21,679 research outputs found
Efficient Schemes for Reducing Imperfect Collective Decoherences
We propose schemes that are efficient when each pair of qubits undergoes some
imperfect collective decoherence with different baths. In the proposed scheme,
each pair of qubits is first encoded in a decoherence-free subspace composed of
two qubits. Leakage out of the encoding space generated by the imperfection is
reduced by the quantum Zeno effect. Phase errors in the encoded bits generated
by the imperfection are reduced by concatenation of the decoherence-free
subspace with either a three-qubit quantum error correcting code that corrects
only phase errors or a two-qubit quantum error detecting code that detects only
phase errors, connected with the quantum Zeno effect again.Comment: no correction, 3 pages, RevTe
Negative Differential Resistance Induced by Mn Substitution at SrRuO3/Nb:SrTiO3 Schottky Interfaces
We observed a strong modulation in the current-voltage characteristics of
SrRuO/Nb:SrTiO Schottky junctions by Mn substitution in SrRuO,
which induces a metal-insulator transition in bulk. The temperature dependence
of the junction ideality factor indicates an increased spatial inhomogeneity of
the interface potential with substitution. Furthermore, negative differential
resistance was observed at low temperatures, indicating the formation of a
resonant state by Mn substitution. By spatially varying the position of the Mn
dopants across the interface with single unit cell control, we can isolate the
origin of this resonant state to the interface SrRuO layer. These results
demonstrate a conceptually different approach to controlling interface states
by utilizing the highly sensitive response of conducting perovskites to
impurities
Unified Analysis of Cosmological Perturbations in Generalized Gravity
In a class of generalized Einstein's gravity theories we derive the equations
and general asymptotic solutions describing the evolution of the perturbed
universe in unified forms. Our gravity theory considers general couplings
between the scalar field and the scalar curvature in the Lagrangian, thus
includes broad classes of generalized gravity theories resulting from recent
attempts for the unification. We analyze both the scalar-type mode and the
gravitational wave in analogous ways. For both modes the large scale evolutions
are characterized by the same conserved quantities which are valid in the
Einstein's gravity. This unified and simple treatment is possible due to our
proper choice of the gauges, or equivalently gauge invariant combinations.Comment: 4 pages, revtex, no figure
Single electron control in n-type semiconductor quantum dots using non-Abelian holonomies generated by spin orbit coupling
We propose that n-type semiconductor quantum dots with the Rashba and
Dresselhaus spin orbit interactions may be used for single electron
manipulation through adiabatic transformations between degenerate states. All
the energy levels are discrete in quantum dots and possess a double degeneracy
due to time reversal symmetryin the presence of the Rashba and/or Dresselhaus
spin orbit coupling terms. We find that the presence of double degeneracy does
not necessarily give rise to a finite non-Abelian (matrix) Berry phase. We show
that a distorted two-dimensional harmonic potential may give rise to
non-Abelian Berry phases. The presence of the non-Abelian Berry phase may be
tested experimentally by measuring the optical dipole transitions.Comment: accepted in Phys. Rev.
Coexistence of two- and three-dimensional Shubnikov-de Haas oscillations in Ar^+ -irradiated KTaO_3
We report the electron doping in the surface vicinity of KTaO_3 by inducing
oxygen-vacancies via Ar^+ -irradiation. The doped electrons have high mobility
(> 10^4 cm^2/Vs) at low temperatures, and exhibit Shubnikov-de Haas
oscillations with both two- and three-dimensional components. A disparity of
the extracted in-plane effective mass, compared to the bulk values, suggests
mixing of the orbital characters. Our observations demonstrate that Ar^+
-irradiation serves as a flexible tool to study low dimensional quantum
transport in 5d semiconducting oxides
Nanometer scale electronic reconstruction at the interface between LaVO3 and LaVO4
Electrons at interfaces, driven to minimize their free energy, are
distributed differently than in bulk. This can be dramatic at interfaces
involving heterovalent compounds. Here we profile an abrupt interface between V
3d2 LaVO3 and V 3d0 LaVO4 using electron energy loss spectroscopy. Although no
bulk phase of LaVOx with a V 3d1 configuration exists, we find a nanometer-wide
region of V 3d1 at the LaVO3/LaVO4 interface, rather than a mixture of V 3d0
and V 3d2. The two-dimensional sheet of 3d1 electrons is a prototypical
electronic reconstruction at an interface between competing ground states.Comment: 14 pages, 5 figure
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