Quantum computers dream and realization

 

Rainer Blatt

 

Institute for Experimental Physics,

University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria

Rainer.Blatt@uibk.ac.at, http://heart-c704.uibk.ac.at

and

Institute for Quantum Optics and Quantum Information,

Austrian Academy of Sciences, Technikerstrasse 25, A-6020 Innsbruck, Austria

Rainer.Blatt@oeaw.ac.at, http://www.oeaw.ac.at/

 

 

Computational operations always rely on real physical processes, which are data input, data representation in a memory, data manipulation using algorithms and finally, the data output. With conventional computers all the processes are classical processes and can be described accordingly. Theoretically, it is known for several years now that certain computations could be processed much more efficiently using quantum mechanical operations. This requires the implementation of quantum bits (qubits), quantum registers and quantum gates and the development of quantum algorithms. Several approaches for the implementation of quantum computers will be presented, with special emphasis on the ion storage techniques. Experimental realizations of quantum registers and quantum gate operations using strings of trapped ions in a linear Paul trap will be discussed.

 

With a small ion-trap quantum computer based on two and three trapped Ca+ ions as qubits we have generated in a pre-programmed way specific quantum states. In particular, entangled states of two particles, i.e. Bell states, and of three particles, i.e. GHZ and W states, were generated using an algorithmic procedure. With a tomographic method, these states were subsequently analysed and the respective entanglement was characterized using various entanglement measures. W states with up to eight qubits were generated and prove that quantum registers can be built, prepared and controlled in a scalable way for an application with quantum computers. With Bell states as a resource, entangled states are applied for teleportation and, in metrology, for improved precision measurements.