Enhanced coherence by coupling spins through a delocalized π-system: Vanadyl porphyrin dimers

Vanadium(IV) magnetic centers are prime candidates for molecular quantum units. One long-standing question is how to obtain a scaffold that connects multiple centers and allows two communication modalities: magnetic and electronic. We have synthesized and studied a selection of vanadyl porphyrin dimers as models of the most synthetically accessible linear porphyrin arrays. We show that a strongly π-conjugated backbone places the magnetic system in an intermediate regime dominated by exchange coupling (J) and protects the quantum coherence against electron pair flip-flop processes at low temperatures (<10 K). This result is a fundamental step toward the design of molecular materials for single-molecule devices controlled by microwaves with electrical readout

Magnetic edge states and coherent manipulation of graphene nanoribbons

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties. Graphene ribbons with nanometre-scale widths (nanoribbons) should exhibit half-metallicity and quantum confinement. Magnetic edges in graphene nanoribbons have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic and quantum computing devices. However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable. Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin–environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin–orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices

Face Mask Use and Control of Respiratory Virus Transmission in Households

Mask use is associated with low adherence, but adherent mask users are significantly protected against seasonal disease

Manipulating the coupling between electronic and spin degrees of freedom in molecules

The miniaturisation of semiconductors is running into physical limitations. In order to further enhance computational powers, reaching the atomic or molecular level is both necessary and inevitable. At the nanometre scale, the quantum properties of materials become important. These can be used for qubits in quantum computers, which are able to process information significantly faster than traditional counterparts. One approach towards such novel nanoelectronic devices is realised via molecular magnetic materials. Single-molecule magnets, which represent the smallest possible molecular magnetic structures, are currently being tested in such devices. However, the physics of these materials is not yet completely understood. The magnetic property of electrons, known as the electron spin, plays a crucial role here. It is furthermore very sensitive to its surroundings. Interactions with neighbouring nuclear spins, for instance, lead to decoherence, which translates to a loss of stored quantum information. In order to promote the development of new elements for nanoelectronics or qubits, it is therefore essential to unravel the couplings of the spins and their surroundings, and learn how to control and manipulate them. The present work focuses on how light, as an ultra-clean technique, can be used to manipulate the molecular spin states, and how magnetic centres interact when chemically attached to a graphene nanoribbon. We employ state-of-the-art electron spin resonance techniques and SQUID magnetometry to investigate the effect of light on a new cobalt valence tautomer, where we find an enhanced blocking temperature of a metastable light-excited state. Furthermore, we examine an Fe3Cr-based single-molecule magnet, where light causes a change in the giant spin. We then progress to graphene nanoribbons, which offer an interesting semiconducting backbone for magnetic molecules. Through a comprehensive analysis of spin-spin couplings in nitronyl-nitroxide graphene nanoribbons, we eventually prove the existence of an edge state, which allows for two-qubit applications.</p

Manipulating the coupling between electronic and spin degrees of freedom in molecules

The miniaturisation of semiconductors is running into physical limitations. In order to further enhance computational powers, reaching the atomic or molecular level is both necessary and inevitable. At the nanometre scale, the quantum properties of materials become important. These can be used for qubits in quantum computers, which are able to process information significantly faster than traditional counterparts. One approach towards such novel nanoelectronic devices is realised via molecular magnetic materials. Single-molecule magnets, which represent the smallest possible molecular magnetic structures, are currently being tested in such devices. However, the physics of these materials is not yet completely understood. The magnetic property of electrons, known as the electron spin, plays a crucial role here. It is furthermore very sensitive to its surroundings. Interactions with neighbouring nuclear spins, for instance, lead to decoherence, which translates to a loss of stored quantum information. In order to promote the development of new elements for nanoelectronics or qubits, it is therefore essential to unravel the couplings of the spins and their surroundings, and learn how to control and manipulate them. The present work focuses on how light, as an ultra-clean technique, can be used to manipulate the molecular spin states, and how magnetic centres interact when chemically attached to a graphene nanoribbon. We employ state-of-the-art electron spin resonance techniques and SQUID magnetometry to investigate the effect of light on a new cobalt valence tautomer, where we find an enhanced blocking temperature of a metastable light-excited state. Furthermore, we examine an Fe3Cr-based single-molecule magnet, where light causes a change in the giant spin. We then progress to graphene nanoribbons, which offer an interesting semiconducting backbone for magnetic molecules. Through a comprehensive analysis of spin-spin couplings in nitronyl-nitroxide graphene nanoribbons, we eventually prove the existence of an edge state, which allows for two-qubit applications.</p

