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Although sleep appears to be broadly conserved in animals, the physiological functions of sleep remain unclear. In this study, we sought to identify a physiological defect common to a diverse group of short-sleeping Drosophila mutants, which might provide insight into the function and regulation of sleep. We found that these short-sleeping mutants share a common phenotype of sensitivity to acute oxidative stress, exhibiting shorter survival times than controls. We further showed that increasing sleep in wild-type flies using genetic or pharmacological approaches increases survival after oxidative challenge. Moreover, reducing oxidative stress in the neurons of wild-type flies by overexpression of antioxidant genes reduces the amount of sleep. Together, these results support the hypothesis that a key function of sleep is to defend against oxidative stress and also point to a reciprocal role for reactive oxygen species (ROS) in neurons in the regulation of sleep.

Understanding freshwater fluxes at continental scales will help us better predict hydrologic response and manage our terrestrial water resources. The partitioning of evapotranspiration into bare soil evaporation and plant transpiration remains a key uncertainty in the terrestrial water balance. We used integrated hydrologic simulations that couple vegetation and land-energy processes with surface and subsurface hydrology to study transpiration partitioning at the continental scale. Both latent heat flux and partitioning are connected to water table depth, and including lateral groundwater flow in the model increases transpiration partitioning from 47 ± 13 to 62 ± 12%. This suggests that lateral groundwater flow, which is generally simplified or excluded in Earth system models, may provide a missing link for reconciling observations and global models of terrestrial water fluxes.

A warmer climate increases evaporative demand. However, response to warming depends on water availability. Existing earth system models represent soil moisture but simplify groundwater connections, a primary control on soil moisture. Here we apply an integrated surface-groundwater hydrologic model to evaluate the sensitivity of shallow groundwater to warming across the majority of the US. We show that as warming shifts the balance between water supply and demand, shallow groundwater storage can buffer plant water stress; but only where shallow groundwater connections are present, and not indefinitely. As warming persists, storage can be depleted and connections lost. Similarly, in the arid western US warming does not result in significant groundwater changes because this area is already largely water limited. The direct response of shallow groundwater storage to warming demonstrates the strong and early effect that low to moderate warming may have on groundwater storage and evapotranspiration. New hydrological simulations show for the first time how sensitive groundwater and surface water connections are to systematic warming across the continental United States. The authors here show a clear reduction in subsurface water storage under a warming climate and intensified aridification of north America.

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Three-qubit solid-state entanglement realized Quantum entanglement, in which the states of two or more particles are inextricably linked, is a key requirement for quantum computation. In superconducting devices, two-qubit entangled states have been used to implement simple quantum algorithms. The availability of three-qubit states, which can be entangled in two fundamentally different ways (the GHZ and W states), would be a significant advance because they should make it possible to perform error correction and infer scalability to the higher numbers of qubits needed for a practical quantum-information-processing device. Two groups now report the generation of three-qubit entanglement. John Martinis and colleagues create and measure both GHZ and W-type states. Leonardo DiCarlo and colleagues generate the GHZ state and demonstrate the first step of basic quantum error correction by encoding a logical qubit into a manifold of GHZ-like states using a repetition code. Quantum entanglement is a key resource for technologies such as quantum communication and computation. A major question for solid-state quantum information processing is whether an engineered system can display the three-qubit entanglement necessary for quantum error correction. A positive answer to this question is now provided. A circuit quantum electrodynamics device has been used to demonstrate deterministic production of three-qubit entangled states and the first step of basic quantum error correction. Traditionally, quantum entanglement has been central to foundational discussions of quantum mechanics. The measurement of correlations between entangled particles can have results at odds with classical behaviour. These discrepancies grow exponentially with the number of entangled particles 1 . With the ample experimental 2 , 3 , 4 confirmation of quantum mechanical predictions, entanglement has evolved from a philosophical conundrum into a key resource for technologies such as quantum communication and computation 5 . Although entanglement in superconducting circuits has been limited so far to two qubits 6 , 7 , 8 , 9 , the extension of entanglement to three, eight and ten qubits has been achieved among spins 10 , ions 11 and photons 12 , respectively. A key question for solid-state quantum information processing is whether an engineered system could display the multi-qubit entanglement necessary for quantum error correction, which starts with tripartite entanglement. Here, using a circuit quantum electrodynamics architecture 13 , 14 , we demonstrate deterministic production of three-qubit Greenberger–Horne–Zeilinger (GHZ) states 15 with fidelity of 88 per cent, measured with quantum state tomography. Several entanglement witnesses detect genuine three-qubit entanglement by violating biseparable bounds by 830 ± 80 per cent. We demonstrate the first step of basic quantum error correction, namely the encoding of a logical qubit into a manifold of GHZ-like states using a repetition code. The integration of this encoding with decoding and error-correcting steps in a feedback loop will be the next step for quantum computing with integrated circuits.

A controlled-controlled NOT, or Toffoli, gate is used to develop a fast, high-fidelity, three-qubit error correction protocol with the potential to correct arbitrary single-qubit errors. Quantum computing on the right track Efforts to harness the power of quantum computers are complicated by the fact that they are more prone to errors than classical computers. Such errors can be detected and corrected without affecting computational capability by using quantum error-correcting codes, the simplest of which are three-qubit codes. This paper reports the implementation of three-qubit quantum error correction using superconducting circuits. Phase- and bit-flip errors are corrected with high fidelity using a Toffoli gate, a logic gate that makes universal reversible classical computation possible. The work serves to establish the conceptual components of a more complex device that could correct arbitrary single-qubit errors. Quantum computers could be used to solve certain problems exponentially faster than classical computers, but are challenging to build because of their increased susceptibility to errors. However, it is possible to detect and correct errors without destroying coherence, by using quantum error correcting codes 1 . The simplest of these are three-quantum-bit (three-qubit) codes, which map a one-qubit state to an entangled three-qubit state; they can correct any single phase-flip or bit-flip error on one of the three qubits, depending on the code used 2 . Here we demonstrate such phase- and bit-flip error correcting codes in a superconducting circuit. We encode a quantum state 3 , 4 , induce errors on the qubits and decode the error syndrome—a quantum state indicating which error has occurred—by reversing the encoding process. This syndrome is then used as the input to a three-qubit gate that corrects the primary qubit if it was flipped. As the code can recover from a single error on any qubit, the fidelity of this process should decrease only quadratically with error probability. We implement the correcting three-qubit gate (known as a conditional-conditional NOT, or Toffoli, gate) in 63 nanoseconds, using an interaction with the third excited state of a single qubit. We find 85 ± 1 per cent fidelity to the expected classical action of this gate, and 78 ± 1 per cent fidelity to the ideal quantum process matrix. Using this gate, we perform a single pass of both quantum bit- and phase-flip error correction and demonstrate the predicted first-order insensitivity to errors. Concatenation of these two codes in a nine-qubit device would correct arbitrary single-qubit errors. In combination with recent advances in superconducting qubit coherence times 5 , 6 , this could lead to scalable quantum technology.