Abstract
Quantum annealing provides a way of solving optimization problems by encoding them as Ising spin models which are implemented using physical qubits. The solution of the optimization problem ...then corresponds to the ground state of the system. Quantum tunneling is harnessed to enable the system to move to the ground state in a potentially high non-convex energy landscape. A major difficulty in encoding optimization problems in physical quantum annealing devices is the fact that many real world optimization problems require interactions of higher connectivity, as well as multi-body terms beyond the limitations of the physical hardware. In this work we address the question of how to implement multi-body interactions using hardware which natively only provides two-body interactions. The main result is an efficient circuit design of such multi-body terms using superconducting flux qubits in which effective
N
-body interactions are implemented using
N
ancilla qubits and only two inductive couplers. It is then shown how this circuit can be used as the unit cell of a scalable architecture by applying it to a recently proposed embedding technique for constructing an architecture of logical qubits with arbitrary connectivity using physical qubits which have nearest-neighbor four-body interactions. It is further shown that this design is robust to non-linear effects in the coupling loops, as well as mismatches in some of the circuit parameters.
Bleeding and transfusion after percutaneous coronary intervention (PCI) are known predictors of mortality. Transradial arterial access reduces bleeding and transfusion related to femoral access ...complications, although its association with mortality is unknown.
To determine the association of arterial access site (radial or femoral) with transfusion and mortality in unselected PCIs.
By data linkage of three prospectively collated provincial registries, 38,872 procedures in 32,822 patients in British Columbia were analysed. The association between access site, transfusion and outcomes was assessed by logistic regression, propensity score matching and probit regression.
30-Day and 1-year mortality.
1134 (3.5%) patients had at least one blood transfusion. Transfused patients had a significantly increased 30-day and 1-year mortality, adjusted odds ratio (95% CI) 4.01 (3.08 to 5.22) and 3.58 (2.94 to 4.36), respectively. By probit regression the absolute increase in risk of death at 1 year associated with receiving a transfusion was 6.78%. The number needed to treat was 14.74 (prevention of 15 transfusions required to "avoid" one death). Radial access halved the transfusion rate. After adjustment for all variables, radial access was associated with a significant reduction in 30-day and 1-year mortality, odds ratio = 0.71 (95% CI 0.61 to 0.82) and 0.83 (0.71 to 0.98), respectively (all p<0.001).
In a registry of all comers to PCI, transradial access was associated with a halving of the transfusion rate and a reduction in 30-day and 1-year mortality.
Circularly polarized light is incident on a nanostructured chiral meta‐surface. In the nanostructured unit cells whose chirality matches that of light, superchiral light is forming and strong optical ...second harmonic generation can be observed.
We demonstrate a direct mapping of max k-SAT problems (and weighted max k-SAT) to a Chimera graph, which is the non-planar hardware graph of the devices built by D-Wave Systems Inc. We further show ...that this mapping can be used to map a similar class of maximum satisfiability problems where the clauses are replaced by parity checks over potentially large numbers of bits. The latter is of specific interest for applications in decoding for communication. We discuss an example in which the decoding of a turbo code, which has been demonstrated to perform near the Shannon limit, can be mapped to a Chimera graph. The weighted max k-SAT problem is the most general class of satisfiability problems, so our result effectively demonstrates how any satisfiability problem may be directly mapped to a Chimera graph. Our methods faithfully reproduce the low energy spectrum of the target problems, so therefore may also be used for maximum entropy inference.
Glaciers and ice streams flowing over sediment beds commonly have a layer of ice‐rich debris adhered to their base, known as a “frozen fringe,” but its impact on basal friction is unknown. We ...simulated basal slip over granular beds with a cryogenic ring shear device while ice infiltrated the bed to grow a fringe, and measured the frictional response under different effective stresses and slip speeds. Frictional resistance increased with increasing slip speed until it plateaued at the frictional strength of the till, closely resembling the regularized Coulomb slip law associated with clean ice over deformable beds. We hypothesize that this arises from deformation in a previously unidentified zone of weakly frozen sediments at the fringe's base, which is highly sensitive to temperature and stress gradients. We show how a rheologic model for ice‐rich debris coupled with the thermomechanics of fringe growth can account for the regularized Coulomb behavior.
Plain Language Summary
Many glaciers move by sliding over sediment beds. As the glacier flows downslope, ice can infiltrate the underlying sediments, forming a layer of ice‐rich debris attached at the glacier's base. We investigated how this frozen fringe impacts glacier motion by simulating glacier slip in a cold‐room facility with a specialized ring shear device. We recreated glacier conditions, sliding ice over granular beds to form the fringe, and then assessed how frictional resistance at the slip interface varied under different stresses and ice speeds. We found that frozen fringe influences the relationship between ice speed and frictional resistance, known as the “slip law.” As ice speed increased, basal friction increased to a threshold that matches the strength of the ice‐free sediment bed—mirroring the “regularized Coulomb slip law” inferred for clean ice over soft beds. We attribute this behavior to deformation in a weakly frozen zone at the base of the frozen fringe and show how this behavior can be incorporated into existing parameterizations of glacier slip.
