Nuclear Magnetic Resonance Implementation Of Two Precision Quantum Measurement Algorithm

Quantum information science(QIS) is a new convergence of two of quantummechanics and information science. QIS, which can provide new principles andtechniques for information science, includes quantum information and quantumcomputation etc. Quantum information processing (QIP) can, in theory, break restrictionsof classical information processing; its great scientific significance has more and moreattracted interest from physicists and information scientists, so, at present, it is one of thefrontiers of physics and the hot topics of science. Operations of quantum gates andsimple quantum algorithms have been demonstrated experimentally. But it is difficult toconstruct scalable quantum computers, that is, the extension to multi-qubit quantumcomputers. The experiments have shown that nuclear magnetic resonance(NMR)quantum computing is one of the fastest development fields and the most realistic meansin QIS. Therefore, on the basis of experimental techniques of NMR quantum computing,experimental demonstrations of two quantum algorithms on precision measurements arechosen as the subject of my dissertation. The main results of the dissertation are asfollows:1,Quantum phase estimation algorithm (PEA) with 20 bits of the binary expansionis, for the first time, demonstrated by using feedback on 2-qubit NMR computers. Errorsof experimantal results are in agreement with theoretical ones. It provides a typicalexample for feedback quantum PEA, and can open up a new way to implement quantumprecision measurements on muti-qubit quantum computers with only few qubits.2,Controlling quantum states with "shadow pair pulses" can identify peaks ofspectra which can not be resolved by usual techniques of optical spectroscopy, and itprovides an excellent experimental methods for precision measurements of the peaks ofspectra. It can be used to realize exact coherent control of quantum states on NMR orother systems. In a word, our investigations provide a principle experiment for demonstrating theQIP of multi-qubit quantum algorithms on quantum computers with few qubits. With thedevelopment of principles and techniques, QIP can play an important role in multi-qubitprecision measurements and control.