Quantum Inf Process (2009) 8:51–54
Special issue on quantum computing with
Alexander N. Korotkov
Published online: 20 February 2009
© The Author(s) 2009. This article is published with open access at Springerlink.com
Ten years ago the ﬁrst superconducting qubit was demonstrated experimentally
. By now quantum computing with superconducting qubits has become a subject of
intensive experimental and theoretical research in dozens of groups around the world.
The idea of this Special Issue of the journal is to show the status of experimental
research in this area after the ﬁrst decade of work. Most of the best experimental
groups working with superconducting qubits (with a few regrettable exceptions) are
represented in this Special Issue. We hope that it gives a useful snapshot in time, dem-
onstrating the main experimental achievements and directions of research in super-
conducting quantum computing.
There are many possible physical realizations of qubits [2,3]. Among the candi-
date systems, the obvious advantages of quantum computing with Josephson junctions
are the efﬁcient control of a quantum circuit with voltage/current/microwave pulses
and use of a well-developed technology suitable for large scale integration. The fast
experimental progress in experiments with superconducting qubits in the last decade
conﬁrms the importance of these advantages.
Superconducting qubits come in a variety of types, which are often separated into
three categories: charge, ﬂux, and phase qubits (though not all groups use this termi-
nology). Single Cooper pair charge of an island carries the quantum information in the
charge qubit (e.g., [1,4–16]), while the superconducting phase is the relevant degree
of freedom for ﬂux and phase qubits, which differ by the logic state encoding: two
quantum levels in different wells of a potential proﬁle are used in the ﬂux qubit (e.g.,
[17–32]), and two levels in the same well are used in the phase qubit (e.g., [33–42]).
Guest Editor: Alexander N. Korotkov.
A. N. Korotkov (
Department of Electrical Engineering, University of California, Riverside, CA 92521, USA