Superconducting tetrahedral quantum bits: Emulation of a noise-resistant spin-1/2 system

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

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We propose a 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 degenerate 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 the spin components σi i=x,y,z, is achieved through coupling of the internal qubit currents to external junctions driven close to criticality during the measurement.

Original languageEnglish (US)
Article number224524
Pages (from-to)224524-1-224524-16
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number22
StatePublished - Dec 2004

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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