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Superconducting tetrahedral quantum bits

M. V. Feigel'man·L. B. Ioffe·V. B. Geshkenbein·P. Dayal·G. Blatter
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Abstract

We propose a new design for a quantum bit with four superconducting islands in the topology of a symmetric tetrahedron, uniformly frustrated with one-half flux-quantum per loop and one-half Cooper-pair per island. This structure emulates a noise-resistant spin-1/2 system in a vanishing magnetic field. The tetrahedral quantum bit combines a number of advances such as a doubly degeneracy ground state minimizing decoherence via phonon radiation, a weak quadratic sensitivity to electric and magnetic noise, relieved constraints on the junction fabrication, a large freedom in manipulation, and attractive measurement schemes. The simultaneous appearance of a degenerate ground state and a weak noise sensitivity are consequences of the tetrahedral symmetry, while enhanced quantum fluctuations derive from the special magnetic frustration. We determine the spectral properties of the tetrahedral structure within a semiclassical analysis and confirm the results numerically. We show how proper tuning of the charge-frustration selects a doubly degenerate ground state and discuss the qubit's manipulation through capacitive and inductive coupling to external bias sources. The complete readout of all the spin-components is achieved through coupling of the internal qubit currents to external junctions driven close to criticality during the measurement.

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M. V. Feigel'man, L. B. Ioffe, V. B. Geshkenbein, P. Dayal, G. Blatter. 2004-07-26. Superconducting tetrahedral quantum bits. https://doi.org/10.1103/physrevlett.92.098301

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