MARC 主機 00000nam  2200337   4500 
001    AAI3190859 
005    20061201131708.5 
008    061201s2005                        eng d 
020    9780542343520 
035    (UnM)AAI3190859 
040    UnM|cUnM 
100 1  Robertson, Timothy Levi 
245 10 Fundamentals of flux-based quantum computing 
300    231 p 
500    Source: Dissertation Abstracts International, Volume: 66-
       10, Section: B, page: 5462 
500    Chair: John Clarke 
502    Thesis (Ph.D.)--University of California, Berkeley, 2005 
520    The study of Quantum Computing necessitates careful 
       examination of the most fundamental questions of Quantum 
       Theory, such as the measurement problem, and may lead to 
       important advances in practical applications such as 
       cryptography, search, and optimization. In order for a 
       Quantum Computer to be practically useful, the design must
       be scalable to hundreds of quantum bits, or qubits, while 
       maintaining quantum coherence. Qubits constructed from 
       superconducting electronics are promising because of their
       inherent scalability using established nano-fabrication 
       techniques. Superconducting qubits based on the flux 
       degree of freedom are insensitive to noise from charge 
       fluctuations and can be read-out using a Superconducting 
       Quantum Interference Device (SQUID). When properly 
       designed, a superconducting loop interrupted by three 
       Josephson junctions acts as a quantum two-state system 
520    In this Dissertation, an exact calculation of the energy 
       levels of the three junction flux qubit is used to design 
       samples consisting of one or two qubits to investigate 
       coherence properties. Careful attention is given to the 
       system electronics to minimize external sources of noise 
       acting back on the qubit that result in decoherence 
520    We report measurements on two superconducting flux qubits 
       coupled to a readout SQUID. Two on-chip flux bias lines 
       allow independent flux control of any two of the three 
       elements, as illustrated by a two-dimensional qubit flux 
       map. The application of microwaves yields a frequency-flux
       dispersion curve for 1- and 2-photon driving of the single
       -qubit excited state and reveals spurious resonances 
       intrinsic to each qubit. Coherent manipulation of the 
       single-qubit state results in Rabi oscillations, Ramsey 
       fringes, and Hahn spin-echos. This information is used to 
       develop a model of the decoherence caused by the 
       interaction of the qubit with its environment 
520    A detailed model for the interaction of a flux qubit with 
       a readout SQUID predicts the resolution of a measurement 
       and its effect on the qubit. Two adjustable inter-qubit 
       coupling systems that can produce bipolar coupling 
       strength are presented. These systems can be used to 
       produce the quantum Controlled-NOT gate, which when 
       combined with single qubit operations forms a basis for 
       Universal Quantum Computation 
590    School code: 0028 
590    DDC 
650  4 Physics, Condensed Matter 
690    0611 
710 20 University of California, Berkeley 
773 0  |tDissertation Abstracts International|g66-10B 
856 40 |u