1,774 research outputs found
Measurement of the current-phase relation of superconducting atomic contacts
We have probed the current-phase relation of an atomic contact placed with a
tunnel junction in a small superconducting loop. The measurements are in
quantitative agreement with the predictions of a resistively shunted SQUID
model in which the Josephson coupling of the contact is calculated using the
independently determined transmissions of its conduction channels.Comment: to be published in Physical Review Letter
Evidence of Klein tunneling in graphene p-n junctions
Transport through potential barriers in graphene is investigated using a set
of metallic gates capacitively coupled to graphene to modulate the potential
landscape. When a gate-induced potential step is steep enough, disorder becomes
less important and the resistance across the step is in quantitative agreement
with predictions of Klein tunneling of Dirac fermions up to a small correction.
We also perform magnetoresistance measurements at low magnetic fields and
compare them to recent predictions.Comment: Major changes made: 1) Taking into account properly the contribution
of the resistance of monopolar junctions to the odd part of the resistance.
To better present the results we use a fitting parameter for the amplitude of
screening in graphene. 2) Wrong data for the diffusive model in figures 3, 9
and 10 was plotted in former version. 3) Figure 5 moved to EPAP
Dynamics of a qubit while simultaneously monitoring its relaxation and dephasing
Decoherence originates from the leakage of quantum information into external
degrees of freedom. For a qubit the two main decoherence channels are
relaxation and dephasing. Here, we report an experiment on a superconducting
qubit where we retrieve part of the lost information in both of these channels.
We demonstrate that raw averaging the corresponding measurement records
provides a full quantum tomography of the qubit state where all three
components of the effective spin-1/2 are simultaneously measured. From single
realizations of the experiment, it is possible to infer the quantum
trajectories followed by the qubit state conditioned on relaxation and/or
dephasing channels. The incompatibility between these quantum measurements of
the qubit leads to observable consequences in the statistics of quantum states.
The high level of controllability of superconducting circuits enables us to
explore many regimes from the Zeno effect to underdamped Rabi oscillations
depending on the relative strengths of driving, dephasing and relaxation.Comment: Supplemental videos can be found at
http://physinfo.fr/publications/Ficheux1710.html and supplemental information
can be found as an ancillary file on arxi
A compact design for the Josephson mixer: the lumped element circuit
We present a compact and efficient design in terms of gain, bandwidth and
dynamical range for the Josephson mixer, the superconducting circuit performing
three-wave mixing at microwave frequencies. In an all lumped-element based
circuit with galvanically coupled ports, we demonstrate non degenerate
amplification for microwave signals over a bandwidth up to 50 MHz for a power
gain of 20 dB. The quantum efficiency of the mixer is shown to be about 70
and its saturation power reaches dBm.Comment: 5 pages, 4 figure
Contact resistance and shot noise in graphene transistors
Potential steps naturally develop in graphene near metallic contacts. We
investigate the influence of these steps on the transport in graphene Field
Effect Transistors. We give simple expressions to estimate the
voltage-dependent contribution of the contacts to the total resistance and
noise in the diffusive and ballistic regimes.Comment: 6 pages, 4 figures; Figs 3 and 4 completed and appendix adde
Non-degenerate, three-wave mixing with the Josephson ring modulator
The Josephson ring modulator (JRM) is a device, based on Josephson tunnel
junctions, capable of performing non-degenerate mixing in the microwave regime
without losses. The generic scattering matrix of the device is calculated by
solving coupled quantum Langevin equations. Its form shows that the device can
achieve quantum-limited noise performance both as an amplifier and a mixer.
