1,831 research outputs found
Hybrid Optimization Schemes for Quantum Control
Optimal control theory is a powerful tool for solving control problems in
quantum mechanics, ranging from the control of chemical reactions to the
implementation of gates in a quantum computer. Gradient-based optimization
methods are able to find high fidelity controls, but require considerable
numerical effort and often yield highly complex solutions. We propose here to
employ a two-stage optimization scheme to significantly speed up convergence
and achieve simpler controls. The control is initially parametrized using only
a few free parameters, such that optimization in this pruned search space can
be performed with a simplex method. The result, considered now simply as an
arbitrary function on a time grid, is the starting point for further
optimization with a gradient-based method that can quickly converge to high
fidelities. We illustrate the success of this hybrid technique by optimizing a
holonomic phasegate for two superconducting transmon qubits coupled with a
shared transmission line resonator, showing that a combination of Nelder-Mead
simplex and Krotov's method yields considerably better results than either one
of the two methods alone.Comment: 17 pages, 5 figures, 2 table
Charting the circuit QED design landscape using optimal control theory
With recent improvements in coherence times, superconducting transmon qubits
have become a promising platform for quantum computing. They can be flexibly
engineered over a wide range of parameters, but also require us to identify an
efficient operating regime. Using state-of-the-art quantum optimal control
techniques, we exhaustively explore the landscape for creation and removal of
entanglement over a wide range of design parameters. We identify an optimal
operating region outside of the usually considered strongly dispersive regime,
where multiple sources of entanglement interfere simultaneously, which we name
the quasi-dispersive straddling qutrits (QuaDiSQ) regime. At a chosen point in
this region, a universal gate set is realized by applying microwave fields for
gate durations of 50 ns, with errors approaching the limit of intrinsic
transmon coherence. Our systematic quantum optimal control approach is easily
adapted to explore the parameter landscape of other quantum technology
platforms.Comment: 13 pages, 5 figures, 2 pages supplementary, 1 supplementary figur
Robustness of high-fidelity Rydberg gates with single-site addressability
Controlled phase (CPHASE) gates can in principle be realized with trapped
neutral atoms by making use of the Rydberg blockade. Achieving the ultra-high
fidelities required for quantum computation with such Rydberg gates is however
compromised by experimental inaccuracies in pulse amplitudes and timings, as
well as by stray fields that cause fluctuations of the Rydberg levels. We
report here a comparative study of analytic and numerical pulse sequences for
the Rydberg CPHASE gate that specifically examines the robustness of the gate
fidelity with respect to such experimental perturbations. Analytical pulse
sequences of both simultaneous and stimulated Raman adiabatic passage (STIRAP)
are found to be at best moderately robust under these perturbations. In
contrast, optimal control theory is seen to allow generation of numerical
pulses that are inherently robust within a predefined tolerance window. The
resulting numerical pulse shapes display simple modulation patterns and their
spectra contain only one additional frequency beyond the basic resonant Rydberg
gate frequencies. Pulses of such low complexity should be experimentally
feasible, allowing gate fidelities of order 99.90 - 99.99% to be achievable
under realistic experimental conditions.Comment: 12 pages, 14 figure
Does DTC advertising affect physician prescribing habits?
Direct-to-consumer advertising (DTCA) is associated with both higher fidelity to minimum treatment recommendations for depression and higher prescribing levels of antidepressants for depression and adjustment disorder (strength of recommendation [SOR]: B, small randomized controlled trial [RCT]). DTCA is also associated with higher prescribing rates for osteoarthritis, allergies, and hyperlipidemia (SOR: C, time-series analyses). No changes in prescribing rates have been noted for hypertension and benign prostatic hyperplasia (SOR: C, time-series analyses). Physicians often accommodate requests for DTCA medications (SOR: C, 4 surveys). In some cases, they wouldn't have considered such prescriptions for other similar patients (SOR: C, 3 surveys)
Staphylococcus aureus proteins Sbi and Efb recruit human plasmin to degrade complement C3 and C3b
Upon host infection, the human pathogenic microbe Staphylococcus aureus (S. aureus) immediately faces innate immune reactions such as the activated complement system. Here, a novel innate immune evasion strategy of S. aureus is described. The staphylococcal proteins surface immunoglobulin-binding protein (Sbi) and extracellular fibrinogen-binding protein (Efb) bind C3/C3b simultaneously with plasminogen. Bound plasminogen is converted by bacterial activator staphylokinase or by host-specific urokinase-type plasminogen activator to plasmin, which in turn leads to degradation of complement C3 and C3b. Efb and to a lesser extend Sbi enhance plasmin cleavage of C3/C3b, an effect which is explained by a conformational change in C3/C3b induced by Sbi and Efb. Furthermore, bound plasmin also degrades C3a, which exerts anaphylatoxic and antimicrobial activities. Thus, S. aureus Sbi and Efb comprise platforms to recruit plasmin(ogen) together with C3 and its activation product C3b for efficient degradation of these complement components in the local microbial environment and to protect S. aureus from host innate immune reactions
