Quantum Information Processing, Vol. 3, Nos. 1–5, October 2004 (© 2004)
Implementing Qubits with Superconducting
Michel H. Devoret
and John M. Martinis
Received March 2, 2004; accepted June 2, 2004
Superconducting qubits are solid state electrical circuits fabricated using tech-
niques borrowed from conventional integrated circuits. They are based on the
Josephson tunnel junction, the only non-dissipative, strongly non-linear circuit ele-
ment available at low temperature. In contrast to microscopic entities such as
spins or atoms, they tend to be well coupled to other circuits, which make them
appealling from the point of view of readout and gate implementation. Very
recently, new designs of superconducting qubits based on multi-junction circuits
have solved the problem of isolation from unwanted extrinsic electromagnetic per-
turbations. We discuss in this review how qubit decoherence is affected by the
intrinsic noise of the junction and what can be done to improve it.
KEY WORDS: Quantum information; quantum computation; superconducting
devices; Josephson tunnel junctions; integrated circuits.
PACS: 03.67.−a, 03.65.Yz, 85.25.−j, 85.35.Gv.
1.1. The Problem of Implementing a Quantum Computer
The theory of information has been revolutionized by the discovery
that quantum algorithms can run exponentially faster than their classical
counterparts, and by the invention of quantum error-correction proto-
These fundamental breakthroughs have lead scientists and engi-
neers to imagine building entirely novel types of information processors.
However, the construction of a computer exploiting quantum—rather than
Applied Physics Department, Yale University, New Haven, CT 06520, USA.
National Institute of Standards and Technology, Boulder, CO 80305, USA.
Present address: Physics Department, University of California, Santa Barbara, CA 93106,
To whom correspondence should be addressed. E-mail: email@example.com
1570-0755/04/1000-0163/0 © 2004 Springer Science+Business Media, Inc.