779 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
All-optical non-demolition measurement of single-hole spin in a quantum-dot molecule
We propose an all-optical scheme to perform a non-demolition measurement of a
single hole spin localized in a quantum-dot molecule. The latter is embedded in
a microcavity and driven by two lasers. This allows to induce Raman transitions
which entangle the spin state with the polarization of the emitted photons. We
find that the measurement can be completed with high fidelity on a timescale of
100 ps, shorter than the typical T2. Furthermore, we show that the scheme can
be used to induce and observe spin oscillations without the need of
time-dependent magnetic fields
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
Optimizing photon indistinguishability in the emission from incoherently-excited semiconductor quantum dots
Most optical quantum devices require deterministic single-photon emitters.
Schemes so far demonstrated in the solid state imply an energy relaxation which
tends to spoil the coherent nature of the time evolution, and with it the
photon indistinguishability. We focus our theoretical investigation on
semiconductor quantum dots embedded in microcavities. Simple and general
relations are identified between the photon indistinguishability and the
collection efficiency. The identification of the key parameters and of their
interplay provides clear indications for the device optimization
Earthquake‐induced landslide scenarios for seismic microzonation. Application to the Accumoli area (Rieti, Italy)
Scenarios of earthquake-induced landslides are necessary for seismic microzonation (SM) studies since they must be integrated with the mapping of instability areas. The PARSIFAL (Probabilistic Approach to pRovide Scenarios of earthquake‐Induced slope FAiLures) approach provides extensive analyses, over tens to thousands of square kilometers, and is designed as a fully comprehensive methodology to output expected scenarios which depend on seismic input and saturation conditions. This allows to attribute a rating, in terms of severity level, to the landslide-prone slope areas in view of future engineering studies and designs. PARSIFAL takes into account first-time rock- and earth-slides as well as re-activations of existing landslides performing slope stability analyses of different failure mechanisms. The results consist of mapping earthquake-induced landslide scenarios in terms of exceedance probability of critical threshold values of co-seismic displacements (P[D≥Dc|a(t),ay]). PARSIFAL was applied in the framework of level 3 SM studies over the municipality area of Accumoli (Rieti, Italy), strongly struck by the 2016 seismic sequence of Central Apennines. The use of the PARSIFAL was tested for the first time to screen the Susceptibility Zones (ZSFR) from the Attention Zones (ZAFR) in the category of the unstable areas, according to the guidelines by Italian Civil Protection. The results obtained were in a GIS-based mapping representing the possibility for a landslide to be induced by an earthquake (with a return period of 475 years) in three different saturation scenarios (i.e. dry, average, full). Only 41% of the landslide-prone areas in the Municipality of Accumoli are existing events, while the remaining 59% is characterized by first-time earth- or rock-slides. In dry conditions, unstable conditions or P[D≥Dc|a(t),ay]>0 were for 54% of existing landslides, 17% of first-time rock-slides and 1% of first-time earth- slides. In full saturation conditions, the findings are much more severe since unstable conditions or P[D≥Dc|a(t),ay]>0 were found for 58% of the existing landslides and for more than 80% of first-time rock- and earth-slides. Moreover, comparison of the total area of the ZAFR versus ZSFR, resulted in PARSIFAL screening reducing of 22% of the mapped ZAFR
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
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