1,715 research outputs found
Conductance fluctuations in diffusive rings: Berry phase effects and criteria for adiabaticity
We study Berry phase effects on conductance properties of diffusive
mesoscopic conductors, which are caused by an electron spin moving through an
orientationally inhomogeneous magnetic field. Extending previous work, we start
with an exact, i.e. not assuming adiabaticity, calculation of the universal
conductance fluctuations in a diffusive ring within the weak localization
regime, based on a differential equation which we derive for the diffuson in
the presence of Zeeman coupling to a magnetic field texture. We calculate the
field strength required for adiabaticity and show that this strength is reduced
by the diffusive motion. We demonstrate that not only the phases but also the
amplitudes of the h/2e Aharonov-Bohm oscillations are strongly affected by the
Berry phase. In particular, we show that these amplitudes are completely
suppressed at certain magic tilt angles of the external fields, and thereby
provide a useful criterion for experimental searches. We also discuss Berry
phase-like effects resulting from spin-orbit interaction in diffusive
conductors and derive exact formulas for both magnetoconductance and
conductance fluctuations. We discuss the power spectra of the
magnetoconductance and the conductance fluctuations for inhomogeneous magnetic
fields and for spin-orbit interaction.Comment: 18 pages, 13 figures; minor revisions. To appear in Phys. Rev.
The sharp constant in the Hardy-Sobolev-Maz'ya inequality in the three dimensional upper half-space
It is shown that the sharp constant in the Hardy-Sobolev-Maz'ya inequality on
the three dimensional upper half space is given by the Sobolev constant. This
is achieved by a duality argument relating the problem to a
Hardy-Littlewood-Sobolev type inequality whose sharp constant is determined as
well.Comment: 9 page
Hyperfine-induced decoherence in triangular spin-cluster qubits
We investigate hyperfine-induced decoherence in a triangular spin-cluster for
different qubit encodings. Electrically controllable eigenstates of spin
chirality (C_z) show decoherence times that approach milliseconds, two orders
of magnitude longer than those estimated for the eigenstates of the total spin
projection (S_z) and of the partial spin sum (S_{12}). The robustness of
chirality is due to its decoupling from both the total- and individual-spin
components in the cluster. This results in a suppression of the effective
interaction between C_z and the nuclear spin bath
Quantum Computation and Spin Electronics
In this chapter we explore the connection between mesoscopic physics and
quantum computing. After giving a bibliography providing a general introduction
to the subject of quantum information processing, we review the various
approaches that are being considered for the experimental implementation of
quantum computing and quantum communication in atomic physics, quantum optics,
nuclear magnetic resonance, superconductivity, and, especially, normal-electron
solid state physics. We discuss five criteria for the realization of a quantum
computer and consider the implications that these criteria have for quantum
computation using the spin states of single-electron quantum dots. Finally, we
consider the transport of quantum information via the motion of individual
electrons in mesoscopic structures; specific transport and noise measurements
in coupled quantum dot geometries for detecting and characterizing
electron-state entanglement are analyzed.Comment: 28 pages RevTeX, 4 figures. To be published in "Quantum Mesoscopic
Phenomena and Mesoscopic Devices in Microelectronics," eds. I. O. Kulik and
R. Ellialtioglu (NATO Advanced Study Institute, Turkey, June 13-25, 1999
Berry phase and persistent current in disordered mesoscopic rings
A novel quantum interference effect in disordered quasi-one-dimensional rings
in the inhomogeneous magnetic field is reported. We calculate the canonical
disorder averaged persistent current using the diagrammatic perturbation
theory. It is shown that within the adiabatic regime the average current
oscillates as a function of the geometric flux which is related to the Berry
phase and the period becomes half the value of the case of a single
one-dimensional ring. We also discuss the magnetic dephasing effect on the
averaged current.Comment: 6 pages, RevTeX, 2 figures. To appear in Phys. Rev. B Rapid
Communications Vol.60 No.12 (1999
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