Abstract
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) 
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Keywords
 quantum systems
 quantum mechanics
 quantum computing
 quantum algorithms
 Cooper pair pumping
 Josephson junction
Cite this
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Control of Quantum Evolution and Josephson Junction Circuits : Dissertation. / Niskanen, Antti.
Espoo : VTT Technical Research Centre of Finland, 2004. 111 p.Research output: Thesis › Dissertation › Collection of Articles
TY  THES
T1  Control of Quantum Evolution and Josephson Junction Circuits
T2  Dissertation
AU  Niskanen, Antti
PY  2004
Y1  2004
N2  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.
AB  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.
KW  quantum systems
KW  quantum mechanics
KW  quantum computing
KW  quantum algorithms
KW  Cooper pair pumping
KW  Josephson junction
M3  Dissertation
SN  9513864200
T3  VTT Publications
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 