Strongly correlated quantum systems give rise to many exotic physical phenomena, including high-temperature superconductivity. Simulating these systems on quantum computers may avoid the ...prohibitively high computational cost incurred in classical approaches. However, systematic errors and decoherence effects presented in current quantum devices make it difficult to achieve this. Here, we simulate the dynamics of the one-dimensional Fermi-Hubbard model using 16 qubits on a digital superconducting quantum processor. We observe separations in the spreading velocities of charge and spin densities in the highly excited regime, a regime that is beyond the conventional quasiparticle picture. To minimize systematic errors, we introduce an accurate gate calibration procedure that is fast enough to capture temporal drifts of the gate parameters. We also employ a sequence of error-mitigation techniques to reduce decoherence effects and residual systematic errors. These procedures allow us to simulate the time evolution of the model faithfully despite having over 600 two-qubit gates in our circuits. Our experiment charts a path to practical quantum simulation of strongly correlated phenomena using available quantum devices.
We demonstrate the application of the Google Sycamore superconducting qubit quantum processor to combinatorial optimization problems with the quantum approximate optimization algorithm (QAOA). Like ...past QAOA experiments, we study performance for problems defined on the (planar) connectivity graph of our hardware; however, we also apply the QAOA to the Sherrington-Kirkpatrick model and MaxCut, both high dimensional graph problems for which the QAOA requires significant compilation. Experimental scans of the QAOA energy landscape show good agreement with theory across even the largest instances studied (23 qubits) and we are able to perform variational optimization successfully. For problems defined on our hardware graph we obtain an approximation ratio that is independent of problem size and observe, for the first time, that performance increases with circuit depth. For problems requiring compilation, performance decreases with problem size but still provides an advantage over random guessing for circuits involving several thousand gates. This behavior highlights the challenge of using near-term quantum computers to optimize problems on graphs differing from hardware connectivity. As these graphs are more representative of real world instances, our results advocate for more emphasis on such problems in the developing tradition of using the QAOA as a holistic, device-level benchmark of quantum processors.
As the search continues for useful applications of noisy intermediate scale quantum devices, variational simulations of fermionic systems remain one of the most promising directions. Here, we perform ...a series of quantum simulations of chemistry the largest of which involved a dozen qubits, 78 two-qubit gates, and 114 one-qubit gates. We model the binding energy of \({\rm H}_6\), \({\rm H}_8\), \({\rm H}_{10}\) and \({\rm H}_{12}\) chains as well as the isomerization of diazene. We also demonstrate error-mitigation strategies based on \(N\)-representability which dramatically improve the effective fidelity of our experiments. Our parameterized ansatz circuits realize the Givens rotation approach to non-interacting fermion evolution, which we variationally optimize to prepare the Hartree-Fock wavefunction. This ubiquitous algorithmic primitive corresponds to a rotation of the orbital basis and is required by many proposals for correlated simulations of molecules and Hubbard models. Because non-interacting fermion evolutions are classically tractable to simulate, yet still generate highly entangled states over the computational basis, we use these experiments to benchmark the performance of our hardware while establishing a foundation for scaling up more complex correlated quantum simulations of chemistry.
Scalable quantum computing can become a reality with error correction, provided coherent qubits can be constructed in large arrays. The key premise is that physical errors can remain both small and ...sufficiently uncorrelated as devices scale, so that logical error rates can be exponentially suppressed. However, energetic impacts from cosmic rays and latent radioactivity violate both of these assumptions. An impinging particle ionizes the substrate, radiating high energy phonons that induce a burst of quasiparticles, destroying qubit coherence throughout the device. High-energy radiation has been identified as a source of error in pilot superconducting quantum devices, but lacking a measurement technique able to resolve a single event in detail, the effect on large scale algorithms and error correction in particular remains an open question. Elucidating the physics involved requires operating large numbers of qubits at the same rapid timescales as in error correction, exposing the event's evolution in time and spread in space. Here, we directly observe high-energy rays impacting a large-scale quantum processor. We introduce a rapid space and time-multiplexed measurement method and identify large bursts of quasiparticles that simultaneously and severely limit the energy coherence of all qubits, causing chip-wide failure. We track the events from their initial localised impact to high error rates across the chip. Our results provide direct insights into the scale and dynamics of these damaging error bursts in large-scale devices, and highlight the necessity of mitigation to enable quantum computing to scale.
Superconducting qubits are an attractive platform for quantum computing since they have demonstrated high-fidelity quantum gates and extensibility to modest system sizes. Nonetheless, an outstanding ...challenge is stabilizing their energy-relaxation times, which can fluctuate unpredictably in frequency and time. Here, we use qubits as spectral and temporal probes of individual two-level-system defects to provide direct evidence that they are responsible for the largest fluctuations. This research lays the foundation for stabilizing qubit performance through calibration, design, and fabrication.
