We present the first experimental results on a device with more than two superconducting qubits. The circuit consists of four three-junction flux qubits, with simultaneous ferro- and antiferromagnetic coupling implemented using shared Josephson junctions. Its response, which is dominated by the ground state, is characterized using low-frequency impedance measurement with a superconducting tank circuit coupled to the qubits. The results are found to be in excellent agreement with the quantum-mechanical predictions.

Development of fast highly-sensitive semiconductor gas sensors operating at room temperature, which would be compatible with semiconductor technology, remains a challenge for researchers. Here we present such sensor based on a nanoscale Pt–TiO2–Pt sandwich. The sensor consists of a thin (∼30nm) nanocrystalline TiO2 layer with ∼10nm grains, placed between the bottom Pt electrode layer and top Pt electrode shaped as a long narrow (width w down to 80nm) stripe. If we decrease w to ∼100nm and below, the sensor exposed to air with 1% H2 exhibits the increase of response (Rair/RH2) up to ∼107 and decrease of the reaction time to only a few seconds even at room temperature. The sensitivity increase is due to a nontrivial non-ohmic effect, a sudden decrease (by three orders of magnitude) of the electrical resistance with decreasing w for w∼100nm. This non-ohmic effect is explained as a consequence of two nanoscale-related effects: the hydrogen-diffusion-controlled spatially-inhomogeneous resistivity of the TiO2 layer, combined with onset of the hot-electron-temperature instability when the tiny grains are subjected to high electric field

Capacitorlike metal/metal oxide/metal structures are widely used as resistive switching cells and are utilized in resistive random access memories. Recently, it has been demonstrated that they also perform well as gas sensors. In this work, we have merged the gas sensing and resistive switching capabilities of the capacitorlike Pt/TiO₂/Pt structures to constitute a simple device which works as a gas-triggered thyristorlike switch and as a gas sensor with a built-in memory.