Granular aluminium nanojunction fluxonium qubit.

Mesoscopic Josephson junctions, consisting of overlapping superconducting electrodes separated by a nanometre-thin oxide layer, provide a precious source of nonlinearity for superconducting quantum circuits. Here we show that in a fluxonium qubit, the role of the Josephson junction can also be played by a lithographically defined, self-structured granular aluminium nanojunction: a superconductor-insulator-superconductor Josephson junction obtained in a single-layer, zero-angle evaporation. The measured spectrum of the resulting qubit, which we nickname gralmonium, is indistinguishable from that of a standard fluxonium. Remarkably, the lack of a mesoscopic parallel plate capacitor gives rise to an intrinsically large granular aluminium nanojunction charging energy in the range of tens of gigahertz, comparable to its Josephson energy. We measure coherence times in the microsecond range and we observe spontaneous jumps of the value of the Josephson energy on timescales from milliseconds to days, which offers a powerful diagnostics tool for microscopic defects in superconducting materials.

Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm.

Quantum algorithms use the principles of quantum mechanics, such as, for example, quantum superposition, in order to solve particular problems outperforming standard computation. They are developed for cryptography, searching, optimization, simulation, and solving large systems of linear equations. Here, we implement Grover's quantum algorithm, proposed to find an element in an unsorted list, using a single nuclear 3/2 spin carried by a Tb ion sitting in a single molecular magnet transistor. The coherent manipulation of this multilevel quantum system (qudit) is achieved by means of electric fields only. Grover's search algorithm is implemented by constructing a quantum database via a multilevel Hadamard gate. The Grover sequence then allows us to select each state. The presented method is of universal character and can be implemented in any multilevel quantum system with nonequal spaced energy levels, opening the way to novel quantum search algorithms.

Landau-Zener Transition in a Continuously Measured Single-Molecule Spin Transistor.

We monitor the Landau-Zener dynamics of a single-ion magnet inserted into a spin-transistor geometry. For increasing field-sweep rates, the spin reversal probability shows increasing deviations from that of a closed system. In the low-conductance limit, such deviations are shown to result from a dephasing process. In particular, the observed behaviors are successfully simulated by means of an adiabatic master equation, with time averaged dephasing (Lindblad) operators. The time average is tentatively interpreted in terms of the finite time resolution of the continuous measurement.

Phase dependence of microwave-assisted switching of a single magnetic nanoparticle.

Microwave-assisted switching of the magnetization is an efficient way to reduce the magnetic field required to reverse the magnetization of nanostructures. Here, the phase sensitivity of microwave-assisted switching of an individual cobalt nanoparticle is studied using a pump-probe technique. The pump microwave pulse prepares an initial state of the magnetization, and the probe pulse tests its stability against switching. Precession states are established, which are stable against switching. Their basin of attraction is measured and is in qualitative agreement with numerical macrospin calculations. The damping parameter is evaluated using the variable delay pump-probe technique.

Interplay of the Kondo effect and strong spin-orbit coupling in multihole ultraclean carbon nanotubes.

We report on cotunneling spectroscopy magnetoconductance measurements of multihole ultraclean carbon nanotube quantum dots in the SU(4) Kondo regime with strong spin-orbit coupling. Successive shells show a gradual weakening of the Kondo effect with respect to the spin-orbital splittings, leading to an evolution from SU(4) to SU(2) symmetry with a suppressed conductance at half-shell filling. The extracted energy level spectrum, overall consistent with negligible disorder in the nanotube, shows in the half filled case large renormalizations due to Coulombian effects.

Electrical readout of individual nuclear spin trajectories in a single-molecule magnet spin transistor.

We present the electrical readout of time trajectories obtained from an isolated nuclear spin. The device, a TbPc(2) single-molecule magnet spin transistor, detects the four different nuclear spin states of the Tb(3+) ion with fidelities better than 69%, allowing us to measure individual relaxation times (T(1)) of several tens of seconds. A good agreement with quantum Monte Carlo simulations suggests that the relaxation times are limited by the current tunneling through the transistor, which opens up the possibility to tune T(1) electrically by means of bias and gate voltages.

