Physical Society Colloquium

Towards a solid state quantum information processor:
manipulation and control of the quantum state of an electrical circuit

Michel Devoret

Yale University

Could the bits of a computer be atom-like entities behaving quantum-mechanically? The miniaturization of transistors and Boolean gates down to single atoms or electrons has been explored as early as the 1980's, but it is only in the last decade that the superiority, for certain class of problems, of the quantum computer over its conventional classical counterpart has been fully understood theoretically. This discovery has spurred a flurry of activity aimed at implementing practically a `quantum machine' which would compute. In our own laboratory, we have followed the lead of superconducting integrated circuits, whose fabrication directly benefits from a whole body of knowledge in micro- and nano-technology developed for semiconducting devices. The problem with solid-state implementations of `qubits' is their potentially strong coupling to unwanted degrees of freedom in the various materials of the circuit. Yet, we have shown experimentally that for a particular superconducting tunnel junction circuit - the so-called `quantronium' - electrical symmetries could be exploited to suppress, to a large extent, this undesirable coupling [1]. In the last few years, recent advances in Europe, Japan and the US have propelled the quantum mechanical coherence of superconducting circuits at a stage where genuine quantum information processing involving a register of several qubits can be engineered. We will discuss some of these possibilities.

[1] D. Vion et al., Science 296 (2002) 286