The accuracy of logical operations on quantum bits (qubits) must be improved for quantum computers to outperform classical ones in useful tasks. One method to achieve this is quantum error correction ...(QEC), which prevents noise in the underlying system from causing logical errors. This approach derives from the reasonable assumption that noise is local, that is, it does not act in a coordinated way on different parts of the physical system. Therefore, if a logical qubit is encoded non-locally, we can-for a limited time-detect and correct noise-induced evolution before it corrupts the encoded information
. In 2001, Gottesman, Kitaev and Preskill (GKP) proposed a hardware-efficient instance of such a non-local qubit: a superposition of position eigenstates that forms grid states of a single oscillator
. However, the implementation of measurements that reveal this noise-induced evolution of the oscillator while preserving the encoded information
has proved to be experimentally challenging, and the only realization reported so far relied on post-selection
, which is incompatible with QEC. Here we experimentally prepare square and hexagonal GKP code states through a feedback protocol that incorporates non-destructive measurements that are implemented with a superconducting microwave cavity having the role of the oscillator. We demonstrate QEC of an encoded qubit with suppression of all logical errors, in quantitative agreement with a theoretical estimate based on the measured imperfections of the experiment. Our protocol is applicable to other continuous-variable systems and, in contrast to previous implementations of QEC
, can mitigate all logical errors generated by a wide variety of noise processes and facilitate fault-tolerant quantum computation.
Fault-tolerant detection of a quantum error Rosenblum, S; Reinhold, P; Mirrahimi, M ...
Science (American Association for the Advancement of Science),
07/2018, Letnik:
361, Številka:
6399
Journal Article
Recenzirano
Odprti dostop
A critical component of any quantum error-correcting scheme is detection of errors by using an ancilla system. However, errors occurring in the ancilla can propagate onto the logical qubit, ...irreversibly corrupting the encoded information. We demonstrate a fault-tolerant error-detection scheme that suppresses spreading of ancilla errors by a factor of 5, while maintaining the assignment fidelity. The same method is used to prevent propagation of ancilla excitations, increasing the logical qubit dephasing time by an order of magnitude. Our approach is hardware-efficient, as it uses a single multilevel transmon ancilla and a cavity-encoded logical qubit, whose interaction is engineered in situ by using an off-resonant sideband drive. The results demonstrate that hardware-efficient approaches that exploit system-specific error models can yield advances toward fault-tolerant quantum computation.
Large-scale quantum information processing networks will most probably require the entanglement of distant systems that do not interact directly. This can be done by performing entangling gates ...between standing information carriers, used as memories or local computational resources, and flying ones, acting as quantum buses. We report the deterministic entanglement of two remote transmon qubits by Raman stimulated emission and absorption of a traveling photon wave packet. We achieve a Bell state fidelity of 73%, well explained by losses in the transmission line and decoherence of each qubit.
Entangling gates between qubits are a crucial component for performing algorithms in quantum computers. However, any quantum algorithm must ultimately operate on error-protected logical qubits ...encoded in high-dimensional systems. Typically, logical qubits are encoded in multiple two-level systems, but entangling gates operating on such qubits are highly complex and have not yet been demonstrated. Here we realize a controlled NOT (CNOT) gate between two multiphoton qubits in two microwave cavities. In this approach, we encode a qubit in the high-dimensional space of a single cavity mode, rather than in multiple two-level systems. We couple two such encoded qubits together through a transmon, which is driven by an RF pump to apply the gate within 190 ns. This is two orders of magnitude shorter than the decoherence time of the transmon, enabling a high-fidelity gate operation. These results are an important step towards universal algorithms on error-corrected logical qubits.
Aim
To determine whether the low C‐peptide levels (< 50 pmol/l) produced by the pancreas for decades after onset of Type 1 diabetes have clinical significance.
Methods
We evaluated fasting C‐peptide ...levels, duration of disease and age of onset in a large cross‐sectional series (n = 1272) of people with Type 1 diabetes. We then expanded the scope of the study to include the relationship between C‐peptide and HbA1c control (n = 1273), as well as diabetic complications (n = 324) and presence of hypoglycaemia (n = 323). The full range of C‐peptide levels was also compared with 1,5‐Anhydroglucitol, a glucose responsive marker.
