The Study Of Qubit Locigal Gates With Cross-Kerr Nonlinearity

As a new subject,quantum information science is the interdiscipline of traditional information processing science and quantum physics.The main tool for information processing is the computer.The traditional computer is not always meet the demand for computing power and speed.But the computer with quantum information technology can solve this problem.Compared with the traditional computer,the quantum computer's powerful computing power come from the quantum logical gates.Among the numerous quantum proposed for implementing quantum logical gates,photon systems are prominent candidates.Light as a carrier of information provides many advantages,such as boundless storing capacity,photons can ensure the security of information.Nonetheless there are also some downsides,such as difficult storage of photons and interactions between different photons.Those disadvantages make the schemes for implementing quantum logical gates with photon systems are still in the theoretical stage.We choose photon systems to realize the scheme for implementing quantum logical gates and solve the difficulty of interactions between different photons with cross-Kerr nonlinearities.In the second chapter of the article,we review the fundamentals of photonic quantum logic gates with linear optical elements and crossKerr nonlinearities,and give a detailed introduction to our two schemes about quantum logical gates.(1)The scheme for two-qubit logic gate:The phase shifts will be generated by the photons through the medium with weak cross-Kerr nonlinearity.Homodyne measurements be used to separate the coherent states.This method can improve the accuracy of judgment.(2)The scheme for three-qubit logic gate:we propose a scheme for three-qubit logic gate with same principle.We utilize quantum nondemolition detectors,so that the success probability of the gates is increased.there are fewer optical elements in our scheme,which brings great convenience to the practice of the scheme.Although our schemes are theoretical,they can be practiced with existing experimental conditions.The medium with cross-Kerr nonlinearities can solve the problem of photons' interactions.We use linearly polarizaed light as the signal modeand qubit is usually encoded on the vertical and horizintal polarization states.Our schemes have very important value for practicing quantum logic gates.