16 research outputs found
Experimental Hamiltonian identification for controlled two-level systems
We present a strategy to empirically determine the internal and control Hamiltonians for an unknown two-level system (black box) subject to various (piecewise constant) control fields when direct readout by measurement is limited to a single, fixed observable
Controlled phase gate for solid-state charge qubits
We describe a mechanism for realizing a controlled phase gate for solid-state
charge qubits. By augmenting the positionally defined qubit with an auxiliary
state, and changing the charge distribution in the three-dot system, we are
able to effectively switch the Coulombic interaction, effecting an entangling
gate. We consider two architectures, and numerically investigate their
robustness to gate noise.Comment: 14 pages, 11 figures, 2 tables, RevTeX
Quantum System Identification by Bayesian Analysis of Noisy Data: Beyond Hamiltonian Tomography
We consider how to characterize the dynamics of a quantum system from a
restricted set of initial states and measurements using Bayesian analysis.
Previous work has shown that Hamiltonian systems can be well estimated from
analysis of noisy data. Here we show how to generalize this approach to systems
with moderate dephasing in the eigenbasis of the Hamiltonian. We illustrate the
process for a range of three-level quantum systems. The results suggest that
the Bayesian estimation of the frequencies and dephasing rates is generally
highly accurate and the main source of errors are errors in the reconstructed
Hamiltonian basis.Comment: 6 pages, 3 figure
Physics-based mathematical models for quantum devices via experimental system identification
We consider the task of intrinsic control system identification for quantum
devices. The problem of experimental determination of subspace confinement is
considered, and simple general strategies for full Hamiltonian identification
and decoherence characterization of a controlled two-level system are
presented.Comment: 15 pages, 8 figures, published in proceedings of workshop on
Physics-based mathematical models of low-dimensional semi-conductor
nanostructures (18-23 November, 2007, Banff International Research Station,
Alberta, Canada
Physics-based mathematical models for quantum devices via experimental system identification
We consider the task of intrinsic control system identification for quantum
devices. The problem of experimental determination of subspace confinement is
considered, and simple general strategies for full Hamiltonian identification
and decoherence characterization of a controlled two-level system are
presented.Comment: 15 pages, 8 figures, published in proceedings of workshop on
Physics-based mathematical models of low-dimensional semi-conductor
nanostructures (18-23 November, 2007, Banff International Research Station,
Alberta, Canada
Physics-based mathematical models for quantum devices via experimental system identification
We consider the task of intrinsic control system identification for quantum
devices. The problem of experimental determination of subspace confinement is
considered, and simple general strategies for full Hamiltonian identification
and decoherence characterization of a controlled two-level system are
presented.Comment: 15 pages, 8 figures, published in proceedings of workshop on
Physics-based mathematical models of low-dimensional semi-conductor
nanostructures (18-23 November, 2007, Banff International Research Station,
Alberta, Canada
Cardiac xenotransplantation: Recent preclinical progress with 3-month median survival
ObjectivesTransplantation is limited by a lack of human organ donors. Organs derived from animals, most likely the pig, represent a potential solution to this problem. For the heart, 90-day median graft survival of life-supporting pig hearts transplanted to nonhuman primates has been considered a reasonable standard for entry into the clinical arena. Overcoming the immune barrier to successful cardiac xenotransplantation is most appropriately first explored with the non–life-supporting heterotopic model.MethodsWe performed a series of 7 heterotopic heart transplantations from CD46 transgenic pigs to baboons using a combination of therapeutic agents largely targeted at controlling the synthesis of anti-pig antibodies. Rituximab (anti-CD20) and Thymoglobulin (rabbit antithymocyte globulin [ATG]; SangStat Medical Corp, Fremont, Calif) were used as induction therapy. Baseline immunosuppression consisted of splenectomy, tacrolimus, sirolimus, steroids, and TPC (an anti-Gal antibody therapeutic). Rejection events were not treated.ResultsBy using Kaplan-Meier analysis, median graft survival was 96 days (range, 15–137 days; 95% confidence interval, 38–99 days). Only 2 grafts were lost as a result of rejection, as defined by cessation of graft palpation. There was no evidence of a consumptive coagulopathy, infectious complications were treatable, and no posttransplantation lymphoproliferative disorders occurred. No cellular infiltration was observed.ConclusionsThis study reports the longest median survival to date (96 days) of pig hearts transplanted heterotopically into baboons. Duplication of these results in the orthotopic life-supporting position could bring cardiac xenotransplantation to the threshold of clinical application
Robust Online Hamiltonian Learning
In this work we combine two distinct machine learning methodologies,
sequential Monte Carlo and Bayesian experimental design, and apply them to the
problem of inferring the dynamical parameters of a quantum system. We design
the algorithm with practicality in mind by including parameters that control
trade-offs between the requirements on computational and experimental
resources. The algorithm can be implemented online (during experimental data
collection), avoiding the need for storage and post-processing. Most
importantly, our algorithm is capable of learning Hamiltonian parameters even
when the parameters change from experiment-to-experiment, and also when
additional noise processes are present and unknown. The algorithm also
numerically estimates the Cramer-Rao lower bound, certifying its own
performance.Comment: 24 pages, 12 figures; to appear in New Journal of Physic
Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.
BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700