Coherent control of macroscopic quantum states in a single-Cooper-pair box

Article

关键词: SMALL JOSEPHSON-JUNCTIONS;    SPECTROSCOPY;    COMPUTATION;    CIRCUITS;    DOT;   

DOI  :  10.1038/19718

来源: SCIE

【 摘 要 】

A nanometre-scale superconducting electrode connected to a reservoir via a Josephson junction constitutes an artificial two-level electronic system: a single-Cooper-pair box. The two levels consist of charge states (differing by 2e, where e is the electronic charge) that are coupled by tunnelling of Cooper pairs through the junction. Although the two-level system is macroscopic, containing a large number of electrons, the two charge states can be coherently superposed(1-4). The Cooper-pair box has therefore been suggested(5-7) as a candidate for a quantum bit or 'qubit'-the basic component of a quantum computer. Here we report the observation of quantum oscillations in a single-Cooper-pair box. By applying a short voltage pulse via a gate electrode, we can control the coherent quantum state evolution: the pulse modifies the energies of the two charge states nonadiabatically, bringing them into resonance. The resulting state-a superposition of the two charge states-is detected by a tunnelling current through a probe junction. Our results demonstrate electrical coherent control of a qubit in a solid-state electronic device.

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