Accurately computing the electronic properties of a quantum ring.

A promising approach to study condensed-matter systems is to simulate them on an engineered quantum platform1-4. However, the accuracy needed to outperform classical methods has not been achieved so far. Here, using 18 superconducting qubits, we provide an experimental blueprint for an accurate condensed-matter simulator and demonstrate how to investigate fundamental electronic properties. We benchmark the underlying method by reconstructing the single-particle band structure of a one-dimensional wire. We demonstrate nearly complete mitigation of decoherence and readout errors, and measure the energy eigenvalues of this wire with an error of approximately 0.01 rad, whereas typical energy scales are of the order of 1 rad. Insight into the fidelity of this algorithm is gained by highlighting the robust properties of a Fourier transform, including the ability to resolve eigenenergies with a statistical uncertainty of 10-4 rad. We also synthesize magnetic flux and disordered local potentials, which are two key tenets of a condensed-matter system. When sweeping the magnetic flux we observe avoided level crossings in the spectrum, providing a detailed fingerprint of the spatial distribution of local disorder. By combining these methods we reconstruct electronic properties of the eigenstates, observing persistent currents and a strong suppression of conductance with added disorder. Our work describes an accurate method for quantum simulation5,6 and paves the way to study new quantum materials with superconducting qubits.

Demonstrating a Continuous Set of Two-Qubit Gates for Near-Term Quantum Algorithms.

Quantum algorithms offer a dramatic speedup for computational problems in material science and chemistry. However, any near-term realizations of these algorithms will need to be optimized to fit within the finite resources offered by existing noisy hardware. Here, taking advantage of the adjustable coupling of gmon qubits, we demonstrate a continuous two-qubit gate set that can provide a threefold reduction in circuit depth as compared to a standard decomposition. We implement two gate families: an imaginary swap-like (iSWAP-like) gate to attain an arbitrary swap angle, θ, and a controlled-phase gate that generates an arbitrary conditional phase, ϕ. Using one of each of these gates, we can perform an arbitrary two-qubit gate within the excitation-preserving subspace allowing for a complete implementation of the so-called Fermionic simulation (fSim) gate set. We benchmark the fidelity of the iSWAP-like and controlled-phase gate families as well as 525 other fSim gates spread evenly across the entire fSim(θ,ϕ) parameter space, achieving a purity-limited average two-qubit Pauli error of 3.8×10^{-3} per fSim gate.

[Application of the method of continuous suture annuloplasty for mitral valve disease of dysplastic etiology].

Considerable mitral regurgitation of dysplastic etiology was corrected in 63 patients using the method of continuous suture annuloplasty. The operations were fulfilled by the access through median sternotomy, under conditions of extracorporeal circulation, blood isothermal cardioplegy. Immediate results show effectiveness of correction of mitral insufficiency and safety of using the method due to the absence of lethal outcomes, thromboembolic complications and the necessity of another surgical correction in the nearest postoperative period.

[Surgical treatment of chronic thrombo-embolic pulmonary hypertension with floating thrombi in the right heart ventricle].

A 31 years old male patient was admitted to a resuscitation unit with severe dyspnea (MMRC 4 grade). The patient had the dyspnea for 3 months.The diagnosis of chronic thrombo-embolic pulmonary hypertension with floating thrombi in the right heart ventricle was established. On the sixth day of admission after IVC filter insertion, the patient underwent thromboectomy with pulmonary endarterectomy. For an access to segmentary pulmonary arteries during operation SVC and the aorta had been cross-clamped. The duration of deep hypothermic (20 degrees C) circulatory arrest was 54 minutes. The patient was discharged in satisfactory condition on the 17th day. At the check-up at 3 months the dyspnea was absent and heart hemodynamic parameters had been normalized.

[An experience with cardiac transplantation with a single stage reduction of the left atrium cavity and correction of valvular disease].

The immediate and long-term results of cardiac transplantation with a reduction of the left atrium and correction of valvular diseases were performed on 4 patients with atriomegalia and associated valvular disease of the heart. There were no cases of hospital lethality. Within 7 days after operation the patients had a tendency to reducing the mean value of the left atrium. Within 38 months the tendency to normalization of the sizes, volumes and ejection fraction of the left atrium persisted. Cardiac autotransplantation is an effective method of a single stage reduction of the left atrium and correction of valvular diseases.

Realizing topologically ordered states on a quantum processor.

The discovery of topological order has revised the understanding of quantum matter and provided the theoretical foundation for many quantum error­correcting codes. Realizing topologically ordered states has proven to be challenging in both condensed matter and synthetic quantum systems. We prepared the ground state of the toric code Hamiltonian using an efficient quantum circuit on a superconducting quantum processor. We measured a topological entanglement entropy near the expected value of ­ln2 and simulated anyon interferometry to extract the braiding statistics of the emergent excitations. Furthermore, we investigated key aspects of the surface code, including logical state injection and the decay of the nonlocal order parameter. Our results demonstrate the potential for quantum processors to provide insights into topological quantum matter and quantum error correction.

[Analysis of direct results of mitral valve annuloplasty].

In the present-day cardiosurgery there is no doubt that in case of possible plastic operation on the mitral valve the latter must be preserved. In the current literature there are no investigations which could convincingly prove advantages of any single group of techniques of constriction of the fibrous ring when performing mitral reconstructions. The aim of the work was to compare the direct results of reconstructive operations on the mitral valve with the using of three different means of constriction of the fibrous ring. It was found that all the three types of plasty of the mitral valve fibrous ring gave good direct results. Nevertheless an analysis of long-term results is necessary for the assessment of effectiveness of mitral reconstructions in the long-term postoperative period.

