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
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