Abstract
Ever since Peter Shor's groundbreaking discovery in 1994
of an algorithm capable of factoring large integers on a
quantummechanical computer exponentially faster than
using any known classical method, research on quantum
computing has boomed. Quantum information  a unique
mixture of computer science, physics and mathematics 
has developed into a new branch of information theory. On
the experimental side, physicists from many different
disciplines including atomic, solidstate and
lowtemperature physics, as well as optics, are striving
today towards a practical quantum computer. All the
candidate quantum bit (qubit) technologies have one thing
in common: They rely on the controlled timeevolution of
a closed quantum system, a seemingly paradoxical task.
In this Thesis the temporal control of quantum systems is
studied. The topics included can be divided into two
according to the type of temporal evolution; geometrical
or dynamical. Geometrical realizationindependent methods
for quantum computing are studied first. Then the study
is extended into dynamical quantum computing and the
socalled Josephson chargequbit register is considered
as a test bench. Finally, a spinoff application of the
geometrical evolution of a Josephson junction system is
studied, i.e. Cooper pair pumping. A novel Cooper pair
pump, the Cooper pair "sluice", is introduced.
The work on quantum computing reported in this Thesis is
theoretical while the Cooper pair "sluice" is studied
both theoretically and experimentally. Numerical
simulations, both sequential and parallel, are used
extensively throughout the Thesis. The experiments were
carried out under cryogenic mK conditions and the sample
fabrication was done using ebeam nanolithography.
Because the execution time of a quantum algorithm is
always limited by the inevitable process of decoherence,
it is important to utilize any measure available for
accelerating quantum computations. It is found that
practical quantum algorithms could greatly benefit from
classical computeraided optimization. Moreover, it is
found that even a modest demonstrator of a full quantum
algorithm using Josephson charge qubits is just barely
realizable within presentday coherence times. However,
the experimental part of this Thesis shows clear evidence
of the functioning of the "sluice". While the worldwide
effort of improving the coherence properties of qubits is
underway, the "sluice" could well find practical use,
e.g., in metrology in the foreseeable future.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Award date  26 Nov 2004 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513864200 
Electronic ISBNs  9513864219 
Publication status  Published  2004 
MoE publication type  G5 Doctoral dissertation (article) 
Keywords
 quantum systems
 quantum mechanics
 quantum computing
 quantum algorithms
 Cooper pair pumping
 Josephson junction
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Niskanen, A. (2004). Control of Quantum Evolution and Josephson Junction Circuits: Dissertation. VTT Technical Research Centre of Finland. http://www.vtt.fi/inf/pdf/publications/2004/P552.pdf