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Introduction: Oligocene to Pleistocene Eustatic Change at the New Jersey Continental Margin--a Test of Sequence Stratigraphy
The emergence of seismic/sequence stratigraphy since the late 1970s has led to a revolution in stratigraphy and a renewal of interest in the stratigraphic response to eustasy. Two arguments were advanced in support of the eustatic interpretation. One involved widespread seismic evidence for the existence of regional unconformities (sequence boundaries) characterized by apparently abrupt basinward shifts in onlap, which were interpreted to imply relatively rapid falls of sea level with amplitudes of up to several hundred meters. The second was based on the purported global synchroneity of these unconformities, which, if correct, would be difficult to explain by other than a eustatic mechanism. The primary goals of Leg 174A are the following: 1. To date as precisely as possible sequence boundaries of Oligocene—Pleistocene age, and to compare this stratigraphic record with the timing of glacial-eustatic changes inferred from deep-sea d18O variations; 2. To place constraints on the amplitudes and rates of sea-level change that may have been responsible for unconformity development; 3. To assess the relationships between depositional facies and sequence architecture; and 4. To provide a baseline for future scientific ocean drilling that will address the effects and timing of sea-level changes on this and other passive continental margins. An additional goal for Leg 174A is technical. The leg represents the first attempt by scientific ocean drilling in almost 30 years to sample a thickly sedimented continental margin in water depths less than 150 m. Two sites (Sites 1071 and 1072) are located on the outer part of the continental shelf in water depths of 88-90 and 98-100 m, respectively. An additional site (Site 1073) is located on the uppermost continental slope, part of the Hudson Apron, in a water depth of 639 m
Nuclear spin relaxation probed by a single quantum dot
We present measurements on nuclear spin relaxation probed by a single quantum
dot in a high-mobility electron gas. Current passing through the dot leads to a
spin transfer from the electronic to the nuclear spin system. Applying electron
spin resonance the transfer mechanism can directly be tuned. Additionally, the
dependence of nuclear spin relaxation on the dot gate voltage is observed. We
find electron-nuclear relaxation times of the order of 10 minutes
Molecular states in carbon nanotube double quantum dots
We report electrical transport measurements through a semiconducting
single-walled carbon nanotube (SWNT) with three additional top-gates. At low
temperatures the system acts as a double quantum dot with large inter-dot
tunnel coupling allowing for the observation of tunnel-coupled molecular states
extending over the whole double-dot system. We precisely extract the tunnel
coupling and identify the molecular states by the sequential-tunneling line
shape of the resonances in differential conductance.Comment: 5 pages, 4 figure
Single-electron quantum dot in Si/SiGe with integrated charge-sensing
Single-electron occupation is an essential component to measurement and
manipulation of spin in quantum dots, capabilities that are important for
quantum information processing. Si/SiGe is of interest for semiconductor spin
qubits, but single-electron quantum dots have not yet been achieved in this
system. We report the fabrication and measurement of a top-gated quantum dot
occupied by a single electron in a Si/SiGe heterostructure. Transport through
the quantum dot is directly correlated with charge-sensing from an integrated
quantum point contact, and this charge-sensing is used to confirm
single-electron occupancy in the quantum dot.Comment: 3 pages, 3 figures, accepted version, to appear in Applied Physics
Letter
Charge Sensing of an Artificial H2+ Molecule
We report charge detection studies of a lateral double quantum dot with
controllable charge states and tunable tunnel coupling. Using an integrated
electrometer, we characterize the equilibrium state of a single electron
trapped in the doubled-dot (artificial H2+ molecule) by measuring the average
occupation of one dot. We present a model where the electrostatic coupling
between the molecule and the sensor is taken into account explicitly. From the
measurements, we extract the temperature of the isolated electron and the
tunnel coupling energy. It is found that this coupling can be tuned between 0
and 60 micro electron-volt in our device.Comment: 5 pages, 4 figures. Revised version with added material. To be
published in Physical Review
Control of Dephasing and Phonon Emission in Coupled Quantum Dots
We predict that phonon subband quantization can be detected in the non-linear
electron current through double quantum dot qubits embedded into nano-size
semiconductor slabs, acting as phonon cavities. For particular values of the
dot level splitting , piezo-electric or deformation potential
scattering is either drastically reduced as compared to the bulk case, or
strongly enhanced due to phonon van Hove singularities. By tuning via
gate voltages, one can either control dephasing, or strongly increase emission
into phonon modes with characteristic angular distributions.Comment: 4 pages, 3 figures, accepted for publication as Rapid Comm. in Phys.
Rev.
Dicke Effect in the Tunnel Current through two Double Quantum Dots
We calculate the stationary current through two double quantum dots which are
interacting via a common phonon environment. Numerical and analytical solutions
of a master equation in the stationary limit show that the current can be
increased as well as decreased due to a dissipation mediated interaction. This
effect is closely related to collective, spontaneous emission of phonons (Dicke
super- and subradiance effect), and the generation of a `cross-coherence' with
entanglement of charges in singlet or triplet states between the dots.
Furthermore, we discuss an inelastic `current switch' mechanism by which one
double dot controls the current of the other.Comment: 12 pages, 6 figures, to appear in Phys. Rev.
Photon-Assisted Transport Through Ultrasmall Quantum Dots: Influence of Intradot Transitions
We study transport through one or two ultrasmall quantum dots with discrete
energy levels to which a time-dependent field is applied (e.g., microwaves).
The AC field causes photon-assisted tunneling and also transitions between
discrete energy levels of the dot. We treat the problem by introducing a
generalization of the rotating-wave approximation to arbitrarily many levels.
We calculate the dc-current through one dot and find satisfactory agreement
with recent experiments by Oosterkamp et al. . In addition, we propose a novel
electron pump consisting of two serially coupled single-level quantum dots with
a time-dependent interdot barrier.Comment: 16 pages, Revtex, 10 eps-figure
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