5,794 research outputs found
A spin quantum bit with ferromagnetic contacts for circuit QED
We theoretically propose a scheme for a spin quantum bit based on a double
quantum dot contacted to ferromagnetic elements. Interface exchange effects
enable an all electric manipulation of the spin and a switchable strong
coupling to a superconducting coplanar waveguide cavity. Our setup does not
rely on any specific band structure and can in principle be realized with many
different types of nanoconductors. This allows to envision on-chip single spin
manipulation and read-out using cavity QED techniques
Mesoscopic admittance of a double quantum dot
We calculate the mesoscopic admittance of a double quantum dot
(DQD),which can be measured directly using microwave techniques. This quantity
reveals spectroscopic information on the DQD and is also directly sensitive to
a Pauli spin blockade effect. We then discuss the problem of a DQD coupled to a
high quality photonic resonator. When the photon correlation functions can be
developed along a random-phase-approximation-like scheme, the response of the
resonator gives an access to
On the Kondo effect in carbon nanotubes at half halfing
In a single state of a quantum dot the Kondo effect arises due to the
spin-degeneracy, which is present if the dot is occupied with one electron (N =
1). The eigenstates of a carbon nanotube quantum dot possess an additional
orbital degeneracy leading to a four-fold shell pattern. This additional
degeneracy increases the possibility for the Kondo effect to appear. We revisit
the Kondo problem in metallic carbon nanotubes by linear and non-linear
transport measurement in this regime, in which the four-fold pattern is
present. We have analyzed the ground state of CNTs, which were grown by
chemical vapor deposition, at filling N = 1, N = 2, and N = 3. Of particular
interest is the half-filled shell, i.e. N = 2. In this case, the ground state
is either a paired electron state or a state for which the singlet and triplet
states are effectively degenerate, allowing in the latter case for the
appearance of the Kondo effect. We deduce numbers for the effective missmatch d
of the levels from perfect degeneracy and the exchange energy J. While d ~ 0.1
- 0.2 (in units of level spacing) is in agreement with previous work, the
exchange term is found to be surprisingly small: J < 0.02. In addition we
report on the observation of gaps, which in one case is seen at N = 3 and in
another is present over an extended sequence of levels.Comment: full paper including figures at:
http://www.unibas.ch/phys-meso/Research/Papers/2004/Kondo-4shell-SWNT.pd
Squeezing light with Majorana fermions
Coupling a semiconducting nanowire to a microwave cavity provides a powerfull
means to assess the presence or absence of isolated Majorana fermions in the
nanowire. These exotic bound states can cause a significant cavity frequency
shift but also a strong cavity nonlinearity leading for instance to light
squeezing. The dependence of these effects on the nanowire gate voltages gives
direct signatures of the unique properties of Majorana fermions, such as their
self-adjoint character and their exponential confinement.Comment: long version: 11 pages, 5 figure
Subradiant split Cooper pairs
We suggest a way to characterize the coherence of the split Cooper pairs
emitted by a double-quantum-dot based Cooper pair splitter (CPS), by studying
the radiative response of such a CPS inside a microwave cavity. The coherence
of the split pairs manifests in a strongly nonmonotonic variation of the
emitted radiation as a function of the parameters controlling the coupling of
the CPS to the cavity. The idea to probe the coherence of the electronic states
using the tools of Cavity Quantum Electrodynamics could be generalized to many
other nanoscale circuits.Comment: Main text + Supplemental material file (15 pages, 5 figures), to
appear in Physical Review Letter
Stamping single wall nanotubes for circuit quantum electrodynamics
We report on a dry transfer technique for single wall carbon nanotube devices
which allows to embed them in high finesse microwave cavity. We demonstrate the
ground state charge readout and a quality factor of about 3000 down to the
single photon regime. This technique allows to make devices such as double
quantum dots which could be instrumental for achieving the strong spin photon
coupling. It can easily be extended to generic carbon nanotube based microwave
devices.Comment: Version similar to the one accepte
Electrical Spin Injection in Multi-Wall carbon NanoTubes with transparent ferromagnetic contacts
We report on electrical spin injection measurements on MWNTs . We use a
ferromagnetic alloy PdNi with x 0.7 which allows to
obtain devices with resistances as low as 5.6 at 300 . The yield
of device resistances below 100 , at 300 , is around 50%. We
measure at 2 a hysteretic magneto-resistance due to the magnetization
reversal of the ferromagnetic leads. The relative difference between the
resistance in the antiparallel (AP) orientation and the parallel (P)
orientation is about 2%.Comment: submitted to APL version without figures version with figures
available on http://www.unibas.ch/phys-meso
The inter-relation between policy and practice for transitions from hospital to home: An ethnographic case study in Englandâs National Health Service
© 2014 Shaw et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.No abstract available (poster presentation)
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