446 research outputs found
Manifestation of fundamental quantum complementarities in time-domain interference experiments with quantum dots: A theoretical analysis
A theoretical analysis is presented showing that fundamental complementarity
between the particle-like properties of an exciton confined in a semiconductor
quantum dot and the ability of the same system to show interference may be
studied in a time domain interference experiment, similar to those currently
performed. The feasibility of such an experiment, including required pulse
parameters and the dephasing effect of the environment, is studied.Comment: Final, considerably extended version; 8 pages, 3 figure
Decoherence of electron beams by electromagnetic field fluctuations
Electromagnetic field fluctuations are responsible for the destruction of
electron coherence (dephasing) in solids and in vacuum electron beam
interference. The vacuum fluctuations are modified by conductors and
dielectrics, as in the Casimir effect, and hence, bodies in the vicinity of the
beams can influence the beam coherence. We calculate the quenching of
interference of two beams moving in vacuum parallel to a thick plate with
permittivity . In case of an
ideal conductor or dielectric the dephasing is suppressed
when the beams are close to the surface of the plate, because the random
tangential electric field , responsible for dephasing, is zero at the
surface. The situation is changed dramatically when
or are finite. In this case there exists a layer near
the surface, where the fluctuations of are strong due to evanescent
near fields. The thickness of this near - field layer is of the order of the
wavelength in the dielectric or the skin depth in the conductor, corresponding
to a frequency which is the inverse electron time of flight from the emitter to
the detector. When the beams are within this layer their dephasing is enhanced
and for slow enough electrons can be even stronger than far from the surface
Theory of Neutron Diffraction from the Vortex Lattice in UPt3
Neutron scattering experiments have recently been performed in the
superconducting state of UPt3 to determine the structure of the vortex lattice.
The data show anomalous field dependence of the aspect ratio of the unit cell
in the B phase. There is apparently also a change in the effective coherence
length on the transition from the B to the C phases. Such observations are not
consistent with conventional superconductvity. A theory of these results is
constructed based on a picture of two-component superconductivity for UPt3. In
this way, these unusual observations can be understood. There is a possible
discrepancy between theory and experiment in the detailed field dependence of
the aspect ratio.Comment: 11 pages; uses REVTEX, APS and PRABIB styles; 2 Postscript figure
files include
Quantitative magneto-optical investigation of superconductor/ferromagnet hybrid structures
We present a detailed quantitative magneto-optical imaging study of several
superconductor/ferromagnet hybrid structures, including Nb deposited on top of
thermomagnetically patterned NdFeB, and permalloy/niobium with erasable and
tailored magnetic landscapes imprinted in the permalloy layer. The
magneto-optical imaging data is complemented with and compared to scanning Hall
probe microscopy measurements. Comprehensive protocols have been developed for
calibrating, testing, and converting Faraday rotation data to magnetic field
maps. Applied to the acquired data, they reveal the comparatively weaker
magnetic response of the superconductor from the background of larger fields
and field gradients generated by the magnetic layer.Comment: 21 pages, including 2 pages of supplementary materia
Concept of an ionizing time-domain matter-wave interferometer
We discuss the concept of an all-optical and ionizing matter-wave
interferometer in the time domain. The proposed setup aims at testing the wave
nature of highly massive clusters and molecules, and it will enable new
precision experiments with a broad class of atoms, using the same laser system.
The propagating particles are illuminated by three pulses of a standing
ultraviolet laser beam, which detaches an electron via efficient single
photon-absorption. Optical gratings may have periods as small as 80 nm, leading
to wide diffraction angles for cold atoms and to compact setups even for very
massive clusters. Accounting for the coherent and the incoherent parts of the
particle-light interaction, we show that the combined effect of phase and
amplitude modulation of the matter waves gives rise to a Talbot-Lau-like
interference effect with a characteristic dependence on the pulse delay time.Comment: 25 pages, 5 figure
Surface superconductivity and order parameter suppression in UPt
We show that a recent measurement of surface superconductivity in UPt
(Keller {\it et. al.}, Phys. Rev. Lett. {\bf 73}, 2364 (1994)) can be
understood if the superconducting pair wavefunction is suppressed
anisotropically at a vacuum to superconductor interface. Further measurements
of surface superconductivity can distinguish between the various
phenomenological models of superconducting UPt.Comment: 4 pages, latex, 2 Figures available upon request
([email protected]
Effect of diffusive boundaries on surface superconductivity in unconventional superconductors
Boundary conditions for a superconducting order parameter at a diffusive
scattering boundary are derived from microscopic theory. The results indicate
that for all but isotropic gap functions the diffusive boundary almost
completely suppresses surface superconductivity in the Ginzburg-Landau regime.
This indicates that in anisotropic superconductors surface superconductivity
can only be observed for surface normals along high symmetry directions where
atomically clean surfaces can be cleaved.Comment: Latex File, 12 pages, 2 Postscript figures, to appear in Phys. Rev. B
(June 1 1996
Channel Interference in a Quasi Ballistic Aharonov-Bohm Experiment
New experiments are presented on the transmission of electron waves through a
2DEG (2 dimensional electron gas) ring with a gate on top of one of the
branches. Magnetoconductance oscillations are observed, and the phase of the
Aharanov-Bohm signal alternates between 0 and pi as the gate voltage is
scanned. A Fourier transform of the data reveals a dominant period in the
voltage which corresponds to the energy spacing between successive transverse
modes.A theoretical model including random phase shifts between successive
modes reproduces the essential features of the experiment.Comment: 4 pages, 6 Postscript figures, TEX, submitted to Physical Review
Letter
Self-aligned nanoscale SQUID on a tip
A nanometer-sized superconducting quantum interference device (nanoSQUID) is
fabricated on the apex of a sharp quartz tip and integrated into a scanning
SQUID microscope. A simple self-aligned fabrication method results in
nanoSQUIDs with diameters down to 100 nm with no lithographic processing. An
aluminum nanoSQUID with an effective area of 0.034 m displays flux
sensitivity of 1.8 \mu_B/\mathrm{Hz}^{1/2}$ and high bandwidth, the SQUID on a tip is a highly
promising probe for nanoscale magnetic imaging and spectroscopy.Comment: 14 manuscript pages, 5 figure
Nonlocality, Bell's Ansatz and Probability
Quantum Mechanics lacks an intuitive interpretation, which is the cause of a
generally formalistic approach to its use. This in turn has led to a certain
insensitivity to the actual meaning of many words used in its description and
interpretation. Herein, we analyze carefully the possible mathematical meanings
of those terms used in analysis of EPR's contention, that Quantum Mechanics is
incomplete, as well as Bell's work descendant therefrom. As a result, many
inconsistencies and errors in contemporary discussions of nonlocality, as well
as in Bell's Ansatz with respect to the laws of probability, are identified.
Evading these errors precludes serious conflicts between Quantum Mechanics and
both Special Relativity and Philosophy.Comment: 8&1/2 pages revtex; v2: many corrections, clairifications &
extentions, all small; v3: editorial scru
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