Year: 2008
Type: dissertation
Abstract: There are numerous proposals for the physical realization of a quantum computer.However, distributed approaches, making use both of flying and stationary qubits, seem to constitute the most promising route towards a truly scalable device.Such systems guarantee extendibility, they incorporate the interface with communication applications and relax the physical realization of the device, allowing for defect tolerance.Flying qubits are included in the more general concept of a quantum bus, a mediating system which can be of higher dimension.Such a quantum bus can be used in the straightforward preparation of a standard multi-qubit resource enabling measurement based quantum computation, the cluster state.This constitutes the framework for the results presented in this thesis.We begin by investigating the effects of dissipation in the continuous variable bus scheme known as the qubus scheme.By considering loss in the bus as it mediates interactions between the stationary qubits, we obtain analytical results for the effective action of the induced quantum gate.We find that a particular two-qubit gate operates with high fidelity in the presence of moderate loss and give a simple iteration scheme to simplify the effects of loss on the qubits.We then attempt to reduce these effects by preparing the bus in more elaborate state, however no improvements are observed.We then apply the qubus scheme to the probabilistic generation of cluster states and develop an entangling gate working with high success probability.This allows us to produce cluster states far more efficiently than other proposals.Investigating new methods to analyze the performance of different generation strategies constitutes the second part of this set of results.We begin by making the large flow approximation, used in queuing theory, to obtain the optimal strategy in a regime with large resources.After what we take the other more familiar limit of single cluster growth and introduce absorbing Markov chains as a key mathematical tool.Finally we look at the transmission of composite quantum systems via a single higher dimensional bus.We provide generalized protocols and interactions guaranteeing a full transfer of the information from one composite system to another.These protocols can also serve information processing tasks, as useful logical operations can be applied to the data as it is transfered.We notice lastly that the qubus scheme constitutes a potential physical realization.
Author: Sebastien G. R. Louis
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W195059826