5 research outputs found
Appearance of Topological Phases in Superconducting Nanocircuits
We construct non-Abelian geometric transformations in superconducting
nanocircuits, which resemble in properties the Aharonov-Bohm phase for an
electron transported around a magnetic flux line. The effective magnetic fields
can be strongly localized, and the path is traversed in the region where the
energy separation between the states involved is at maximum, so that the
adiabaticity condition is weakened. In particular, we present a scheme of
topological charge pumping.Comment: 4 pages, 4 figures, RevTeX4, References added, minor change
Quantum holonomies with Josephson-junction devices
We examined properties of a Josephson-junction system composed of two coupled
Cooper-pair boxes (charge qubits) as a candidate for observation of quantum
holonomies. We construct a universal set of transformations in a two-fold
degenerate ground state, and discuss the effects of noise in the system.Comment: RevTeX4, 5 pages, 3 figures, minor changes requested by Phys. Rev.
Geometry of an adiabatic passage at a level crossing
We discuss adiabatic quantum phenomena at a level crossing. Given a path in
the parameter space which passes through a degeneracy point, we find a
criterion which determines whether the adiabaticity condition can be satisfied.
For paths that can be traversed adiabatically we also derive a differential
equation which specifies the time dependence of the system parameters, for
which transitions between distinct energy levels can be neglected. We also
generalize the well-known geometric connections to the case of adiabatic paths
containing arbitrarily many level-crossing points and degenerate levels.Comment: 7 pages, 6 figures, RevTeX4, changes requested by Phys. Rev.
Stabilized parametric Cooper-pair pumping in a linear array of coupled Josephson junctions
We present an experimentally realizable stabilized charge pumping scheme in a
linear array of Cooper-pair boxes. The system design intrinsically protects the
pumping mechanism from severe errors, especially current reversal and
spontaneous charge excitation. The quantum Zeno effect is implemented to
further diminish pumping errors. The characteristics of this scheme are
considered from the perspective of improving the current standard. Such an
improvement bears relevence to the closure of the so-called measurement
triangle (see D. Averin [Nature 434, 285 (2005)]).Comment: Title changed, other corrections and modifications requested from
Phys. Rev. Let
Preparation and manipulation of a fault-tolerant superconducting qubit
We describe a qubit encoded in continuous quantum variables of an rf
superconducting quantum interference device. Since the number of accessible
states in the system is infinite, we may protect its two-dimensional subspace
from small errors introduced by the interaction with the environment and during
manipulations. We show how to prepare the fault-tolerant state and manipulate
the system. The discussed operations suffice to perform quantum computation on
the encoded state, syndrome extraction, and quantum error correction. We also
comment on the physical sources of errors and possible imperfections while
manipulating the system.Comment: Typo corrected, title changed as suggested by the editors of Phys.
Rev. B, references adde