2,150 research outputs found
Use of dynamical coupling for improved quantum state transfer
We propose a method to improve quantum state transfer in transmission lines.
The idea is to localize the information on the last qubit of a transmission
line, by dynamically varying the coupling constants between the first and the
last pair of qubits. The fidelity of state transfer is higher then in a chain
with fixed coupling constants. The effect is stable against small fluctuations
in the system parameters.Comment: 5 pages, 7 figure
Broadening of Andreev-Bound States in d_{x^2-y^2} superconductors
We investigate the broadening of the bound states at an interface of an
unconventional superconductor by bulk impurity scattering. We use the
quasiclassical theory and include impurity scattering in the Born and in the
unitarity limit. The broadening of bound states due to unitary scatterers is
shown to be substantially weaker than in the Born limit. We study various model
geometries and calculate the temperature dependence of the Josephson critical
current in the presence of these impurity-broadened bound states.Comment: 6 page including 7 figures, submitted to Phys. Rev.
Role of interference in quantum state transfer through spin chains
We examine the role that interference plays in quantum state transfer through
several types of finite spin chains, including chains with isotropic Heisenberg
interaction between nearest neighbors, chains with reduced coupling constants
to the spins at the end of the chain, and chains with anisotropic coupling
constants. We evaluate quantitatively both the interference corresponding to
the propagation of the entire chain, and the interference in the effective
propagation of the first and last spins only, treating the rest of the chain as
black box. We show that perfect quantum state transfer is possible without
quantum interference, and provide evidence that the spin chains examined
realize interference-free quantum state transfer to a good approximation.Comment: 10 figure
2015 Update on Acute Adverse Reactions to Gadolinium based Contrast Agents in Cardiovascular MR. Large Multi-National and Multi-Ethnical Population Experience With 37788 Patients From the EuroCMR Registry
Objectives: Specifically we aim to demonstrate that the results of our earlier safety data hold true in this much larger multi-national and multi-ethnical population. Background: We sought to re-evaluate the frequency, manifestations, and severity of acute adverse reactions associated with administration of several gadolinium- based contrast agents during routine CMR on a European level. Methods: Multi-centre, multi-national, and multi-ethnical registry with consecutive enrolment of patients in 57 European centres. Results: During the current observation 37788 doses of Gadolinium based contrast agent were administered to 37788 patients. The mean dose was 24.7Â ml (range 5â80Â ml), which is equivalent to 0.123Â mmol/kg (range 0.01 - 0.3Â mmol/kg). Forty-five acute adverse reactions due to contrast administration occurred (0.12Â %). Most reactions were classified as mild (43 of 45) according to the American College of Radiology definition. The most frequent complaints following contrast administration were rashes and hives (15 of 45), followed by nausea (10 of 45) and flushes (10 of 45). The event rate ranged from 0.05Â % (linear non-ionic agent gadodiamide) to 0.42Â % (linear ionic agent gadobenate dimeglumine). Interestingly, we also found different event rates between the three main indications for CMR ranging from 0.05Â % (risk stratification in suspected CAD) to 0.22Â % (viability in known CAD). Conclusions: The current data indicate that the results of the earlier safety data hold true in this much larger multi-national and multi-ethnical population. Thus, the âoff-labelâ use of Gadolinium based contrast in cardiovascular MR should be regarded as safe concerning the frequency, manifestation and severity of acute events
Josephson Effect in a Coulomb-blockaded SINIS Junction
The problem of Josephson current through Coulomb-blocked nanoscale
superconductor-normal-superconductor structure with tunnel contacts is
reconsidered. Two different contributions to the phase-biased supercurrent are
identified, which are dominant in the limits of weak and strong Coulomb
interaction. Full expression for the free energy valid at arbitrary Coulomb
strength is found. The current derived from this free energy interpolates
between known results for weak and strong Coulomb interaction as phase bias
changes from 0 to pi. In the broad range of Coulomb strength the current-phase
relation is substantially non-sinusoidal and qualitatively different from the
case of semi-ballistic SNS junctions. Coulomb interaction leads to appearance
of a local minimum in the current at some intermediate value of phase
difference applied to the junction.Comment: 5 pages, 2 EPS figures, JETP Letters style file include
Electric instability in superconductor-normal conductor ring
Non-linear electrodynamics of a ring-shaped Andreev interferometer
(superconductor-normal conductor-superconductor hybrid structure) inductively
coupled to a circuit of the dissipative current is investigated. The
current-voltage characteristics (CVC) is demonstrated to be a series of loops
with several branches intersecting in the CVC origin. The sensitivity of the
transport current to a change of the applied external magnetic flux can be
comparable to the one of the conventional SQUID's. Spontaneous arising of
coupled non-linear oscillations of the transport current, the Josephson current
and the magnetic flux in Andreev interferometers are also predicted and
investigated. The frequency of these oscillations can be varied in a wide
range, while the maximal frequency can reach
.Comment: 4 pages, 4 figure
Electron-phonon coupling in crystalline organic semiconductors: Microscopic evidence for nonpolaronic charge carriers
We consider electron(hole)-phonon coupling in crystalline organic
semiconductors, using naphthalene for our case study. Employing a
first-principles approach, we compute the changes in the self-consistent
Kohn-Sham potential corresponding to different phonon modes and go on to obtain
the carrier-phonon coupling matrix elements (vertex functions). We then
evaluate perturbatively the quasiparticle spectral residues for electrons at
the bottom of the lowest-unoccupied- (LUMO) and holes at the top of the
highest-occupied (HOMO) band, respectively obtaining and
. Along with the widely accepted notion that the
carrier-phonon coupling strengths in polyacenes decrease with increasing
molecular size, our results provide a strong microscopic evidence for the
previously conjectured nonpolaronic nature of band-like carriers in these
systems.Comment: final, published versio
Positive cross-correlations in a three-terminal quantum dot with ferromagnetic contacts
We study current fluctuations in an interacting three-terminal quantum dot
with ferromagnetic leads. For appropriately polarized contacts, the transport
through the dot is governed by a novel dynamical spin blockade, i.e., a
spin-dependent bunching of tunneling events not present in the paramagnetic
case. This leads for instance to positive zero-frequency cross-correlations of
the currents in the output leads even in the absence of spin accumulation on
the dot. We include the influence of spin-flip scattering and identify
favorable conditions for the experimental observation of this effect with
respect to polarization of the contacts and tunneling rates.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Dynamic method to distinguish between left- and right-handed chiral molecules
We study quantum systems with broken symmetry that can be modelled as cyclic
three-level atoms with coexisting one- and two-photon transitions. They can be
selectively optically excited to any state. As an example, we show that left-
and right-handed chiral molecules starting in the same initial states can
evolve into different final states by a purely dynamic transfer process. That
means, left- and right-handed molecules can be distinguished purely
dynamically.Comment: 4 pages, submitted to Phys. Rev.
- âŠ