Supramolecular spin valves.

Magnetic molecules are potential building blocks for the design of spintronic devices. Moreover, molecular materials enable the combination of bottom-up processing techniques, for example with conventional top-down nanofabrication. The development of solid-state spintronic devices based on the giant magnetoresistance, tunnel magnetoresistance and spin-valve effects has revolutionized magnetic memory applications. Recently, a significant improvement of the spin-relaxation time has been observed in organic semiconductor tunnel junctions, single non-magnetic molecules coupled to magnetic electrodes have shown giant magnetoresistance and hybrid devices exploiting the quantum tunnelling properties of single-molecule magnets have been proposed. Herein, we present an original spin-valve device in which a non-magnetic molecular quantum dot, made of a single-walled carbon nanotube contacted with non-magnetic electrodes, is laterally coupled through supramolecular interactions to TbPc(2) single-molecule magnets (Pc=phthalocyanine). Their localized magnetic moments lead to a magnetic field dependence of the electrical transport through the single-walled carbon nanotube, resulting in magnetoresistance ratios up to 300% at temperatures less than 1 K. We thus demonstrate the functionality of a supramolecular spin valve without magnetic leads. Our results open up prospects of new spintronic devices with quantum properties.

Bistable coupling states measured on single Co nanoclusters deposited on CoO(111).

We describe novel features of the induced magnetic anisotropy in Co nanoclusters coupled with a CoO(111) layer. Individual cluster magnetism was studied using new microbridge superconducting quantum interference devices. Intrinsically, the Co clusters are single domains with an effective anisotropy constant K(F)≈1.5×10(6) erg·cm(-3). A bistable state of the ferromagnetic-antiferromagnetic coupling is revealed, with a maximum bias systematically observed along CoO[10 ̅1] and an interfacial coupling energy of 0.9 erg·cm(-2). The small bias observed in cluster assembly results from an averaging over the two opposite stable states.

Magneto-Coulomb effect in carbon nanotube quantum dots filled with magnetic nanoparticles.

Electrical transport measurements of carbon nanotubes filled with magnetic iron nanoparticles are reported. Low-temperature (40 mK) magnetoresistance measurements showed conductance hysteresis with sharp jumps at the switching fields of the nanoparticles. Depending on the gate voltage, positive or negative hysteresis was observed. The results are explained in terms of a magneto-Coulomb effect: The spin flip of the iron island at a nonzero magnetic field causes a shift of the chemical potential induced by the change of Zeeman energy; i.e., an effective charge variation is detected by the nanotube quantum dot.

Propagation of spin information at the supramolecular scale through heteroaromatic linkers.

We report an in-depth study on how spin information propagates at supramolecular scale through a family of heteroaromatic linkers. By density-functional theory calculations, we rationalize the behavior of a series of Cr7Ni dimers for which we are able to systematically change the aromatic linker thus tuning the strength of the magnetic interaction, as experimentally shown by low temperature micro-SQUID and specific heat measurements. We also predict a cos2 dependence of the magnetic coupling on the twisting angle between the aromatic cycles in bicyclic linkers, a mechanism parallel to charge transport on similar systems [L. Venkataraman et al., Nature (London) 442, 904 (2006)].

Reducing the impact of radioactivity on quantum circuits in a deep-underground facility.