A blueprint for demonstrating quantum supremacy with superconducting qubits.

A key step toward demonstrating a quantum system that can address difficult problems in physics and chemistry will be performing a computation beyond the capabilities of any classical computer, thus achieving so-called quantum supremacy. In this study, we used nine superconducting qubits to demonstrate a promising path toward quantum supremacy. By individually tuning the qubit parameters, we were able to generate thousands of distinct Hamiltonian evolutions and probe the output probabilities. The measured probabilities obey a universal distribution, consistent with uniformly sampling the full Hilbert space. As the number of qubits increases, the system continues to explore the exponentially growing number of states. Extending these results to a system of 50 qubits has the potential to address scientific questions that are beyond the capabilities of any classical computer.

[Prosthesis of mitral valve in mesenchimal dysplasia: anatomo-morphological aspects and technical specificities].

Pathomorphological aspects of acquired mitral defects of the heart caused by manifestations of mesenchimal dysplasia were studied in 100 patients. Special attention is given to important features of surgical strategy when performing mitral valve prosthesis in such patients unlike similar procedures for mitral defects of another etiology.

[Immunoregulating effect of prostaglandins on the course of chronic lympholeukemia]. / Immunoreguliruiushchee vliianie prostaglandinov na techenie khronicheskogo limfoleikoza.

A study was made of the effect of exogenous prostaglandins E1, E2 and E2 alpha on the proliferative response of lymphocytes in blast transformation with PHA according to the changes in permeability for 3H-thymidine, 3H-thymidine incorporation into DNA, 3H-uridine into RNA and 3H-leucine into protein in 7 patients with stable and in 17 patients with progressive B-chronic lymphoid leukemia (B-CLL). The progression of B-CLL was marked by the lack of the regulating effect of PG on lymphocytes. In stable lymphoid leukemia, an inhibitory action of PG on lymphocyte proliferation could be seen. The characteristics of the lymphocyte responses in patients with B-CLL were employed for individual prediction of the disease course.

[Individual prognosis of chronic B-lymphoid leukemia course]. / Individual'noe prognozirovanie techeniia khronicheskogo B-limfoleikoza.

The characteristics of T- and B-lymphocyte content in chronic B-lymphoid leukemia (B-ChLL) patients with progressing and stable variants of the disease course, and the possibilities of their use for the individual prognosis of the course were studied. A total of 28 patients with stable and 35 patients with progressing variants of B-ChLL were investigated. T-(total and active) and B-lymphocytes were assayed in the spontaneous rosette-formation test. The individual prognosing of stable and progressing variants of B-ChLL course is possible basing on integral evaluation of total and active T-lymphocytes and B-lymphocytes with receptors to mouse red blood cells in two-dimensional parameter systems with counting the summary prognostic coefficient.

Spin-liquid phase in a spin-1/2 quantum magnet on the kagome lattice.

We study a model of hard-core bosons with short-range repulsive interactions at half filling on the kagome lattice. Using quantum Monte Carlo numerics, we find that this model shows a continuous superfluid-insulator quantum phase transition, with exponents z=1 and nu approximately 0.67(5). The insulator, I*, exhibits short-ranged density and bond correlations, topological order, and exponentially decaying spatial vison correlations, all of which point to a Z2 fractionalized phase. We estimate the vison gap in I* from the temperature dependence of the energy. Our results, together with the equivalence between hard-core bosons and S=1/2 spins, provide compelling evidence for a spin-liquid phase in an easy-axis spin-1/2 model with no special conservation laws.

Hard-core bosons on the kagome lattice: valence-bond solids and their quantum melting.

Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities rho=1/3 and rho=2/3. These solids exhibit an only partial ordering of the bosonic density, allowing for local resonances on a subset of hexagons of the kagome lattice. We provide evidence for a weakly first-order phase transition at the quantum melting point between these solid phases and the superfluid.

Why spin ice obeys the ice rules.

The low-temperature entropy of the spin ice compounds, such as and , is well described by the nearest-neighbor antiferromagnetic Ising model on the pyrochlore lattice, i.e., by the "ice rules." This is surprising since the dominant coupling between the spins is their long ranged dipole interaction. We show that this phenomenon can be understood rather elegantly: one can construct a model dipole interaction, by adding terms of shorter range, which yields precisely the same ground states, and hence entropy, as the nearest-neighbor interaction. A treatment of the small difference between the model and true dipole interactions reproduces the numerical work by Gingras et al. in detail. We are also led to a more general concept of projective equivalence between interactions.

Dipolar spin correlations in classical pyrochlore magnets.

We study spin correlations for the highly frustrated classical pyrochlore lattice antiferromagnets with O(N) symmetry in the limit T-->0. We conjecture that a local constraint obeyed by the extensively degenerate ground states dictates a dipolar form for the asymptotic spin correlations, at all N not equal 2 for which the system is paramagnetic down to T=0. We verify this conjecture in the cases N=1 and N=3 by simulations and to all orders in the 1/N expansion about the solvable N=infinity limit. Remarkably, the N=infinity formulas are an excellent fit, at all distances, to the correlators at N=3 and even at N=1. Thus we obtain a simple analytical expression also for the correlations of the equivalent models of spin ice and cubic water ice, Ic.