  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.
