119 research outputs found
Influence of Nuclear Spin Polarization on Quantum Wire Conductance
In this work, we study a possibility to measure the transverse and
longitudinal relaxation times of a collection of polarized nuclear spins
located in the region of a quantum wire via its conductance. The interplay of
an external in-plane magnetic field, spin-orbit interaction, and the changing
field of the spin-polarized nuclei cause the conductance of the quantum wire to
evolve in time. We show that it is possible to extract the transverse and
longitudinal relaxation times of the spin-polarized nuclei from the time
dependence of the conductance.Comment: Presented at the 2004 IEEE NTC Quantum Device Technology Worksho
Decoherence in adiabatic quantum computation
We have studied the decoherence properties of adiabatic quantum computation
(AQC) in the presence of in general non-Markovian, e.g., low-frequency, noise.
The developed description of the incoherent Landau-Zener transitions shows that
the global AQC maintains its properties even for decoherence larger than the
minimum gap at the anticrossing of the two lowest energy levels. The more
efficient local AQC, however, does not improve scaling of the computation time
with the number of qubits as in the decoherence-free case. The scaling
improvement requires phase coherence throughout the computation, limiting the
computation time and the problem size n.Comment: 4 pages, 2 figures, published versio
Solar Collection of Evacuated Tubes in a Residential Electrical Power System
Honda I-Dream Mobility Award for innovationThis report investigates the solar thermal collection process to be utilized in a residential Rankine Cycle power plant. The projected rise in fossil fuel prices due to increased emission standards, fossil fuel depletion, and increasing demand gives motivation for designing a new residential solar thermal power plant. Since utility scale solar thermal is the most cost effective method of solar power production, this report seeks to scale the technology down to a residential level. Between parabolic troughs, flat plat solar collectors, and evacuated tubes, the most optimal solar collection tool for residential applications is evacuated tubes. With Isobutane as a working fluid, this report will theoretically show that under sunny conditions a residential system can be designed to produce 10 kWh of electricity. Verification tests will be carried out to give evidence that the solar collection design can indeed deliver enough energy for 10 kWh to be produced. Initial tests show positive results even though the target temperature of 90 ËšC was not reached. The verification tests do not confirm the solar collection system entirely, but gives a positive outlook for future tests and development in the residential solar power plant.No embarg
Polarization of Nuclear Spins from the Conductance of Quantum Wires
We devise an approach to measure the polarization of nuclear spins via conductance measurements. Specifically, we study the combined effect of external magnetic field, nuclear spin polarization, and Rashba spin-orbit interaction on the conductance of a quantum wire. Nonequilibrium nuclear spin polarization affects the electron energy spectrum making it time dependent. Changes in the extremal points of the spectrum result in time dependence of the conductance. The conductance oscillation pattern can be used to obtain information about the amplitude of the nuclear spin polarization and extract the characteristic time scales of the nuclear spin subsystem
Effect of Spin-Orbit Interaction and In-Plane Magnetic Field on the Conductance of a Quasi-One-Dimensional System
We study the effect of spin-orbit interaction and in-plane effective magnetic field on the conductance of a quasi-one-dimensional ballistic electron system. The effective magnetic field includes the externally applied field, as well as the field due to polarized nuclear spins. The interplay of the spin-orbit interaction with effective magnetic field significantly modifies the band structure, producing additional subband extrema and energy gaps, introducing the dependence of the subband energies on the field direction. We generalize the Landauer formula at finite temperatures to incorporate these special features of the dispersion relation. The obtained formula describes the conductance of a ballistic conductor with an arbitrary dispersion relation
Tunneling without tunneling: wavefunction reduction in a mesoscopic qubit
The transformation cycle and associated inequality are suggested for the
basic demonstration of the wavefunction reduction in a mesoscopic qubit in
measurements with quantum-limited detectors. Violation of the inequality would
show directly that the qubit state changes in a way dictated by the
probabilistic nature of the wavefunction and inconsistent with the dynamics of
the Schr\"{o}dinger equation: the qubit tunnels through an infinitely large
barrier. Estimates show that the transformation cycle is within the reach of
current experiments with superconducting qubits.Comment: 5 pages, 2 figure
Correlated transport of FQHE quasiparticles in a double-antidot system
We have calculated the linear conductance associated with tunneling of
individual quasiparticles of primary quantum Hall liquids with filling factors
through a system of two antidots in series. On-site Coulomb
interaction simulates the Fermi exclusion and makes the quasiparticle dynamics
similar to that of tunneling electrons. The liquid edges serve as the
quasiparticle reservoirs, and also create the dissipation mechanism for
tunneling between the antidots. In the regime of strong dissipation, the
conductance should exhibit resonant peaks of unusual form and a width
proportional to the quasiparticle interaction energy . In the weakly-damped
regime, the shape of the resonant conductance peaks reflects coherent tunnel
coupling of the antidots. The Luttinger-liquid singularity in the rates of
quasiparticle tunneling to/from the liquid edges manifests itself as an
additional weak resonant structure in the conductance curves.Comment: 9 pages including 5 figure
Effect of Spin-Orbit Interaction and In-Plane Magnetic Field on the Conductance of a Quasi-One-Dimensional System
We study the effect of spin-orbit interaction and in-plane effective magnetic
field on the conductance of a quasi-one-dimensional ballistic electron system.
