Molecular prototypes for spin-based CNOT quantum gates

We show that a chemically engineered structural asymmetry in [Tb2] molecular clusters renders the two weakly coupled Tb3+ spin qubits magnetically inequivalent. The magnetic energy level spectrum of these molecules meets then all conditions needed to realize a universal CNOT quantum gate.Comment: 4 pages, 4 figure

Origin of slow magnetic relaxation in Kramers ions with non-uniaxial anisotropy

Transition metal ions with long-lived spin states represent minimum size magnetic bits. Magnetic memory has often been associated with the combination of high spin and strong uniaxial magnetic anisotropy. Yet, slow magnetic relaxation has also been observed in some Kramers ions with dominant easy-plane magnetic anisotropy, albeit only under an external magnetic field. Here we study the spin dynamics of cobalt(II) ions in a model molecular complex. We show, by means of quantitative first-principles calculations, that the slow relaxation in this and other similar systems is a general consequence of time-reversal symmetry that hinders direct spin–phonon processes regardless of the sign of the magnetic anisotropy. Its magnetic field dependence is a subtle manifestation of electronuclear spin entanglement, which opens relaxation channels that would otherwise be forbidden but, at the same time, masks the relaxation phenomenon at zero field. These results provide a promising strategy to synthesize atom-size magnetic memories

Accurate measurements of small currents using a CCC with DC SQUID read out

The continuous miniaturisation in the semiconductor industry increases the importance of accurate measurement and control of very small currents. In the field of precision electrical measurements, cryogenic current comparators (CCCs) are used as extremely sensitive and accurate instruments for scaling currents. In an international co-operation project, a special CCC system is being developed, optimised for the measurement of extremely small currents to less than 1 pA (10−12 A). DC superconducting quantum interference device (SQUID) readout is used for monitoring the ampere-turn unbalance of the CCC. In this paper, we report on the accurate determination of the CCC and SQUID input coil inductances. Matching of these inductances is required for obtaining ultimate current resolution with the CCC. We find very good agreement between measurements of the CCC inductance at room temperature and at 4.2 K, and results from numerical calculations. The measured values for the input and mutual inductance of the SQUID sensor are in good agreement with the design values when the effect of the slit in the SQUID washer is correctly taken into account. Final current resolution of our measurement system is expected to be better than 1×10−15 A/√Hz for a CCC with 20,000 primary windings

Size and dimensionality effects in superconducting Mo thin films

Molybdenum is a low Tc, type I superconductor whose fundamental properties are poorly known. Its importance as an essential constituent of new high performance radiation detectors, the so-called transition edge sensors (TESs) calls for better characterization of this superconductor, especially in thin film form. Here we report on a study of the basic superconducting features of Mo thin films as a function of their thickness. The resistivity is found to rise and the critical temperature decreases on decreasing film thickness, as expected. More relevant, the critical fields along and perpendicular to the film plane are markedly different, thickness dependent and much larger than the thermodynamic critical field of Mo bulk. These results are consistent with a picture of type II 2D superconducting films, and allow estimates of the fundamental superconducting lengths of Mo. The role of morphology in determining the 2D and type II character of the otherwise type I molybdenum is discussed. The possible consequences of this behaviour on the performance of radiation detectors are also addresse

HVOF-Deposited WCCoCr as Replacement for Hard Cr in Landing Gear Actuators

WCCoCr coatings deposited by HVOF can replace hard Cr on landing gear components. Powders with two different WC particle sizes (micro and nano-) and geometries have been employed to study the effects on the coating’s properties. Moreover, coatings produced employing two sets of parameters resulting in high and low flame temperatures have been evaluated. Minor differences in microstructure and morphology were observed for the two powders employing the same spraying parameters, but the nano-sized powder exhibited a higher spraying efficiency. However, more significant microstructural changes result when the low- and high-energy spray parameters are used. Moreover, results of various tests which include adhesion, wear, salt fog corrosion resistance, liquid immersion, and axial fatigue strength, indicate that the coatings produced with high-energy flame are similar in behavior. On the other hand, the nanostructured low-energy flame coating exhibited a significantly lower salt fog corrosion resistanc