Results
C‐peptide levels declined for decades after diagnosis, and the rate of decline was significantly related to age of onset (P < 0.0001), after adjusting for disease duration. C‐peptide levels > 10 pmol/l were associated with protection from complications (e.g. nephropathy, neuropathy, foot ulcers and retinopathy; P = 0.03). Low C‐peptide levels were associated with poor metabolic control measured by HbA1c (P < 0.0001). Severe hypoglycaemia was associated with the lowest C‐peptide levels compared with mild (P = 0.049) or moderate (P = 0.04) hypoglycaemia. All levels of measurable C‐peptide were responsive to acute fluctuations in blood glucose levels as assessed by 1,5‐Anhydroglucitol (P < 0.0001).
Conclusions
Low C‐peptide levels have clinical significance and appear helpful in characterizing groups at‐risk for faster C‐peptide decline, complications, poorer metabolic control and severe hypoglycaemia. Low C‐peptide levels may be a biomarker for characterizing at‐risk patients with Type 1 diabetes.
What's new?
We report the measurement of small amounts of residual insulin secretion, via an ultrasensitive C‐peptide assay, that identifies and stratifies people with Type 1 diabetes who are at risk of or have protection from complications and hypoglycaemia.
Measurement of low levels of C‐peptide may clinically identify at‐risk patients.
The data suggest a new therapeutic strategy of maintaining low C‐peptide levels, even in advanced disease, to avoid or prevent complications, improve HbA1c and lessen severe hypoglycaemia.
Manipulating the state of a logical quantum bit (qubit) usually comes at the expense of exposing it to decoherence. Fault-tolerant quantum computing tackles this problem by manipulating quantum ...information within a stable manifold of a larger Hilbert space, whose symmetries restrict the number of independent errors. The remaining errors do not affect the quantum computation and are correctable after the fact. Here we implement the autonomous stabilization of an encoding manifold spanned by Schrödinger cat states in a superconducting cavity. We show Zeno-driven coherent oscillations between these states analogous to the Rabi rotation of a qubit protected against phase flips. Such gates are compatible with quantum error correction and hence are crucial for fault-tolerant logical qubits.
A Molecular History of the Amyloidoses Buxbaum, Joel N.; Linke, Reinhold P.
Journal of molecular biology,
08/2012, Letnik:
421, Številka:
2-3
Journal Article
Recenzirano
The molecular investigation of the amyloidoses began in the mid-19th century with the observation of areas in human tissues obtained at autopsy that were homogeneous and eosinophilic with ...conventional stains but became blue when exposed to mixtures of iodine and sulfuric acid. The foci corresponded to regions formerly identified as “waxy” or lardaceous. Subsequent identification of the characteristic staining of the same tissues with metachromatic dyes such as crystal violet or with the cotton dye Congo red (particularly under polarized light) and thioflavins allowed the pathological classification of those tissues as belonging to a set of disorders known as the amyloidoses. Not unexpectedly, progress has reflected evolving technology and parallel advances in all fields of biological science. Investigation using contemporary methods has expanded our notions of amyloid proteins from being simply agents or manifestations of systemic, largely extracellular diseases to include “protein-only infection,” the concept that “normal” functional amyloids might exist in eukaryotes and prokaryotes and that aggregatability may be an intrinsic structural price to be paid for some functional protein domains. We now distinguish between the amyloidoses, that is, diseases caused by the deposition of amyloid fibrils and amyloid proteins (i.e., purified or recombinant proteins that form amyloid fibrils in vitro), which may or may not be associated with disease in vivo.