Key Points
Ring shear experiments show frozen fringe alters basal slip dynamics for soft‐bedded glaciers
Deformation in a zone of weakly frozen sediments within the fringe leads to a regularized Coulomb slip response
Improvements in the resolution of sea-floor mapping techniques have revealed extremely regular, sub-metre-scale ridge landforms produced by the tidal flexure of ice-shelf grounding lines as they ...retreated very rapidly (i.e. at rates of several kilometres per year). Guided by such novel sea-floor observations from Thwaites Glacier, West Antarctica, we present three mathematical models for the formation of these corrugation ridges at a tidally migrating grounding line (that is retreating at a constant rate), where each ridge is formed by either constant till flux to the grounding line, till extrusion from the grounding line, or the resuspension and transport of grains from the grounding-zone bed. We find that both till extrusion (squeezing out till like toothpaste as the ice sheet re-settles on the sea floor) and resuspension and transport of material can qualitatively reproduce regular, delicate ridges at a retreating grounding line, as described by sea-floor observations. By considering the known properties of subglacial sediments, we agree with existing schematic models that the most likely mechanism for ridge formation is till extrusion at each low-tide position, essentially preserving an imprint of the ice-sheet grounding line as it retreated. However, when realistic (shallow) bed slopes are used in the simulations, ridges start to overprint one another, suggesting that, to preserve the regular ridges that have been observed, grounding line retreat rates (driven by dynamic thinning?) may be even higher than previously thought.
Coupling between tunable broadband modes of an array of plasmonic metamolecules and a vibrational mode of carbonyl bond of poly(methyl methacrylate) is shown experimentally to produce a Fano ...resonance, which can be tuned in situ by varying the polarization of incident light. The interaction between the plasmon modes and the molecular resonance is investigated using both rigorous electromagnetic calculations and a quantum mechanical model describing the quantum interference between a discrete state and two continua. The predictions of the quantum mechanical model are in good agreement with the experimental data and provide an intuitive interpretation, at the quantum level, of the plasmon-molecule coupling.
A significant challenge in quantum annealing is to map a real-world problem onto a hardware graph of limited connectivity. When the problem graph is not a subgraph of the hardware graph, one might ...employ minor embedding in which each logical qubit is mapped to a tree of physical qubits. Pairwise interactions between physical qubits in the tree are set to be ferromagnetic with some coupling strength
F
<
0
. Here we address the theoretical question of what the best value
F
should be in order to achieve unbroken trees in the pre-quantum-processing. The sum of |
F
| for each logical qubit is defined as minor embedding energy, and the best value
F
is obtained when the minor embedding energy is minimized. We also show that our new analytical lower bound on |
F
| is a tighter bound than that previously derived by Choi (Quantum Inf Process 7:193–209, 2008). In contrast to Choi’s work, our new method depends more delicately on minor embedding parameters, which leads to a higher computational cost.
We investigate different processes for optimizing the formation of Ohmic contacts to InAs nanowires. The nanowires are grown via molecular beam epitaxy without the use of metal catalysts. Metallic ...contacts are attached to the nanowires by using an electron beam lithography process. Before deposition of the contacts, the InAs nanowires are treated either by wet etching in an ammonium polysulfide (NH(4))(2)S(x) solution or by an argon milling process in order to remove a surface oxide layer. Two-point electrical measurements show that the resistance of the ammonium polysulfide-treated nanowires is two orders of magnitude lower than that of the untreated nanowires. The nanowires that are treated by the argon milling process show a resistance which is more than an order of magnitude lower than that of those treated with ammonium polysulfide. Four-point measurements allow us to extract an upper bound of 1.4 × 10(-7) Ω cm(2) for the contact resistivity of metallic contacts on nanowires treated by the argon milling process.
This study examines the hydrogen peroxide concentrations measured near four models of hydrogen peroxide sterilizers, from two manufacturers, monitored in seven hospitals across the U.S. and Canada ...over several years. The results showed that the majority of sterilizers do not emit hazardous levels of hydrogen peroxide and none of them exceeded the OSHA PEL of 1 ppm (8-hr time-weighted average (TWA)), however several of the sterilizers exceeded 3 ppm, the short-term exposure limit in two states: Washington and Hawaii. One hospital found brief concentrations of 25-40 ppm hydrogen peroxide from 4 hydrogen peroxide sterilizers each time they opened the sterilizer at the end of its cycle. Although not exceeding the OSHA PEL, these exposures are of concern since this concentration is roughly half the NIOSH IDLH of 75 ppm, and operators in a busy hospital environment may receive these exposures multiple times a day.
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