| In the 1980 s,the combination of quantum mechanics and information science produced a new interdisciplinary subject —quantum informatics,including quantum computing and quantum communication.Among them,quantum computing has become a worldwide research hotspot because of its powerful parallel computing ability,which has great advantages over classical computing in the face of increasing large-scale computing tasks.Quantum logic gate is one of the most basic construction units of quantum computer,and it is a solid foundation for realizing quantum computation.Therefore,it is very important to design a reasonable and feasible quantum logic gate.There are many physical systems to realize quantum logic gates,among which optical systems are favored by researchers because of their many advantages,These advantages include that photons are insensitivity to outside influences,photons can be easily combined with beam splitters,and linear optical devices can be easily obtained.However,it is difficult for photons to interact with each other,which becomes the bottleneck of constructing quantum logic gates by linear optics.The appearance of Kerr medium breaks this bottleneck,it can cause the weak cross Kerr nonlinearity effect between photons passing through it.Therefore,the optical quantum logic gates based on the weak cross Kerr medium have become a focus topic.In this paper,a double-bit controlled non-gate and three-bit Toffoli gate are proposed by using this scheme.The probability of realizing these two kinds of gates is almost 100%,no auxiliary photons are needed,the structure is simple,and it can be realized with current technology.This paper consists of the following five parts:In the first chapter,the brief introduction of quantum computer and the research progress of quantum computer at home and abroad are introduced.The research significance of optical quantum logic gates based on weak cross-Kerr medium is summarized.Finally,the structure arrangement of this paper is given.The second chapter introduces the preliminary knowledge of constructing quantum logic gates,including quantum bits,quantum entanglement,quantum non-cloning theorem,linear optical elements,Cross Kerr Effect in KerrMedium,quantum non-destructive measurement and commonly used quantum logic gates.In the third chapter,a two-bit controlled-NOT gate based on Kerr nonlinearity effect is proposed,the detailed implementation process of the controlled-NOT gate is given,the misjudgment rate of the controlled-NOT gate is analyzed,and some problems in this scheme are analyzed and discussed.Finally,the scheme is summarized.The last chapter summarizes the whole paper and looks forward to the next research direction. |
