Fluxonium: Single Cooper-Pair Circuit Free of Charge Offsets

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Science  02 Oct 2009:
Vol. 326, Issue 5949, pp. 113-116
DOI: 10.1126/science.1175552

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Quiet, Please

One approach for building quantum computers is based on superconductors with appropriately designed components to control the pairs of charges flowing through the circuits. However, at the single-electron level, required quantum noise—generated by quantum fluctuations and throwing offset charges into the device—presents a real problem in manipulating the delicate quantum states of the qubits. Manucharyan et al. (p. 113) present a clever piece of quantum circuit engineering that can suppress the effect of the quantum noise and allow the quantum circuit to operate without disturbance.


The promise of single Cooper-pair quantum circuits based on tunnel junctions for metrology and quantum information applications is severely limited by the influence of offset charges: random, slowly drifting microscopic charges inherent in many solid-state systems. By shunting a small junction with the Josephson kinetic inductance of a series array of large-capacitance tunnel junctions, thereby ensuring that all superconducting islands are connected to the circuit by at least one large junction, we have realized a new superconducting artificial atom that is totally insensitive to offset charges. Yet its energy levels manifest the anharmonic structure associated with single Cooper-pair effects, a useful component for solid-state quantum computation.

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