Evidence of weak superconductivity at the room-temperature grown LaAlO₃/SrTiO₃ interface

The two-dimensional electron gas at the crystalline LaAlO3/SrTiO3 (c-LAO/STO) interface has sparked large interest due to its exotic properties, including an intriguing gate-tunable superconducting phase. While there is growing evidence of pronounced spatial inhomogeneity in the conductivity at STO-based interfaces, the consequences for superconductivity remain largely unknown. We study interfaces based on amorphous LAO top layers grown at room temperature (a-LAO/STO) and demonstrate a superconducting phase similar to c-LAO/STO, however, with a gate-tunable critical temperature of 460 mK. The dependence of the superconducting critical current on temperature, magnetic field, and back-gate-controlled doping is found to be consistently described by a model of a random array of Josephson-coupled superconducting domains

Demonstration of Universal Parametric Entangling Gates on a Multi-Qubit Lattice

We show that parametric coupling techniques can be used to generate selective entangling interactions for multi-qubit processors. By inducing coherent population exchange between adjacent qubits under frequency modulation, we implement a universal gateset for a linear array of four superconducting qubits. An average process fidelity of $\mathcal{F}=93\%$ is estimated for three two-qubit gates via quantum process tomography. We establish the suitability of these techniques for computation by preparing a four-qubit maximally entangled state and comparing the estimated state fidelity against the expected performance of the individual entangling gates. In addition, we prepare an eight-qubit register in all possible bitstring permutations and monitor the fidelity of a two-qubit gate across one pair of these qubits. Across all such permutations, an average fidelity of $\mathcal{F}=91.6\pm2.6\%$ is observed. These results thus offer a path to a scalable architecture with high selectivity and low crosstalk

Universal distance-scaling of nonradiative energy transfer to graphene

6 pags, 4 figsThe near-field interaction between fluorescent emitters and graphene exhibits rich physics associated with local dipole-induced electromagnetic fields that are strongly enhanced due to the unique properties of graphene. Here, we measure emitter lifetimes as a function of emitter-graphene distance d, and find agreement with a universal scaling law, governed by the fine-structure constant. The observed energy transfer rate is in agreement with a 1/d 4 dependence that is characteristic of two-dimensional lossy media. The emitter decay rate is enhanced 90 times (energy transfer efficiency of ∼99%) with respect to the decay in vacuum at distances d ≈ 5 nm. This high energy transfer rate is mainly due to the two-dimensionality and gapless character of the monatomic carbon layer. Graphene is thus shown to be an extraordinary energy sink, holding great potential for photodetection, energy harvesting, and nanophotonics. © 2013 American Chemical Society.This work has been supported in part by the Fundacicio Cellex Barcelona, the ERC Starting Grant 307806 (CarbonLight), the ERC Career integration Grant 294056 (GRANOP), the Spanish MICINN (MAT2010-14885 and Consolider Nano-Light.es), and the European Commission (FP7-ICT-2009-4-248909-LIMA and FP7-ICT-2009-4-248855-N4E). L.G. acknowledges financial support from Marie-Curie International Fellowship COFUND and ICFOnest program. K.J.T. acknowledges financial support from NWO Rubicon grant. G.E.D.K.P. acknowledges support from a Leonardo da Vinci subsidy

Universal Distance-Scaling of Nonradiative Energy Transfer to Graphene

The near-field interaction between fluorescent emitters and graphene exhibits rich physics associated with local dipole-induced electromagnetic fields that are strongly enhanced due to the unique properties of graphene. Here, we measure emitter lifetimes as a function of emitter-graphene distance <i>d</i>, and find agreement with a universal scaling law, governed by the fine-structure constant. The observed energy transfer rate is in agreement with a 1/<i>d</i>⁴ dependence that is characteristic of two-dimensional lossy media. The emitter decay rate is enhanced 90 times (energy transfer efficiency of <i>∼</i>99%) with respect to the decay in vacuum at distances <i>d ≈</i> 5 nm. This high energy transfer rate is mainly due to the two-dimensionality and gapless character of the monatomic carbon layer. Graphene is thus shown to be an extraordinary energy sink, holding great potential for photodetection, energy harvesting, and nanophotonics