As quantum coherence times of superconducting circuits have increased from nanoseconds to hundreds of microseconds, they are currently one of the leading platforms for quantum information processing. However, coherence needs to further improve by orders of magnitude to reduce the prohibitive hardware overhead of current error correction schemes. Reaching this goal hinges on reducing the density of broken Cooper pairs, so-called quasiparticles. Here, we show that environmental radioactivity is a significant source of nonequilibrium quasiparticles. Moreover, ionizing radiation introduces time-correlated quasiparticle bursts in resonators on the same chip, further complicating quantum error correction. Operating in a deep-underground lead-shielded cryostat decreases the quasiparticle burst rate by a factor thirty and reduces dissipation up to a factor four, showcasing the importance of radiation abatement in future solid-state quantum hardware.

Entanglement in supramolecular spin systems of two weakly coupled antiferromagnetic rings (purple-Cr7Ni).

We characterize supramolecular magnetic structures, consisting of two weakly coupled antiferromagnetic rings, by low-temperature specific heat, susceptibility, magnetization and electron paramagnetic resonance measurements. Intra- and inter-ring interactions are modeled through a microscopic spin-Hamiltonian approach that reproduces all the experimental data quantitatively and legitimates the use of an effective two-qubit picture. Spin entanglement between the rings is experimentally demonstrated through magnetic susceptibility below 50 mK and theoretically quantified by the concurrence.

Electronic and magnetic study of polycationic Mn(12) single-molecule magnets with a ground spin state S = 11.

The preparation, magnetic characterization, and X-ray structures of two polycationic Mn(12) single-molecule magnets [Mn(12)O(12)(bet)(16)(EtOH)(4)](PF(6))(14).4CH(3)CN.H(2)O (1) and [Mn(12)O(12)(bet)(16)(EtOH)(3)(H(2)O)](PF(6))(13)(OH).6CH(3)CN.EtOH.H(2)O (2) (bet = betaine = (CH(3))(3)N(+)-CH(2)-CO(2)(-)) are reported. 1 crystallizes in the centrosymmetric P2/c space group and presents a (0:2:0:2) arrangement of the EtOH molecules in its structure. 2 crystallizes in the noncentrosymmetric P4 space group with two distinct Mn(12) polycations, [Mn(12)O(12)(bet)(16)(EtOH)(2)(H(2)O)(2)](14+) (2A) and [Mn(12)O(12)(bet)(16)(EtOH)(4)](14+) (2B) per unit cell. 2A and 2B show a (1:1:1:1) distribution of the coordinated solvent molecules. Interestingly, bond valence sum calculations extracted from X-ray diffraction data indicate the presence of two Mn(2+) ions in the Mn(12) core for both 1 and 2. This finding is confirmed by X-ray absorption spectroscopy (XAS) measurements. A complete magnetic characterization, including subkelvin micro-SQUID magnetometry and inelastic neutron scattering (INS) measurements, permits to extract the parameters of the giant spin Hamiltonian of these polycations. Compared with the archetypal Mn(12) acetate, an increase in the value of the ground spin state from S = 10 to S = 11 together with a decrease in the effective energy barrier, is observed for 1 and 2. Such a result is consistent with the reduction of two Mn(3+) to the less anisotropic Mn(2+) ion in the structures.

Antimalarial activity of tigecycline, a novel glycylcycline antibiotic.

Tigecycline is a novel glycylcycline antibiotic with a broad antibacterial spectrum. Tigecycline was tested with 66 clinical isolates of Plasmodium falciparum from Bangladesh using the histidine-rich protein 2 in vitro drug susceptibility assay. The 50% and 90% inhibitory concentrations of tigecycline were 699 (95% confidence interval, 496 to 986) and 5,905 nM (4,344 to 8,028). Tigecycline shows no activity correlation with traditional antimalarials and has substantial antimalarial activity on its own.

Contacting individual Fe(110) dots in a single electron-beam lithography step.

We report on a new approach, entirely based on an electron-beam lithography technique, to contact electrically, in a four-probe scheme, single nanostructures obtained by self-assembly. In our procedure, nanostructures of interest are located and contacted in the same fabrication step. This technique has been developed to study the field-induced reversal of an internal component of an asymmetric Bloch domain wall observed in elongated structures such as Fe(110) dots. We have focused on the control, using an external magnetic field, of the magnetization orientation within Néel caps that terminate the domain wall at both interfaces. Preliminary magneto-transport measurements are discussed demonstrating that single Fe(110) dots have been contacted.

