Quantum Information Processing In The Trapped Ion Systems

The quantum information science is the combination of quantum mechanics and theinformation theory, which is formalized in the 1980s, and it can solve many informationprocessing problems which cannot be achieved with the classical information theory. Itis rapidly growing brand-new cross science subject with a wide and profound future ap-plication field since then. In the field of quantum information, trapped ion systems isconsidered to be one of the most prospective physical systems to realize quantum infor-mation processing and quantum computer.With the development of laser cooling and the related experimental techniques, thestudy and the application for the trapped ionic system have developed greatly, and makeit as a important task in the quantum information processing. The thesis consists of fivechapters.In chapter 1, some basic theories of trapped ionic system are introduced, includingthe history background and the presentation of study, then the basic theories of quantuminformation are explicated. It forms the theoretical basic of the works in the followingchapters.In chapter 2, beyond the Lamb-Dicke limit, we investigate the squeezing propertiesof the trapped ion in the travelling-wave laser. It is shown that squeezing properties ofthe trapped ion in the travelling-wave laser are strongly affected by the sideband numberk, the Lamb-Dicke parameterηand the initial average phonon number.In chapter 3, an effective scheme for the entanglement concentration of four-particlestate via entanglement swapping is proposed in an ion trap. Taking the maximally entan-gled state after concentration as a quantum channel, we can faithfully and determinativelyteleport quantum entangled states without the joint Bell-state measurement. In the pro- cess of constructing the quantum channel, we adopt entanglement swapping to avoid thedecrease of entanglement during the distribution of particles, and it is insensitive to theheating coming from a vibrational mode. Thus our scheme provides a new prospect forquantum teleportation over a longer distance.In chapter 4, we introduce some basic theories of quantum dense coding, the realiza-tion of the quantum dense coding can be implemented with ions confined in a linear trapand interacting with laser beams is investigated. The scheme is insensitive to the interac-tion between the quantum channel and the environment. The Bell-state measurement isnot involved and the probability of success in our scheme is 1.0.In chapter 5, a summary of the work and an outlook of this aspect are given.