Fundamental limitations on simultaneous optimization of performance metrics
like gain, bandwidth and dynamic range (including the effect of pump depletion)
are discussed. We also present three possible integrations of the JRM as the
active medium in a different electromagnetic environment. The resulting
circuits, named Josephson parametric converters (JPC), are discussed in detail,
and experimental data on their dynamic range are found to be in good agreement
with theoretical predictions. We also discuss future prospects and requisite
optimization of JPC as a preamplifier for qubit readout applications.Comment: 21 pages, 16 figures, 4 table
Mouse adipose-derived stem cells undergo multilineage differentiation in vitro but primarily osteogenic and chondrogenic differentiation in vivo
Human, rat, and mouse studies have demonstrated the existence of a population of adipose-derived adult stem (ADAS) cells that can undergo multilineage differentiation in vitro. However, it remains unclear whether these cells maintain their multilineage potential in vivo. The aim of this study was to examine the in vitro and in vivo characteristics and behavior of a potential population of murine ADAS (muADAS) cells isolated from the visceral fat of the abdominal cavity of C57BL/10J mice. We used flow cytometry to examine the cells' expression of CD29, CD31, CD45, CD34, CD44, CD144, CD146, Flk1, and Sca-1. The isolated cell population was CD45 negative, which precludes contamination by hematopoietic cells, but was partially positive for Sca-1 and CD34: 2 stem-cell markers. After induction in conditioned medium, the muADAS cells gained the ability to undergo adipogenic, osteogenic, chondrogenic, myogenic, and hematopoietic differentiation in vitro. The muADAS cells readily differentiated to form bone and cartilage in vivo for up to 24 weeks, but their ability to regenerate muscle or reconstitute bone marrow was found to be limited. © Mary Ann Liebert, Inc
On the central quadric ansatz: integrable models and Painleve reductions
It was observed by Tod and later by Dunajski and Tod that the Boyer-Finley
(BF) and the dispersionless Kadomtsev-Petviashvili (dKP) equations possess
solutions whose level surfaces are central quadrics in the space of independent
variables (the so-called central quadric ansatz). It was demonstrated that
generic solutions of this type are described by Painleve equations PIII and
PII, respectively. The aim of our paper is threefold:
-- Based on the method of hydrodynamic reductions, we classify integrable
models possessing the central quadric ansatz. This leads to the five canonical
forms (including BF and dKP).
-- Applying the central quadric ansatz to each of the five canonical forms,
we obtain all Painleve equations PI - PVI, with PVI corresponding to the
generic case of our classification.
-- We argue that solutions coming from the central quadric ansatz constitute
a subclass of two-phase solutions provided by the method of hydrodynamic
reductions.Comment: 12 page
Observing quantum state diffusion by heterodyne detection of fluorescence
A qubit can relax by fluorescence, which prompts the release of a photon into
its electromagnetic environment. By counting the emitted photons, discrete
quantum jumps of the qubit state can be observed. The succession of states
occupied by the qubit in a single experiment, its quantum trajectory, depends
in fact on the kind of detector. How are the quantum trajectories modified if
one measures continuously the amplitude of the fluorescence field instead?
Using a superconducting parametric amplifier, we have performed heterodyne
detection of the fluorescence of a superconducting qubit. For each realization
of the measurement record, we can reconstruct a different quantum trajectory
for the qubit. The observed evolution obeys quantum state diffusion, which is
characteristic of quantum measurements subject to zero point fluctuations.
Independent projective measurements of the qubit at various times provide a
quantitative validation of the reconstructed trajectories. By exploring the
statistics of quantum trajectories, we demonstrate that the qubit states span a
deterministic surface in the Bloch sphere at each time in the evolution.
Additionally, we show that when monitoring fluorescence, coherent
superpositions are generated during the decay from excited to ground state.
Counterintuitively, measuring light emitted during relaxation can give rise to
trajectories with increased excitation probability.Comment: Supplementary material can be found in the ancillary sectio
Generating Entangled Microwave Radiation Over Two Transmission Lines
Using a superconducting circuit, the Josephson mixer, we demonstrate the
first experimental realization of spatially separated two-mode squeezed states
of microwave light. Driven by a pump tone, a first Josephson mixer generates,
out of quantum vacuum, a pair of entangled fields at different frequencies on
separate transmission lines. A second mixer, driven by a -phase shifted
copy of the first pump tone, recombines and disentangles the two fields. The
resulting output noise level is measured to be lower than for vacuum state at
the input of the second mixer, an unambiguous proof of entanglement. Moreover,
the output noise level provides a direct, quantitative measure of entanglement,
leading here to the demonstration of 6 Mebit.s (Mega entangled bits per
second) generated by the first mixer.Comment: 5 pages, 4 figures. Supplementary Information can be found here as an
ancillary fil
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