EURECA: European-Japanese microcalorimeter array

The EURECA project aims to demonstrate technological readiness of a micro-calorimeter array for application in future X-ray astronomy missions, like Constellation-X, EDGE, and XEUS. The prototype instrument consists of a 5 × 5 pixel array of TES-based micro-calorimeters read out by two SQUID-amplifier channels using frequency-domain-multiplexing (FDM) with digital base-band feedback. The detector array is cooled by a cryogen-free cryostat consisting of a pulse tube cooler and a two stage ADR. Initial tests of the system at the PTB beam line of the BESSY synchrotron showed stable performance and an X-ray energy resolution of 1.5 eV at 250 eV for read-out of one TES-pixel only. Next step is deployment of FDM to read-out the full array. Full performance demonstration is expected end 2008.This work was financially supported by the Dutch Organization for Scientific Research (NWO).Peer Reviewe

[email protected]; phone +31 30 2535710; fax +31 30 2540860, www.sron.nl Space Telescopes and Instrumentation

ABSTRACT The EURECA (EURopean-JapanEse Calorimeter Array) project aims to demonstrate the science performance and technological readiness of an imaging X-ray spectrometer based on a micro-calorimeter array for application in future X-ray astronomy missions, like Constellation-X and XEUS. The prototype instrument consists of a 5 x 5 pixel array of TES-based micro-calorimeters read out by by two SQUID-amplifier channels using frequency-domain-multiplexing (FDM). The SQUID-amplifiers are linearized by digital base-band feedback. The detector array is cooled in a cryogenfree cryostat consisting of a pulse tube cooler and a two stage ADR. A European-Japanese consortium designs, fabricates, and tests this prototype instrument. This paper describes the instrument concept, and shows the design and status of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, AC-bias sources, digital electronics, etc. Initial tests of the system at the PTB beam line of the BESSY synchrotron showed stable performance and an X-ray energy resolution of 1.58 eV at 250 eV and 2.5 eV @ 5.9 keV for the read-out of one TES-pixel only. Next step is deployment of FDM to read-out the full array. Full performance demonstration is expected mid 2009

Pasados y presente. Estudios para el profesor Ricardo García Cárcel

Ricardo García Cárcel (Requena, 1948) estudió Historia en Valencia bajo el magisterio de Joan Reglà, con quien formó parte del primer profesorado de historia moderna en la Universidad Autónoma de Barcelona. En esta universidad, desde hace prácticamente cincuenta años, ha desarrollado una extraordinaria labor docente y de investigación marcada por un sagaz instinto histórico, que le ha convertido en pionero de casi todo lo que ha estudiado: las Germanías, la historia de la Cataluña moderna, la Inquisición, las culturas del Siglo de Oro, la Leyenda Negra, Felipe II, Felipe V, Austrias y Borbones, la guerra de la Independencia, la historia cultural, los mitos de la historia de España... Muy pocos tienen su capacidad para reflexionar, ordenar, analizar, conceptualizar y proponer una visión amplia y llena de matices sobre el pasado y las interpretaciones historiográficas. A su laboriosidad inimitable se añade una dedicación sin límites en el asesoramiento de alumnos e investigadores e impulsando revistas, dosieres, seminarios o publicaciones colectivas. Una mínima correspondencia a su generosidad lo constituye este volumen a manera de ineludible agradecimiento

Origin of slow magnetic relaxation in Kramers ions with non-uniaxial anisotropy

Transition metal ions with long-lived spin states represent minimum size magnetic bits. Magnetic memory has often been associated with the combination of high spin and strong uniaxial magnetic anisotropy. Yet, slow magnetic relaxation has also been observed in some Kramers ions with dominant easy-plane magnetic anisotropy, albeit only under an external magnetic field. Here we study the spin dynamics of cobalt(II) ions in a model molecular complex. We show, by means of quantitative first-principles calculations, that the slow relaxation in this and other similar systems is a general consequence of time-reversal symmetry that hinders direct spin-phonon processes regardless of the sign of the magnetic anisotropy. Its magnetic field dependence is a subtle manifestation of electronuclear spin entanglement, which opens relaxation channels that would otherwise be forbidden but, at the same time, masks the relaxation phenomenon at zero field. These results provide a promising strategy to synthesize atom-size magnetic memories. © 2014 Macmillan Publishers Limited. All rights reserved.The research reported here was supported by the Spanish Ministerio de Economía y Competitividad (grants MAT2012-38318-C03, CTQ2011-23862-C02-01 and MAT2011-23861), Gobierno de Aragón (grants E98-‘MOLCHIP’ and E33) and the Generalitat de Catalunya authority (2009SGR-1459). S.G.C. thanks the Spanish Ministerio de Educación, Cultura y Deporte for a predoctoral fellowship.Peer Reviewe