TY - JOUR

T1 - Superconducting tetrahedral quantum bits

T2 - Emulation of a noise-resistant spin-1/2 system

AU - Feigel'man, M. V.

AU - Ioffe, L. B.

AU - Geshkenbein, V. B.

AU - Dayal, P.

AU - Blatter, G.

PY - 2004/12

Y1 - 2004/12

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=13844270873&partnerID=8YFLogxK

U2 - 10.1103/PhysRevB.70.224524

DO - 10.1103/PhysRevB.70.224524

M3 - Article

AN - SCOPUS:13844270873

VL - 70

SP - 224524-1-224524-16

JO - Physical Review B - Condensed Matter and Materials Physics

JF - Physical Review B - Condensed Matter and Materials Physics

SN - 1098-0121

IS - 22

M1 - 224524

ER -