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Undesired coupling to the surrounding environment destroys long-range correlations in quantum processors and hinders coherent evolution in the nominally available computational space. This noise is an outstanding challenge when leveraging the computation power of near-term quantum processors1. It has been shown that benchmarking random circuit sampling with cross-entropy benchmarking can provide an estimate of the effective size of the Hilbert space coherently available2–8. Nevertheless, quantum algorithms’ outputs can be trivialized by noise, making them susceptible to classical computation spoofing. Here, by implementing an algorithm for random circuit sampling, we demonstrate experimentally that two phase transitions are observable with cross-entropy benchmarking, which we explain theoretically with a statistical model. The first is a dynamical transition as a function of the number of cycles and is the continuation of the anti-concentration point in the noiseless case. The second is a quantum phase transition controlled by the error per cycle; to identify it analytically and experimentally, we create a weak-link model, which allows us to vary the strength of the noise versus coherent evolution. Furthermore, by presenting a random circuit sampling experiment in the weak-noise phase with 67 qubits at 32 cycles, we demonstrate that the computational cost of our experiment is beyond the capabilities of existing classical supercomputers. Our experimental and theoretical work establishes the existence of transitions to a stable, computationally complex phase that is reachable with current quantum processors.

An important measure of the development of quantum computing platforms has been the simulation of increasingly complex physical systems. Before fault-tolerant quantum computing, robust error-mitigation strategies were necessary to continue this growth. Here, we validate recently introduced error-mitigation strategies that exploit the expectation that the ideal output of a quantum algorithm would be a pure state. We consider the task of simulating electron systems in the seniority-zero subspace where all electrons are paired with their opposite spin. This affords a computational stepping stone to a fully correlated model. We compare the performance of error mitigations on the basis of doubling quantum resources in time or in space on up to 20 qubits of a superconducting qubit quantum processor. We observe a reduction of error by one to two orders of magnitude below less sophisticated techniques such as postselection. We study how the gain from error mitigation scales with the system size and observe a polynomial suppression of error with increased resources. Extrapolation of our results indicates that substantial hardware improvements will be required for classically intractable variational chemistry simulations.

The detection of individual quanta of light is important for quantum communication, fluorescence lifetime imaging, remote sensing and more. Due to their high detection efficiency, exceptional signal-to-noise ratio and fast recovery times, superconducting-nanowire single-photon detectors (SNSPDs) have become a critical component in these applications. However, the operation of conventional SNSPDs requires costly cryocoolers. Here we report the fabrication of two types of high-temperature superconducting nanowires. We observe linear scaling of the photon count rate on the radiation power at the telecommunications wavelength of 1.5 μm and thereby reveal single-photon operation. SNSPDs made from thin flakes of Bi2Sr2CaCu2O8+δexhibit a single-photon response up to 25 K, and for SNSPDs from La1.55Sr0.45CuO4/La2CuO4bilayer films, this response is observed up to 8 K. While the underlying detection mechanism is not fully understood yet, our work expands the family of materials for SNSPD technology beyond the liquid helium temperature limit and suggests that even higher operation temperatures may be reached using other high-temperature superconductors.

Background: Neuroendocrine tumors (NETs) of the diffuse neuroendocrine cell system often present a considerable diagnostic and therapeutic challenge. Methods: We have reviewed the literature on NET treatment between 1979 and 2008 (PubMed search: carcinoid or neuroendocrine tumor/tumour treatment or management), and summarized current therapeutic options and recommendations. Results: The majority of tumors are diagnosed at a stage that the only curative treatment, radical surgical intervention, is no longer an option. Biotherapy with somatostatin analogs is currently the most efficient treatment to achieve palliation. The interferon class of agents may have a role in selected individuals but substantial adverse events often limit their use. Conventional chemotherapy has minimal efficacy but may have some utility in undifferentiated or highly proliferating neuroendocrine carcinomas and pancreatic NETs. Hepatic metastases, depending on size, location and number, may be amenable to surgical resection, embolization or radio-frequency ablation. Peptide receptor targeted radiotherapy may lead to reduction in tumor size but in most circumstances has a tumor-stabilizing effect. A variety of antiangiogenesis and growth factor-targeted agents have been evaluated but to date the results have failed to meet expectations. Thus, long-acting somatostatin analogs remain the only effective pharmacotherapeutic option that improves symptomatology and quality of life with minimal adverse effects.

Abstract The characteristics of the neutron fields (spectrum, fluence) at four points of the GIR-2 reactor are measured. It is shown experimentally that the energy spectrum of leakage neutrons from the reactor core through an opening in a spherical converter, which consists of light elements and inside which the core is placed, becomes harder. This effect is due to the shift of the region in the core where the number density of fissions is high toward the lateral surface of the core as a result of the presence the converter, consisting of light elements, outside the core. On the basis of the results of these investigations, GIR-2 neutron fields are certified as reference standards for measurements.