Exploding the castle : rethinking how video games and game mechanics can shape the future of education

Comprend des références bibliographiques.Lacking a digital crystal ball, we cannot predict the future of education or the precise instructional role games will have going forward. Yet we can safely say that games will play some role in the future of K?12 and higher education, and members of the games community will have to choose between being passive observers or active, progressive contributors to the complex and often political process of weaving together pedagogy, technology, and culture. This will involve agreeing that games—or, more specifically, game mechanics and the engagement in joyful learning that they engender—are not only critical for shaping online and classroom instruction but also the evolution of schooling as a whole

Meningocele, a Protective Finding in Patient with Pulsatile Tinnitus and Brain Imaging Features Suggesting PTCS

Pulsatile tinnitus is a diagnostically challenging and commonly subjective symptom. It is a sensation of whooshing, whistling, humming that is unilateral or bilateral and is synchronized with heart beat. Origin may be arterial, arteriovenous or venous. It frequently resolves with distal pressure over the ipsilateral jugular vein. In pseudotumor cerebri syndrome (PTCS) origin of pulsatile tinnitus is likely venous due to turbulent flow through narrowed transverse venous sinus. Patients with PTCS typically present with headaches (90%) and transient visual obscurations (70%). Many patients have transverse sinus stenosis as result of chronic elevation of intracranial pressure which in turn leads to fibrosis resulting in narrowed appearance of dural sinus on venous imaging. Patients with PTCS can have abnormal findings on MRI including empty sella, transverse sinus stenosis, widened optic nerve sheath, and posterior globe flattening of orbits. In addition high intracranial pressure (ICP) can lead to spontaneous meningoceles, which could become a source of CSF leak

Singly- and Triply-Linked Magnetic Porphyrin Lanthanide Arrays

The introduction of paramagnetic metal centers into a conjugated π-system is a promising approach towards engineering spintronic materials. Here, we report an investigation of two types of spin-bearing dysprosium(III) and gadolinium(III) porphyrin dimers: singly meso-meso-linked dimers with twisted conformations and planar edge-fused ,meso,-linked tapes. The rare-earth spin centers sit out of the plane of the porphyrin, so that the singly linked dimers are chiral, and their enantiomers can be resolved, whereas the edge-fused tape complexes can be separated into syn and anti stereoisomers. We compare the crystal structures, UV-vis-NIR absorption spectra, electrochemistry, EPR spectroscopy and magnetic behavior of these complexes. Low temperature SQUID magnetometry measurements reveal intramolecular antiferromagnetic exchange coupling between the GdIII centers in the edge-fused dimers (syn isomer: J = –51 ±2 MHz; anti isomer: J = –19 ±3 MHz), whereas no exchange coupling is detected in the singly-linked twisted complex. The phase memory times, Tm, are in the range 8–10 µs at 3 K, which is long enough to test quantum computational schemes using microwave pulses. The syn and anti Dy2 edge-fused tapes both exhibit single molecule magnetic hysteresis cycles at temperatures below 0.5 K with slow magnetization dynamics

Impact of solvent mixture on iron nanoparticles generated by laser ablation

The present work reveals the structural and magnetic properties of iron oxide (FexOy) nanoparticles (NPs) prepared by femtosecond laser ablation. The FexOy-NPs were produced in solutions consisting of different ratios of water and acetone. Laser ablation in water yields agglomerates and that in acetone yields chain structures whereas that in water/acetone show a mixture of both. We observe significant fabrication dependent properties such as different crystallinities and magnetic behaviors. The structural characterization shows a change from iron (Fe) to a Fe xOy state of the NPs which depends on the solution composition. Furthermore, transmission electron microscopy measurements exhibit a broad particle size distribution in all samples but with significant differences in the mean sizes. Using magnetic measurements we show that nanoparticles fabricated in pure acetone have lower coercive fields which come along with a smaller mean particle size and therefore increasing superparamagnetic behavior. © 2014 SPIE