Implementation Of Quantum Logic Gates And Quantum Dense Coding Based On Optical System

Quantum theory and relativity are created by people in the early twentieth century, and it is established initially to explain some phenomenon, such as blackbody spectrum, the structure of atomic and nuclear, electrodynamics phenomena of moving objects and so on, while quantum information is a branch of quantum theory. The mysteries of quantum information science have been gradually opened; actually, it is the product of combining of quantum mechanics and information science. Quantum mechanics theory has been widely and successfully implemented in diverse fields, such as, informatics, physics, and medical science and so on. Quantum information mainly includes fields of quantum communication and quantum computing:quantum communication researches quantum cryptography, quantum teleportation, long distance quantum communications technology and so on; quantum computing researches quantum computer and quantum algorithm which are located in the service of a quantum computer. Quantum computer, quantum cryptography and quantum transmission are the most valuable ideas in quantum information science, and they have gradually stood out from this new field.The realization of quantum communication and quantum computing needs not only entanglement source, but also needs a quantum information processor for carrying information. Actually, people utilize a variety of micro physical systems act as quantum information processor. Quantum bit (qubit) is the foundation of quantum information unit. Qubit can carry all kinds of quantum information and be handled to finish calculation and information transmission. An important topic in quantum information science is to find the suitable micro physical systems, as well as schemes which have strong feasibility and high success probability. At present, the commonly used quantum system in information processing is optical system, quantum dots, optical cavity QED system and nuclear magnetic resonance (NMR) system and so on. We are aware that the photon is remarkably characterized by high speed transmission and low noise. Besides, easily be preparation and transported is also the advantage of optical system. So, optical system is considered as one of the best candidate systems in the field of long distance quantum state teleportation. Optical system has also achieved faster development in the experiment. So it will be a very promising research subject for the use of the optical system in realizing quantum information processing.In our paper, the main content are realization of multi-particle quantum logic gates in the optical system, and implementation of quantum dense coding in the system of weak cross- Kerr medium-cavity QED system with his help of quantum entanglement state. Our achievements as follows:1. The realization of multi-particle quantum logic gate in the optical system.We first designed a two-particle controlled NOT (CNOT) gate, on the basis of which we achieve the optical Toffoli gate scheme. By using the linear optical elements, cross-Kerr nonlinearity effect and quantum non destructive measurement detection (QND), our scheme’s success probability is higher than that of before. During this plan, we skillfully selectively utilize two kinds of QNDS combined with the application of classical feedback operations. From this way we can greatly reduce the number of WNCK and QND detector. So we not only save resources and reduce decoherence phenomenon caused by scattering and absorption in the system.2. Implementation of quantum dense coding in the optical Kerr nonlinearity-cavity QND system.A) preparation of GHZ state:utilizing basic principle of coherent light field interacting with the WNCK and the aid of homodyne detection module applied on the probe mode, we control the interaction time to achieve three-particle state. This scheme can be extended to the preparation of N-particle GHZ state. Compare to the previous scheme, this scheme only uses linear optical elements and WNCKS. This scheme have characteristics such as, simple operation, high efficiency and more reasonable in the experiment and so on.B) Implementation of quantum dense coding.Suppose that Alice and Bob share the three-particle entangled state, Alice owns particles A and B, while Bob has particle C. Alice simultaneously performs each of the four local operations on her atoms to drive the system state locating on one of the eight states. Then Alice sends her atoms to Bob. To calculate what exactly operations Alice on her two particles, Bob applies three series of local operations on the three particles. Firstly, Bob operates X-quadrature homodyne measurement on coherence state associated with atoms A and C; Then, one Hadamard gate operation and one computation basis measurement are operated on atom A; The last operations are X-quadrature homodyne measurements on coherence state associated with atom B and atom C, and Hadamard gate operations on atom B and atom C. The dense coding has been successfully implemented up to now. By the end of this article we put the two-particle dense coding promotion to multi-particle dense coding, and analyze the influence of decoherence to this scheme at the end of the manuscript.