inspired.In contrast to the singularity of the transmission direction of the quantum state in the one-dimensional spin chain channel,the coding quantum state is not unique in the two-dimensional channel,but can have multiple directions.We select two special transmission directions in the two-dimensional spin network channel,namely the edge direction and the diagonal direction,respectively,we study the transmission of the coded quantum state along these two directions.The results show that,regardless of the direction,fidelity with the size of the spin net increases sharply lower,but the diagonal direction of the fidelity is greater than the edge of the fidelity,which is not encoded quantum state in two The transmission quality of the spin network channel is consistent.We also consider the effect of the applied magnetic field on the transmission quantum state.For the quantum state only in the small size of the spin net in the perfect transmission of the situation,we first proposed to be able to perfect transmission of small-size square spin network in a special way spliced into a spin network to improve the long-distance quantum state transmission quality Program.In this paper,we consider the transmission of the quantum state in the spin band in the diagonal direction and the edge direction.It is found that the spin-net band spliced in the diagonal direction can achieve the perfect transmission of the quantum state under the condition that the size is not very large,but the fidelity decreases with the further increase of the spin size.But for the edge along the direction of the splicing of the spin band,the quantum state in the direction of the line to achieve a perfect transmission.We also study the transmission of quantum states in these two types of spin-band networks under a special state coding scheme.It is found that the coded quantum state can improve the quality of quantum state transmission.Therefore,we can choose the special form of spin-band and a special type of coding scheme to improve the transmission quality of quantum states in two-dimensional spin networks. |
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