629 research outputs found
Towards the chemical tuning of entanglement in molecular nanomagnets
Antiferromagnetic spin rings represent prototypical realizations of highly
correlated, low-dimensional systems. Here we theoretically show how the
introduction of magnetic defects by controlled chemical substitutions results
in a strong spatial modulation of spin-pair entanglement within each ring.
Entanglement between local degrees of freedom (individual spins) and collective
ones (total ring spins) are shown to coexist in exchange-coupled ring dimers,
as can be deduced from general symmetry arguments. We verify the persistence of
these features at finite temperatures, and discuss them in terms of
experimentally accessible observables.Comment: 5 pages, 4 figure
Quantum-gate implementation in permanently coupled AF spin rings without need of local fields
We propose a scheme for the implementation of quantum gates which is based on
the qubit encoding in antiferromagnetic molecular rings. We show that a proper
engineering of the intercluster link would result in an effective coupling that
vanishes as far as the system is kept in the computational space, while it is
turned on by a selective excitation of specific auxiliary states. These are
also shown to allow the performing of single- and two-qubit gates without an
individual addressing of the rings by means of local magnetic fields.Comment: To appear in Physical Review Letter
Entangled photon pairs from a quantum dot cascade decay: the effect of time-reordering
Coulomb interactions between confined carriers remove degeneracies in the
excitation spectra of quantum dots. This provides a which path information in
the cascade decay of biexcitons, thus spoiling the energy-polarization
entanglement of the emitted photon pairs. We theoretically analyze a strategy
of color coincidence across generation (AG), recently proposed as an
alternative to the previous, within generation (WG) approach. We simulate the
system dynamics and compute the correlation functions within the density-matrix
formalism. This allows to estimate quantities that are accessible by a
polarization-tomography experiment, and that enter the expression of the
two-photon concurrence. We identify the optimum parameters within the AG
approach, and the corresponding maximum values of the concurrence
Spin-Electric Coupling in Molecular Magnets
We study the triangular antiferromagnet Cu in external electric fields,
using symmetry group arguments and a Hubbard model approach. We identify a
spin-electric coupling caused by an interplay between spin exchange, spin-orbit
interaction, and the chirality of the underlying spin texture of the molecular
magnet. This coupling allows for the electric control of the spin (qubit)
states, e.g. by using an STM tip or a microwave cavity. We propose an
experimental test for identifying molecular magnets exhibiting spin-electric
effects.Comment: 5 pages, 3 figure
Experimental determination of thickness influence on compressive residual strength of impacted carbon/epoxy laminate
Abstract: An experimental campaign was performed on 5.5 mm thick carbon/epoxy specimens and results were compared with data obtained in a previous work to understand thickness influence on material mechanical characteristics. In particular, this campaign consists of two different steps: impacts tests, performed by means of a modified Charpy pendulum, and Compression After Impact (CAI), using Wyoming Combined Loading Compression (CLC) test method. Impacts were performed on twenty cross-ply specimens with different energies and impact location. Other 5 specimens were tested only in compression. Non Destructive Inspections (NDI) by Ultrasonic Test (UT) were performed on impacted and pristine specimens, in order to understand damage size and correlate it with residual strength results. During CLC tests, compression strength and Young modulus values were acquired
Microwave dual-mode resonators for coherent spin-photon coupling
We implement superconducting Yttrium barium copper oxide planar resonators with two fundamental modes for circuit quantum electrodynamics experiments. We first demonstrate good tunability in the resonant microwave frequencies and in their interplay, as emerges from the dependence of the transmission spectra on the device geometry. We then investigate the magnetic coupling of the resonant modes with bulk samples of 2,2-diphenyl-1-picrylhydrazyl organic radical spins. The transmission spectroscopy performed at low temperature shows that the coherent spin-photon coupling regime with the spin ensembles can be achieved by each of the resonator modes. The analysis of the results within the framework of the input-output formalism and by means of entropic measures demonstrates coherent mixing of the degrees of freedom corresponding to two remote spin ensembles and, with a suitable choice of the geometry, the approaching of a regime with spin-induced mixing of the two photon modes
Electrical control of the exciton-biexciton splitting in a single self-assembled InGaAs quantum dots
We report on single InGaAs quantum dots embedded in a lateral electric field
device. By applying a voltage we tune the neutral exciton transition into
resonance with the biexciton using the quantum confined Stark effect. The
results are compared to theoretical calculations of the relative energies of
exciton and biexciton. Cascaded decay from the manifold of single
exciton-biexciton states has been predicted to be a new concept to generate
entangled photon pairs on demand without the need to suppress the fine
structures splitting of the neutral exciton
DNS of a variable density jet in the supercritical thermodynamic state
Cryogenic rocket engines, advanced gas turbines and diesel engines are characterized by the injection of a liquid fuel into a high temperature and pressure chamber. Typically the fuel is injected at high enough pressure to be close or above the critical pressure. In these conditions the behavior of the fluid differs strongly from that of a perfect gas. It exhibits large variations of thermodynamic and transport properties also for small temperature changes, with significant effects on mixing and combustion processes. In this context an appropriate numerical simulation should take into account such thermodynamic phenomena via suitable equation of state and transport properties relations
Spin electric effects in molecular antiferromagnets
Molecular nanomagnets show clear signatures of coherent behavior and have a
wide variety of effective low-energy spin Hamiltonians suitable for encoding
qubits and implementing spin-based quantum information processing. At the
nanoscale, the preferred mechanism for control of quantum systems is through
application of electric fields, which are strong, can be locally applied, and
rapidly switched. In this work, we provide the theoretical tools for the search
for single molecule magnets suitable for electric control. By group-theoretical
symmetry analysis we find that the spin-electric coupling in triangular
molecules is governed by the modification of the exchange interaction, and is
possible even in the absence of spin-orbit coupling. In pentagonal molecules
the spin-electric coupling can exist only in the presence of spin-orbit
interaction. This kind of coupling is allowed for both and
spins at the magnetic centers. Within the Hubbard model, we find a relation
between the spin-electric coupling and the properties of the chemical bonds in
a molecule, suggesting that the best candidates for strong spin-electric
coupling are molecules with nearly degenerate bond orbitals. We also
investigate the possible experimental signatures of spin-electric coupling in
nuclear magnetic resonance and electron spin resonance spectroscopy, as well as
in the thermodynamic measurements of magnetization, electric polarization, and
specific heat of the molecules.Comment: 31 pages, 24 figure
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