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Acute-phase proteins (APPs) are an evolutionarily conserved family of proteins produced mainly in the liver in response to infection and inflammation. Despite vast pro- and antiinflammatory ...properties ascribed to individual APPs, their collective function during infections remains poorly defined. Using a mouse model of polymicrobial sepsis, we show that abrogation of APP production by hepatocyte-specific gp130 deletion, the signaling receptor shared by IL-6 family cytokines, strongly increased mortality despite normal bacterial clearance. Hepatic gp130 signaling through STAT3 was required to control systemic inflammation. Notably, hepatic gp130-STAT3 activation was also essential for mobilization and tissue accumulation of myeloid-derived suppressor cells (MDSCs), a cell population mainly known for antiinflammatory properties in cancer. MDSCs were critical to regulate innate inflammation, and their adoptive transfer efficiently protected gp130-deficient mice from sepsis-associated mortality. The hepatic APPs serum amyloid A and Cxcl1/KC cooperatively promoted MDSC mobilization, accumulation, and survival, and reversed dysregulated inflammation and restored survival of gp130-deficient mice. Thus, gp130-dependent communication between the liver and MDSCs through APPs controls inflammatory responses during infection.
•Anomalous mean stress effects are observed in Ti-6Al-4V at high R ratios.•A critical soft-hard-soft grain combination is associated with crack initiation.•The percentage of grains being plasticized ...is lower at higher R ratios.•Multiple families of slip systems are activated at higher R ratios.•Pyramidal slip is significant in a macrozone with c-axes parallel to the loading axis.
In engineering practice, mean stress corrections are employed to assess the fatigue performance of a material or structure; albeit this is problematic for Ti-6Al-4V, which experiences anomalous behavior at high R ratios. To address this problem, high cycle fatigue analyses were performed on two Ti-6Al-4V specimens with equiaxed alpha microstructures at a high R ratio. In one specimen, two micro-textured regions (MTRs) having their c-axes near parallel and perpendicular to the loading direction were identified. High-resolution digital image correlation (HR-DIC) was performed in the MTRs to study grain-level strain localization. In the other specimen, DIC was performed on a larger area and crack initiation was observed in a random-textured region. To accompany the experiments, crystal plasticity finite element simulations were performed to investigate the mechanistic aspects of crack initiation, and the relative activity of different families of slip systems as a function of R ratio. A critical soft-hard-soft grain combination was associated with crack initiation indicating possible dwell effect at high R ratios, which could be attributed to the high-applied mean stress and high creep sensitivity of Ti-6Al-4V at room temperature. Further, simulations indicated more heterogeneous deformation, specifically the activation of multiple families of slip systems with fewer grains being plasticized, at higher R ratios. Such behavior is exacerbated within MTRs, especially the MTR composed of grains with their c-axes near parallel to the loading direction. These features of micro-plasticity make the high R ratio regime more vulnerable to fatigue damage accumulation and justify the anomalous mean stress behavior experienced by Ti-6Al-4V at high R ratios.
Every amyloid disease needs to be assessed for chemical composition of its amyloid because amyloid is pathogenetically diverse and each of the chemical amyloid types requires a different therapy. ...Basically four different approaches are being applied for typing of amyloid using immunohistochemistry, immunochemistry, mass spectrometry and chemistry. It is shown here how an easy immunohistochemical procedure has been developed over the years that can be used to classify specifically amyloid proteins for clinico-pathologic routine use. A larger number of tissues with chemically or immunochemically typed amyloids served as prototypes for developing a set of validated amyloid antibodies. These were examined for their performance to classify a larger number of tissues of patients submitted to us and other institutions allowing independent evaluation. The data reveal that out of 663 patients, including 15 different amyloid types, all 119 prototype Amyloids (100%) have been classified correctly and 97.9% of consecutive 581 unknown amyloid tissues submitted for typing to our laboratory of whom 37 became later prototypes. Twelve samples (2.1%) could not be classified. By using appropriate amyloid antibodies in a comparative manner, this procedure is accurate. It identifies the respective amyloid type and excludes simultaneously other amyloids. Its improved performance leads to an accurate amyloid diagnosis in most cases and provides a diagnostic marker which is independend of any other information for therapeutic considerations. These results can be obtained within a day in institutes competent in performing immunohistochemistry. This is the first report on immunhistochemical typing of amyloid providing detailed illustrations of the original results for training purposes. When the immunohistochemical method presented here was compared with mass spectrometry, a more recent method for amyloid typing, the advantages and failures of both methods became apparent in an international blinded comparison.
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