This is an updated version of supplementary information to accompany "Quantum supremacy using a programmable superconducting processor", an article published in the October 24, 2019 issue of Nature. ...The main article is freely available at https://www.nature.com/articles/s41586-019-1666-5. Summary of changes since arXiv:1910.11333v1 (submitted 23 Oct 2019): added URL for qFlex source code; added Erratum section; added Figure S41 comparing statistical and total uncertainty for log and linear XEB; new References 1,65; miscellaneous updates for clarity and style consistency; miscellaneous typographical and formatting corrections.
Human lymphocytes from elderly and young donors were cultured with phytohemagglutinin. Cultures from two groups of aged donors, recruited respectively from our ambulatory clinic and a nursing home, ...incorporated less tritiated thymidine (3H-TdR) and secreted less interleukin-2 than did young donors. Furthermore, as determined for the first time by a radioligand binding receptor assay, the aged lymphoblasts possessed significantly fewer high affinity IL-2 receptors per cell. Despite a decrease in the number of high affinity receptor cells the dissociation constant (Kd) was comparable for the three groups. It was also shown that the amounts of soluble IL-2 receptors that were released into the supernatants by mitogen stimulated cells did not differ for the aged and young donors. These data suggest that defects in IL-2 production and high affinity IL-2 receptor generation may both be responsible for immune deficiency in the elderly.
Drell-Yan lepton pairs produced in the process $p\bar{p} → ℓ^+ ℓ^−$ + X through an intermediate γ∗/Z boson have an asymmetry in their angular distribution related to the spontaneous symmetry breaking ...of the electroweak force and the associated mixing of its neutral gauge bosons. The CDF and D0 experiments have measured the effective-leptonic electroweak mixing parameter $sin^2 θ^{lept}_{eff}$ using electron and muon pairs selected from the full Tevatron proton-antiproton data sets collected in 2001-2011, corresponding to 9–10 fb$ ^{−1}$ of integrated luminosity. The combination of these measurements yields the most precise result from hadron colliders, $sin^2 θ^{lept}_{eff}$ = 0.23148±0.00033. This result is consistent with, and approaches in precision, the best measurements from electron-positron colliders. The standard model inference of the on-shell electroweak mixing parameter $sin^2 θ_W$, or equivalently the W-boson mass M$_W$, using the zfitter software package yields $sin^2 θ_W$ = 0.22324±0.00033 or equivalently, M$_W$=80.367±0.017 GeV/c$^2$.
Blood glucose control during pregnancy Skyler, Jay S; O'Sullivan, Mary Jo; Robertson, Euan G ...
Diabetes care,
01/1980, Letnik:
3, Številka:
1
Journal Article
Recenzirano
Blood glucose control during pregnancy.
J S Skyler ,
M J O'Sullivan ,
E G Robertson ,
D L Skyler ,
K K Holsinger ,
I A Lasky ,
A G McLeod ,
G Burkett and
D H Mintz
Abstract
Pregnant diabetic women ...represent a unique category of patient in whom diabetic control is most desirable, since even minor
degrees of hyperglycemia have adverse effects on the conceptus. In 18 insulin-dependent pregnant diabetic women (White Class
B, N = 4; C, N = 5; D, N = 7; and R, N =2), we have utilized a therapeutic program consisting of intensive patient education,
a multiple-component insulin regimen (two to four injections daily), careful dietary control, and meticulous balancing of
food, activity, and insulin dosage, monitoring such balance with patient-determined blood glucose measurements four to seven
times daily using the Dextrostix/Eyetone system. Our goals for blood glucose management have been to attain fasting levels
of 60-90 mg/dl, preprandial levels less than 105 mg/dl, and postprandial levels less than 120 mg/dl, in the absence of significant
hypoglycemia. We have been able to attain these goals for most of the period of monitoring in the majority of these patients,
while in the others we have achieved marked improvement in diabetic control, although we did not consistently attain our goals.
Despite this, there was not infrequent neonatal morbidity, including a 33% frequency of macrosomia, an 11% frequency of significant
hypoglycemia, and a 22% frequency of congenital malformation. Nevertheless, all infants survived and are generally healthy,
whereas only 38% of 21 previous pregnancies in these same women have eventuated in living offspring. Thus, although further
refinement is clearly indicated, it appears that our approach has resulted in improved pregnancy outcome. Patient self-monitoring
of blood glucose is a procedure that is relatively simple, practical, acceptable to patients, and facilitates the attainment
of glycemic control.