The effective magnetic field includes the externally applied field, as well as
the field due to polarized nuclear spins. The interplay of the spin-orbit
interaction with effective magnetic field significantly modifies the band
structure, producing additional sub-band extrema and energy gaps, introducing
the dependence of the sub-band energies on the field direction. We generalize
the Landauer formula at finite temperatures to incorporate these special
features of the dispersion relation. The obtained formula describes the
conductance of a ballistic conductor with an arbitrary dispersion relation.Comment: will appear in Physical Review
Low temperature, authigenic illite and carbonates in a mixed dolomite-clastic lagoonal and pedogenic setting, Spanish Central System, Spain
The aim of this study was to further our understanding of the pedogenic and lacustrine modification of clay minerals. Some of these modifications are of special interest because they constitute reverse weathering reactions, rare in surface environments, and because there is not yet an accurate assessment of their global relevance in mineralogical and geochemical cycles. For this study, two sections from the Central System in Spain were selected. Both are sections through the Uppper Cenomanian-Turonian mixed clastic and carbonate succession, containing both calcite and dolomite, in the Sierra de Guadarrama. Mid-Turonian sea level fall resulted in the formation of a coastal plain environment in which extensive pedogenesis occurred around saline lagoons. The mineralogical changes that have occurred as a result of sedimentation in saline lagoons and as a consequence of pedogenesis are described. Textural relationships indicate that the dolomite cement pre-dates the calcite. Silicate minerals are represented by quartz, kaolinite, illite-smectite, illite, minor plagioclase and alkali feldspar, and trace chlorite and palygorskite. There is a positive correlation between the intensity of pedogenesis and the proportion of illite in the clay assemblage in one of the sections, indicating pedogenic illitisation. In this section, the intensity of the illitisation process increases up, reaching a maximum where pedogenesis is most intense in the middle part, and then decreases as marine influence increases towards the top of the Alcorlo Formation and the overlying marine Tranquera Formation. The clay assemblages are consistent with a slow transformation process from 42 kaolinite to illite by way of illite-smectite, taking place under surface conditions. The illitisation process has resulted in a less Fe-rich, more Mg-, and Al-rich illite than the majority of previously documented cases in the near surface. Formation of Al-rich illite is not therefore restricted to the deep subsurface.
The mechanism for low temperature illitisation involves enhanced layer charge resulting from Mg2+ substitution for Al3+ (or Fe3+) and Fe3+ to Fe2+ reduction. Mg2+ enrichment may have occurred principally in saline lagoons or lakes, while Fe3+ to Fe2+ reduction occurred as a result of wetting and drying in a pedogenic environment. So far as it has been possible to establish, this dual mechanism has not previously been documented. This study indicates clearly that the dolomite and calcite are authigenic cements that precipitated in a clastic sediment, probably soon after deposition. Dolomitisation and Mg enrichment of the clay may have occurred at the same time. Seawater is the most probable source of Mg
- …