Geometric phase, associated with holonomy transformation in quantum state space, is an important quantum-mechanical effect. Besides fundamental interest, this effect has practical applications, among which geometric quantum computation is a paradigm, where quantum logic operations are realized through geometric phase manipulation that has some intrinsic noise-resilient advantages and may enable simplified implementation of multi-qubit gates compared to the dynamical approach. Here we report observation of a continuous-variable geometric phase and demonstrate a quantum gate protocol based on this phase in a superconducting circuit, where five qubits are controllably coupled to a resonator. Our geometric approach allows for one-step implementation of n-qubit controlled-phase gates, which represents a remarkable advantage compared to gate decomposition methods, where the number of required steps dramatically increases with n. Following this approach, we realize these gates with n up to 4, verifying the high efficiency of this geometric manipulation for quantum computation.

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Current-voltage characteristics, conduction mechanisms, and resistive switching properties are investigated in Al/Pr0.7Ca0.3MnO3 (PCMO)/Pt junctions. The junction resistance exhibits an irreversible increase from 2 to 90 MΩ in the forming process, the first several repeated bias sweeps. In contrast to the PCMO junctions involving inert top electrode (TE), the active Al-TE-based junctions show very large junction resistance and opposite cycling directions. It is found that the junction resistance sequence is qualitatively consistent with the standard Gibbs energies ΔG0 for the formation of corresponding TE oxides, rather than the Schottky barrier heights. Current-voltage fits indicate that the conduction processes in high and low resistance states are controlled by Poole–Frenkel emission and space-charge-limited conduction, respectively. The junctions show asymmetric switching thresholds with the minimal switching voltages are +1 V at the positive and −4 V at the negative side. Resistance retention tests indicate that the low resistance state is unstable and it gradually relaxes to higher resistance values. All the properties are discussed by the oxidation/reduction reaction at the Al/PCMO interface.

An efficient method that utilizes simple techniques, easy operation, and low-cost production to create flexible graphene-based materials is a worthy practical challenge. A rapid strategy for preparing flexible, functional graphene oxide (GO) is introduced using GO-ethanol dispersion filtration. The filtration process is highly efficient and drying time is significantly reduced by employing ethanol as solvent, due to the fact that ethanol is a volatile liquid. Freestanding GO papers can be harvested with ultralarge size (700 cm 2), color variety, and writable characteristics. After reduction, N-doped graphene (NDG) papers still maintain good foldability with improved electric conductivity and porous structure. When used as an electrode for a supercapacitor, the flexible NDG paper device demonstrates good electrochemical performance even with size expansion and extreme double folding. Moreover, this NDG paper capacitor device shows a good electrosorption performance for capacitive deionization of sulfate and chromate in groundwater system. These flexible GO and NDG papers promise potential to facilitate the production of graphene-based materials for practical applications in energy and environmental related fields.

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Current–voltage (I–V) characteristics are investigated in a low-initial-resistance Ag/Pr0.7Ca0.3MnO3/Pt sandwich structure. It is found that the junction can show stable low and high resistance states in ±0.3 V voltage sweeping cycles. The set and reset voltage values are, respectively, +0.1 V and −0.2 V, which are very low as compared with those reported previously. Furthermore, the I–V curves in both resistance states exhibit rather linear behaviour, without any signature of metal/insulator interface effects. This implies that the Schottky interface mechanism might not be an indispensable factor for the colossal electroresistance effect. The origin of low switching voltages is attributed to the reduced effective distance for electric field action due to the sufficient oxygen content of the PCMO layer. The underlying physics is discussed in terms of the filament network model together with the field-induced oxygen vacancy motion model.

Micro-patterning is considered to be a promising way to analyze phase-separated manganites. We investigate resistance in micro-patterned La0.325Pr0.3Ca0.375MnO3 wires with width of 10 μm, which is comparable to the phase separation scale in this material. A reentrant of insulating state at the metal—insulator temperature Tp is observed and a giant resistance change of over 90% driven by electric field is achieved by suppression of this insulating state. This resistance change is mostly reversible. The I—V characteristics are measured in order to analyze the origin of the giant electroresistance and two possible explanations are proposed.

Metal/insulator/metal structures composed of active Al top electrodes (TEs) and oxygen-deficient Pr0.7Ca0.3MnO3 (PCMO) insulator layers are prepared on platinized silicon substrates. The junction resistance exhibits an obvious negative differential resistance region in the first bias sweep and an irreversible increase from 2 to 100 MΩ in repeated ±4 V sweeps. The pulse duration needed to fully switch the junctions is found to be on the order of milliseconds. When 100–500 µs negative pulses are used, the junctions show an incomplete switch to the low resistance state (LRS) which exhibits fluctuating resistances. The fluctuation in the LRS is suppressed and the high-to-low resistance ratio increases gradually when the negative pulse duration is increased from 100 to 500 µs. For relaxed junctions, pulse switching experiments reveal that the LRS undergoes a dynamically stable process at the beginning and then reaches a lower and metastable resistance value. Resistance retention tests also indicate that the high resistance state is very stable, while the metastable LRS gradually relaxes to higher resistance values. The experimental results are discussed with the formation and dissociation of an interfacial AlOx layer at the interface between Al TEs and PCMO layers.