Modal birefringence (the difference between the effective refractive indices of orthogonal polarisation modes) is one of the key parameters of anisotropic single-mode fibres, characterising their ability to preserve a linearly polarised state of input light. This parameter is commonly measured using short pieces of fibre, but such procedures are destructive and allow the birefringence to be determined only at the ends of long fibres. In this study, polarised light Brillouin reflectometry is used to assess birefringence uniformity throughout the length of an anisotropic fibre.

A method of fabricating porous powder Ti-Ni diffusion couples was developed, and the structure of the diffusion zone in these after isothermal annealing at 1073, 1173, and 1273 K studied. Microstructural analysis and microhardness measurements revealed that the width of the diffusion zone and the thickness of the intermetallic layers increased with increasing temperature. Mutual diffusion coefficients were calculated, and an explanation proposed for the more rapid intermetallic layer growth in porous powder than in solid diffusion couples above 1173 K. This was related to the presence of rapid diffusion paths (surfaces, grain boundaries) which persisted at high temperatures in the porous powder diffusion couples, while those in solid couples (point and line defects) were eliminated when the temperature was raised.

Porous titanium nickelide exhibiting the shape “memory” effect has been produced from pressed titanium and nickel (carbonyl and electrolytic) powder mixtures of equiatomic composition by high-temperature vacuum sintering resulting in interdiffusion of its components without the formation of a liquid phase. Use of a carbonyl rather than an electrolytic powder in the starting mixture enables sintered TiNi of better physicomechanical properties to be obtained. Sintered TiNi can find practical application not only as a semifinished product in the manufacture of nonporous parts by hot working but also for the production of parts whose thermomechanical recovery characteristics are their key service properties.

A procedure has been developed for the direct observation of the sintering of uncompacted metal powders in the IMASH-1 high-temperature installation. The mechanism by which metallic contacts between tinned bronze granules are initiated and propagated during heating has been established. It was found that, with increasing rate of heating, the temperature of metal contact formation and granule surface melting decreases, as a result of which it is possible to produce filters with a relatively high tin content of the surface layers of granules.

Conclusions 1.The reduction of thin oxide films can be effectively studied by the method of high-temperature microscopy. From the change in the surface coloring of compacts from oxidized powder, the effect of temperature during heating in a hydrogen atmosphere at a residual pressure of 1–10-1 mm Hg on the thickness of the particle oxide film was established.2.With the method of high-temperature microscopy, it is possible to examine the kinetics of variation in the surface microstructure of compacts during their sintering. The first signs of a change in the relief of the surface microstructure of heated compacts from the series A and B powders were noted at temperatures 150–200° in excess of the reduction temperatures of the starting powders.3.After sintering, compacts from the series A copper powder attained a higher density than compacts from the series B powder when the compacting pressure did not exceed 7 tons/cm2.4.The highest density after sintering was achieved in specimens compacted at a pressure of 5 tons/cm{su2}. This was the optimum compacting pressure for the production of compacts from the series A and B powders.

1.Using the technique of high-temperature metallography, a study was made of the sintering behavior of reduced copper powders. It was established that the temperature range corresponding to the formation and growth of metallic contacts between powder particles depends on the reduction temperature of the powder.2.On the basis of experimental data on contact growth, a quantitative evaluation is made of the coefficients of surface self-diffusion and energy of activation. It is shown that the effective coefficient of surface self-diffusion for a copper powder reduced at a low temperature is an order of magnitude greater than that for a copper powder reduced at a high temperature.3.It was found that the effective value of activation energy for the process of contact growth between reduced copper powder particles does not remain constant as a function of sintering temperature. With rise in sintering temperature, the effective value of activation energy increases as a result of an improvement in the structural equilibrium attained in the surface layers of particles in such powders.

1.Fine waste of rimmed steel and cast iron can be used as a raw material in the manufacture of cheap fine iron powder suitable for the cermet industry.2.The microstructural investigation of this fine waste as well as the chemical analysis showed with an adequate accuracy its condition and proved that it is suitable for the intended purpose; they also made possible the selection of a suitable method for processing this waste to iron powder which can be used as a raw material by the cermet industry.3.It has been shown that in principle it is possible to obtain iron powder: a) from fine waste of rimmed steel by the method used in the reduction of rolling scale and b) from fine waste of liquid cast iron using the hydromechanical and iron ore methods normally employed in processing cast iron chips. Special research is needed to develop the commercial processes for producing iron powder from this waste.

Abstract: An experimental genetically engineered plague vaccine strain LAG1 has been constructed, e ensuring 27 times better protection (due to capsular antigen) than the maternal culture of commercial live antiplague vaccine (EV strain of the Research Institute of Epidemiology and Hygiene).