Transport spectroscopy of single Pt impurities in silicon using Schottky barrier MOSFETs.

We investigate low temperature electron transport in silicon Schottky barrier metal-oxide-semiconductor field-effect transistors (MOSFETs), which consist of PtSi metallic source/drain electrodes. Measurements are made on approximately 23 inversion layers and resonances attributed to single impurities close to the metal/semiconductor interface are observed. We ascribe these impurities to Pt atoms that have diffused into the semiconductor channel from the contacts.

Circuit quantum electrodynamics of granular aluminum resonators.

Granular aluminum (grAl) is a promising high kinetic inductance material for detectors, amplifiers, and qubits. Here we model the grAl structure, consisting of pure aluminum grains separated by thin aluminum oxide barriers, as a network of Josephson junctions, and we calculate the dispersion relation and nonlinearity (self-Kerr and cross-Kerr coefficients). To experimentally study the electrodynamics of grAl thin films, we measure microwave resonators with open-boundary conditions and test the theoretical predictions in two limits. For low frequencies, we use standard microwave reflection measurements in a low-loss environment. The measured low-frequency modes are in agreement with our dispersion relation model, and we observe self-Kerr coefficients within an order of magnitude from our calculation starting from the grAl microstructure. Using a high-frequency setup, we measure the plasma frequency of the film around 70 GHz, in agreement with the analytical prediction.

Single-molecule magnet behaviour in a tetranuclear DyIII complex formed from a novel tetrazine-centered hydrazone Schiff base ligand.

Two analogous tetranuclear lanthanide complexes have been synthesized with the general formula [Ln4(vht)4(MeOH)8](NO3)4·aMeOH·bH2O, where H2vht = (3,6-bis(vanillidenehydrazinyl)-1,2,4,5-tetrazine) and Ln = DyIII (1), GdIII (2). These complexes are characterized by several techniques; including single-crystal X-ray diffraction, SQUID magnetometry and single-crystal micro-SQUID hysteresis loop measurements. Elucidation of the crystal structure of the complexes shows that the lanthanide ions are bridged by a tetrazine ring, a rare bridging moiety for lanthanide ions. Magnetic studies reveal that both 1 and 2 exhibit weak ferromagnetic exchange interactions between Ln ions, and 1 displaying Single-Molecule Magnet (SMM) behaviour with a magnetisation reversal barrier of Ueff = 158 K (τ0 = 1.06 × 10-7 s).

Single-molecule devices with graphene electrodes.

Several technological issues have to be faced to realize devices working at the single molecule level. One of the main challenges consists of defining methods to fabricate electrodes to make contact with single molecules. Here, we report the realization of novel spintronic devices made of a TbPc2 single molecule embedded between two nanometer-separated graphene electrodes, obtained by feedback-controlled electroburning. We demonstrate that this approach allows the realisation of devices working at low temperature. With these, we were able to characterize the magnetic exchange coupling between the electronic spin of the Tb3+ magnetic core and the current passing through the molecular system in the Coulomb blockade regime, thus showing that the use of graphene is a promising way forward in addressing single molecules.

The dynamics of drug resistance in Plasmodium falciparum.

Drug resistance of Plasmodium falciparum is not a recent phenomenon, but it became a major problem when the parasite became resistant to chloroquine, the cheapest and initially the most effective antimalarial compound that could be used for treatment and suppression. In some areas this problem is compounded by resistance to the first line of alternative drugs, and rapid loss of sensitivity to the next line. The dynamics of drug resistance are regulated mainly by drug related selection pressure and intensity of malaria transmission. Mass drug administration in its various forms, and insufficient treatment are obviously the most important motors of selection.