ABSTRACT
Superconducting circuits are a strong contender for realizing quantum computing systems and are also successfully used to study quantum optics and hybrid quantum systems. However, their cryogenic operation temperatures and the current lack of coherence-preserving microwave-to-optical conversion solutions have hindered the realization of superconducting quantum networks spanning different cryogenic systems or larger distances. Here, we report the successful operation of a cryogenic waveguide coherently linking transmon qubits located in two dilution refrigerators separated by a physical distance of five meters. We transfer qubit states and generate entanglement on demand with average transfer and target state fidelities of 85.8% and 79.5%, respectively, between the two nodes of this elementary network. Cryogenic microwave links provide an opportunity to scale up systems for quantum computing and create local area superconducting quantum communication networks over length scales of at least tens of meters.
ABSTRACT
The conversion of charge currents into spin currents in nonmagnetic conductors is a hallmark manifestation of spin-orbit coupling that has important implications for spintronic devices. Here we report the measurement of the interfacial spin accumulation induced by the spin Hall effect in Pt and W thin films using magneto-optical Kerr microscopy. We show that the Kerr rotation has opposite sign in Pt and W and scales linearly with current density. By comparing the experimental results with ab initio calculations of the spin Hall and magneto-optical Kerr effects, we quantitatively determine the current-induced spin accumulation at the Pt interface as 5×10^{-12} µ_{B} A^{-1} cm^{2} per atom. From thickness-dependent measurements, we determine the spin diffusion length in a single Pt film to be 11±3 nm, which is significantly larger compared to that of Pt adjacent to a magnetic layer.
ABSTRACT
Ultrafast spin currents induced by femtosecond laser excitation of ferromagnetic metals have been found to contribute to sub-picosecond demagnetization, and to cause a transient enhancement of the magnetization of the bottom Fe layer in a Ni/Ru/Fe layered structure. We analyze the ultrafast magnetization dynamics in such layered structures by element- and femtosecond time-resolved x-ray magnetic circular dichroism, for different Ni and Fe layer thicknesses, Ru and Ta interlayers, and by varying the pump laser fluence. While we do not observe the transient enhancement of the magnetization in Ni/Ru/Fe discovered previously, we do find a reduced demagnetization of the Fe layer compared to a Ni/Ta/Fe layered structure. In the latter, the spin-scattering Ta layer suppresses spin currents from the Ni layer into Fe, consistent with previous results. Any spin current arriving in the lower Fe layer will counteract other, local demagnetization mechanisms such as phonon-mediated spin-flip scattering. We find by increasing the Ni and Fe layer thicknesses in Ni/Ru/Fe a decreasing effect of spin currents on the buried Fe layer, consistent with a mean free path of the laser-induced spin currents of just a few nm. Our results suggest that in order to utilize ultrafast spin currents in an efficient manner, the sample design has to be optimized with these considerations in mind, and further studies clarifying the role of interfaces in the employed layered structures are needed.
ABSTRACT
Hydrocarbons inherently present in standard high-vacuum scanning electron microscopes can be favorably used for co-deposition with functional molecules injected into the chamber. By varying the beam exposure pulse time the carbon content incorporated into the deposit can be tuned. In the particular case when the hydrocarbons are provided by surface diffusion, the composition depends also on the size of the final deposits. This dependency can be used as an additional parameter, besides the beam pulse time, in order to tune the metal/matrix ratio and to obtain new nanoscale materials with tailored physical properties. We present and discuss experimental results on composition tunability by pulsed electron-beam deposition for the two-adsorbate system Co2(CO)8/hydrocarbon and their use in fabricating Hall nanosensors of cobalt-carbon nanocomposite material with enhanced magnetic sensitivity and high magnetic spatial resolution.
