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Silicon Qubits: High Fidelity

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Silicon Qubits: High Fidelity research highlights FRUSTRATED ANTIFERROMAGNETS open up the possibility of experimentally the task, yet they impose limitations on Spin-liquid ground state studying this quantum state. DC the choice of materials and can negatively Science 350, 655–658 (2015) affect cell viability. Su-Hwan Kim et al. now NANOPOROUS GOLD show that scaffolds based on paper offer an Single crystals attractive alternative. By taking advantage Nature Commun. 6, 8841 (2015) of the capabilities of paper origami and of vapour-based thin-film coating methods, There is substantial interest in the the researchers coated tissue-like paper fabrication of porous Au due to its high forms with cell-encapsulating alginate catalytic activity. Khristosov et al. now hydrogels to make scaffolds with pre- demonstrate a new approach for the designed shapes and spatially arranged cell synthesis of micro-scale nanoporous Au patterns (through the use of pre-patterned particles devoid of grain boundaries. The moulds placed on top of the paper). They approach they adopt is one of depositing Au also show that a cylindrical hydrogel- and Ge at their eutectic composition on an laden paper scaffold bearing articular SiO2 substrate, followed by heating to above chondrocytes regenerated a trachea defect AAAS the eutectic temperature; the melt dewets in rabbits without the need to use sutures, the substrate, forming solid spheres with a and with no signs of tissue granulation Frustrated antiferromagnetic interactions nanoscale eutectic structure, which is frozen or significant narrowing of the airway occur in materials where, due to the by subsequent cooling. Ge is then etched four weeks after transplantation. PP lattice geometry, the atomic spins cannot away, yielding a single crystal of Au with simultaneously minimize the energies of nanoscale pores. The authors discern that VAN DER WAALS COMPLEXES their local interactions. For instance, if the the lack of grain boundaries is a result of the Tunable charge transfer spins are arranged in an equilateral triangle, timescale for crystallization of one micro- Nano Lett. http://doi.org/9pp (2015) two of them can be antiferromagnetically droplet being shorter than the average coupled, yet the third cannot be similarly timescale between two nucleation events. coupled to the other two simultaneously. Importantly, the single-crystal structure Et Et This situation is found in antiferromagnetic makes the particles more thermally – materials with kagome lattices. The stable — as compared to dealloyed samples e e– exact nature of the ground state of these containing grain boundaries — potentially materials — or minimum energy state, boosting the temperature at which they may achievable by cooling them down — has be utilized. JP CHEMICAL AMERICAN SOCIETY been under debate. Now, Mingxuan Fu and colleagues report experimental evidence TISSUE ENGINEERING The electrical properties of graphene based on nuclear magnetic resonance and Paper scaffolds are highly sensitive to the perturbation magnetic susceptibility characterization, Proc. Natl Acad. Sci. USA http://doi.org/9pr (2015) of carrier concentration that is induced showing that the ground state of the by the physisorption of molecules on its kagome antiferromagnet ZnCu3(OH)6Cl2 When designing tissue scaffolds for surface. Now, Manoharan Muruganathan is a disordered state — namley, a spin-1/2 regenerating tissues with complex and colleagues show that the van der Waals spin liquid — with a finite gap between this forms, established technologies such as interactions between graphene and CO2 and the excited states. These results clarify electrospinning and mould-casting are at a molecules adsorbed onto it can be tuned the fundamental issue of the ground state disadvantage. Three-dimensional printing by applying an external electric field. By of these frustrated antiferromagnets and approaches are evidently better suited to means of first-principle calculations and transport measurements, they demonstrate that the molecules behave as weak electron SILICON QUBITS acceptors when no voltage is applied to the High fidelity Nature Nanotech. http://doi.org/9pq (2015) substrate, and that such electron transfer increases under the effect of a positive voltage. In contrast, a negative voltage Bell states feature the maximally achievable degree of entanglement, a necessary resource reverses the charge-transfer direction, for the implementation of efficient quantum computation algorithms. In this kind of causing the CO2 molecules to behave system, the state of two distinct particles cannot be described as a product of the states as donors. This is because the external of its local constituents. John Bell in 1964 defined the upper limit for such correlations to electric field alters the internal dipole occur assuming classical properties — locality and realism; violation of Bell’s theorem is created in the graphene–CO2 complex therefore directly linked to quantum entanglement. Andrea Morello and co-workers now together with the bonding distance and demonstrate entanglement between two-level systems (qubits) in a silicon platform. the O–C–O angle in the molecule. The The researchers prepared a maximally entangled state using the electron and the nuclear researchers suggest that such effects spins of a single phosphorus atom as qubits; the two-spin initialization fidelity was shown may be useful for the realization of to reach 97%. Two-qubit state tomography used to map out the density matrix of the graphene-based gas sensors with improved entangled states revealed very high, near-unity fidelity of 96% when compared to the ideal molecule-recognition capabilities. LM states. This demonstration of high-level manipulation of silicon-based qubits constitutes an important step towards real-life quantum computing. MM Written by David Ciudad, Maria Maragkou, Luigi Martiradonna, Pep Pàmies and John Plummer. NATURE MATERIALS | VOL 15 | JANUARY 2016 | www.nature.com/naturematerials 3 © 2015 Macmillan Publishers Limited. All rights reserved.
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