12,132 research outputs found
Tunable effective g-factor in InAs nanowire quantum dots
We report tunneling spectroscopy measurements of the Zeeman spin splitting in
InAs few-electron quantum dots. The dots are formed between two InP barriers in
InAs nanowires with a wurtzite crystal structure grown by chemical beam
epitaxy. The values of the electron g-factors of the first few electrons
entering the dot are found to strongly depend on dot size and range from close
to the InAs bulk value in large dots |g^*|=13 down to |g^*|=2.3 for the
smallest dots. These findings are discussed in view of a simple model.Comment: 4 pages, 3 figure
Parity independence of the zero-bias conductance peak in a nanowire based topological superconductor-quantum dot hybrid device
We explore the signatures of Majorana fermions in a nanowire based
topological superconductor-quantum dot-topological superconductor hybrid device
by charge transport measurements. The device is made from an epitaxially grown
InSb nanowire with two superconductor Nb contacts on a Si/SiO substrate. At
low temperatures, a quantum dot is formed in the segment of the InSb nanowire
between the two Nb contacts and the two Nb contacted segments of the InSb
nanowire show superconductivity due to the proximity effect. At zero magnetic
field, well defined Coulomb diamonds and the Kondo effect are observed in the
charge stability diagram measurements in the Coulomb blockade regime of the
quantum dot. Under the application of a finite, sufficiently strong magnetic
field, a zero-bias conductance peak structure is observed in the same Coulomb
blockade regime. It is found that the zero-bias conductance peak is present in
many consecutive Coulomb diamonds, irrespective of the even-odd parity of the
quasi-particle occupation number in the quantum dot. In addition, we find that
the zero-bias conductance peak is in most cases accompanied by two differential
conductance peaks, forming a triple-peak structure, and the separation between
the two side peaks in bias voltage shows oscillations closely correlated to the
background Coulomb conductance oscillations of the device. The observed
zero-bias conductance peak and the associated triple-peak structure are in line
with the signatures of Majorana fermion physics in a nanowire based topological
superconductor-quantum dot-topological superconductor system, in which the two
Majorana bound states adjacent to the quantum dot are hybridized into a pair of
quasi-particle states with finite energies and the other two Majorana bound
states remain as the zero-energy modes located at the two ends of the entire
InSb nanowire.Comment: 6 pages, 4 figure
Minimum detection efficiency for a loophole-free atom-photon Bell experiment
In Bell experiments, one problem is to achieve high enough photodetection to
ensure that there is no possibility of describing the results via a local
hidden-variable model. Using the Clauser-Horne inequality and a two-photon
non-maximally entangled state, a photodetection efficiency higher than 0.67 is
necessary. Here we discuss atom-photon Bell experiments. We show that, assuming
perfect detection efficiency of the atom, it is possible to perform a
loophole-free atom-photon Bell experiment whenever the photodetection
efficiency exceeds 0.50.Comment: REVTeX4, 4 pages, 1 figur
Correlation-induced conductance suppression at level degeneracy in a quantum dot
The large, level-dependent g-factors in an InSb nanowire quantum dot allow
for the occurrence of a variety of level crossings in the dot. While we observe
the standard conductance enhancement in the Coulomb blockade region for aligned
levels with different spins due to the Kondo effect, a vanishing of the
conductance is found at the alignment of levels with equal spins. This
conductance suppression appears as a canyon cutting through the web of direct
tunneling lines and an enclosed Coulomb blockade region. In the center of the
Coulomb blockade region, we observe the predicted correlation-induced
resonance, which now turns out to be part of a larger scenario. Our findings
are supported by numerical and analytical calculations.Comment: 5 pages, 4 figure
A Fast Sextupole Probe for Snapback Measurement in the LHC Dipoles
In superconducting particle accelerators a fast change of the magnetic field occurs during the first few seconds after the start of an energy ramp. Standard magnetic measurements using a coil rotating at 1 Hz do not have the time resolution required to completely resolve this phase, usually called snapback. For this reason we have developed a new and fast system dedicated to sextupole measurements. The basic component consists of three Hall plates mounted on a ring. In an ideal case this arrangement compensates the main dipole field and produces a signal proportional to the sextupole only. Mechanical tolerances and differences in the sensitivity of the Hall plates are compensated by instrumentation amplifiers and an in situ fine adjustment of the probe orientation. Using this hybrid compensation technique we have measured sextupole variations in an LHC dipole prototype during snapback at a rate of 5 Hz. In this paper we present details on the device and the results of our measurements
The Electrostatic Ion Beam Trap : a mass spectrometer of infinite mass range
We study the ions dynamics inside an Electrostatic Ion Beam Trap (EIBT) and
show that the stability of the trapping is ruled by a Hill's equation. This
unexpectedly demonstrates that an EIBT, in the reference frame of the ions
works very similar to a quadrupole trap. The parallelism between these two
kinds of traps is illustrated by comparing experimental and theoretical
stability diagrams of the EIBT. The main difference with quadrupole traps is
that the stability depends only on the ratio of the acceleration and trapping
electrostatic potentials, not on the mass nor the charge of the ions. All kinds
of ions can be trapped simultaneously and since parametric resonances are
proportional to the square root of the charge/mass ratio the EIBT can be used
as a mass spectrometer of infinite mass range
Comparing Star Formation on Large Scales in the c2d Legacy Clouds: Bolocam 1.1 mm Dust Continuum Surveys of Serpens, Perseus, and Ophiuchus
We have undertaken an unprecedentedly large 1.1 millimeter continuum survey
of three nearby star forming clouds using Bolocam at the Caltech Submillimeter
Observatory. We mapped the largest areas in each cloud at millimeter or
submillimeter wavelengths to date: 7.5 sq. deg in Perseus (Paper I), 10.8 sq.
deg in Ophiuchus (Paper II), and 1.5 sq. deg in Serpens with a resolution of
31", detecting 122, 44, and 35 cores, respectively. Here we report on results
of the Serpens survey and compare the three clouds. Average measured angular
core sizes and their dependence on resolution suggest that many of the observed
sources are consistent with power-law density profiles. Tests of the effects of
cloud distance reveal that linear resolution strongly affects measured source
sizes and densities, but not the shape of the mass distribution. Core mass
distribution slopes in Perseus and Ophiuchus (alpha=2.1+/-0.1 and
alpha=2.1+/-0.3) are consistent with recent measurements of the stellar IMF,
whereas the Serpens distribution is flatter (alpha=1.6+/-0.2). We also compare
the relative mass distribution shapes to predictions from turbulent
fragmentation simulations. Dense cores constitute less than 10% of the total
cloud mass in all three clouds, consistent with other measurements of low
star-formation efficiencies. Furthermore, most cores are found at high column
densities; more than 75% of 1.1 mm cores are associated with Av>8 mag in
Perseus, 15 mag in Serpens, and 20-23 mag in Ophiuchus.Comment: 32 pages, including 18 figures, accepted for publication in Ap
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