Phosphocholine-Modified Lipooligosaccharides of Haemophilus influenzae Inhibit ATP-Induced IL-1beta Release by Pulmonary Epithelial Cells
Phosphocholine-modified bacterial cell wall components are virulence factors enabling immune evasion and permanent colonization of the mammalian host, by mechanisms that are poorly understood. Recently, we demonstrated that free phosphocholine (PC) and PC-modified lipooligosaccharides (PC-LOS) from Haemophilus influenzae, an opportunistic pathogen of the upper and lower airways, function as unconventional nicotinic agonists and efficiently inhibit the ATP-induced release of monocytic IL-1beta. We hypothesize that H. influenzae PC-LOS exert similar effects on pulmonary epithelial cells and on the complex lung tissue. The human lung carcinoma-derived epithelial cell lines A549 and Calu-3 were primed with lipopolysaccharide from Escherichia coli followed by stimulation with ATP in the presence or absence of PC or PC-LOS or LOS devoid of PC. The involvement of nicotinic acetylcholine receptors was tested using specific antagonists. We demonstrate that PC and PC-LOS efficiently inhibit ATP-mediated IL-1beta release by A549 and Calu-3 cells via nicotinic acetylcholine receptors containing subunits alpha7, alpha9, and/or alpha10. Primed precision-cut lung slices behaved similarly. We conclude that H. influenzae hijacked an endogenous anti-inflammatory cholinergic control mechanism of the lung to evade innate immune responses of the host. These findings may pave the way towards a host-centered antibiotic treatment of chronic airway infections with H. influenzae
Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters
We present chemodynamical links between the present-day Milky Way halo field
star population and Galactic globular clusters (GCs) using a dataset that
combines information from the space mission and the Sloan
Digital Sky Survey (SDSS-IV, DR14). Moreover, we incorporated a sample of halo
giant stars with a distinct chemical signature (strong CN bandheads) that
resembles the light-elements anomaly otherwise only seen in the second
generation of GC stellar populations. Using three different tagging techniques,
we could successfully establish unique associations between 151 extratidal
stars in the neighborhood of eight GCs. In addition, we traced the possible
origin of about of the sample of CN-strong giants to their potential
host clusters. Several of the involved GCs have been brought into connection
with the Gaia-Enceladus and Sequoia merger events. By establishing kinematic
and chemical connections between 17 CN-strong stars and their surrounding
fields, we could identify co-moving groups of stars at the same [Fe/H] with a
possible cluster origin. We found strong evidence that four CN-strong stars and
their associates are connected to the Sagittarius stream whilst their tightly
confined [Fe/H] may hint to a birth site in M 54. Finally, we provide tentative
estimates for the fraction of first-generation cluster stars among all stars
lost to the halo. In the immediate cluster vicinity, this value amounts to
while the associations in the halo field rather imply
. We speculate that -- if proven real by spectroscopic
follow-up -- the disparity between these numbers could indicate a major
contribution of low-mass clusters to the overall number of stars escaped to the
halo or, alternatively, point toward a strong mass loss from the first
generation during early cluster dissolution. [abridged]Comment: 20 pages (+9 pages of appendices), 39 figures, 4 tables, accepted for
publication in A&
Subthreshold Voltage Noise Due to Channel Fluctuations in Active Neuronal Membranes
Voltage-gated ion channels in neuronal membranes fluctuate randomly between different conformational states due to thermal agitation. Fluctuations between conducting and nonconducting states give rise to noisy membrane currents and subthreshold voltage fluctuations and may contribute to variability in spike timing. Here we study subthreshold voltage fluctuations due to active voltage-gated Na+ and K+ channels as predicted by two commonly used kinetic schemes: the Mainen et al. (1995) (MJHS) kinetic scheme, which has been used to model dendritic channels in cortical neurons, and the classical Hodgkin-Huxley (1952) (HH) kinetic scheme for the squid giant axon. We compute the magnitudes, amplitude distributions, and power spectral densities of the voltage noise in isopotential membrane patches predicted by these kinetic schemes. For both schemes, noise magnitudes increase rapidly with depolarization from rest. Noise is larger for smaller patch areas but is smaller for increased model temperatures. We contrast the results from Monte Carlo simulations of the stochastic nonlinear kinetic schemes with analytical, closed-form expressions derived using passive and quasi-active linear approximations to the kinetic schemes. For all subthreshold voltage ranges, the quasi-active linearized approximation is accurate within 8% and may thus be used in large-scale simulations of realistic neuronal geometries
Functional and Clinicopathologic Outcomes Using a Modified Vescica Ileale Padovana Technique
Objective: To evaluate the clinicopathologic and functional outcomes of a modified Vescica ileale Padovana (VIP) neobladder technique. Methods: Data for 160 patients at a single institution who underwent radical cystectomy and orthotopic VIP neoblad
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