61 results on '"Doherty, P. C."'
Search Results
2. Scalable noise characterisation of syndrome extraction circuits with averaged circuit eigenvalue sampling
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Hockings, Evan T., Doherty, Andrew C., and Harper, Robin
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Quantum Physics - Abstract
Characterising the performance of noisy quantum circuits is central to the production of prototype quantum computers and can enable improved quantum error correction that exploits noise biases identified in a quantum device. We describe an implementation of averaged circuit eigenvalue sampling (ACES), a general framework for the scalable noise characterisation of quantum circuits. ACES is capable of simultaneously estimating the Pauli error probabilities of all gates in a Clifford circuit, and captures averaged spatial correlations between gates implemented simultaneously in the circuit. By rigorously analysing the performance of ACES experiments, we derive a figure of merit for their expected performance, allowing us to optimise ACES experimental designs and improve the precision to which we estimate noise given fixed experimental resources. Since the syndrome extraction circuits of quantum error correcting codes are representative components of a fault-tolerant architecture, we demonstrate the scalability and performance of our ACES protocol through circuit-level numerical simulations of the entire noise characterisation procedure for the syndrome extraction circuit of a distance 25 surface code with over 1000 qubits. Our results indicate that detailed noise characterisation methods are scalable to near-term quantum devices. We release our code in the form of the Julia package AveragedCircuitEigenvalueSampling.jl., Comment: 15 pages + 15 page appendix, 22 figures, comments welcome
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- 2024
3. Logical Gates and Read-Out of Superconducting Gottesman-Kitaev-Preskill Qubits
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Shaw, Mackenzie H., Doherty, Andrew C., and Grimsmo, Arne L.
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Quantum Physics - Abstract
The Gottesman-Kitaev-Preskill (GKP) code is an exciting route to fault-tolerant quantum computing since Gaussian resources and GKP Pauli-eigenstate preparation are sufficient to achieve universal quantum computing. In this work, we provide a practical proposal to perform Clifford gates and state read-out in GKP codes implemented with active error correction in superconducting circuits. We present a method of performing Clifford circuits without physically implementing any single-qubit gates, reducing the potential for them to spread errors in the system. In superconducting circuits, all the required two-qubit gates can be implemented with a single piece of hardware. We analyze the error-spreading properties of GKP Clifford gates and describe how a modification in the decoder following the implementation of each gate can reduce the gate infidelity by multiple orders of magnitude. Moreover, we develop a simple analytical technique to estimate the effect of loss and dephasing on GKP codes that matches well with numerics. Finally, we consider the effect of homodyne measurement inefficiencies on logical state read-out and present a scheme that implements a measurement with a $0.1\%$ error rate in $630$ ns assuming an efficiency of just~$75\%$., Comment: 41 pages, 19 figures, corrected typos
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- 2024
4. Concatenating Binomial Codes with the Planar Code
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Soule, Juliette, Doherty, Andrew C., and Grimsmo, Arne L.
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Quantum Physics - Abstract
Rotation symmetric bosonic codes are an attractive encoding for qubits into oscillator degrees of freedom, particularly in superconducting qubit experiments. While these codes can tolerate considerable loss and dephasing, they will need to be combined with higher level codes to achieve large-scale devices. We investigate concatenating these codes with the planar code in a measurement-based scheme for fault-tolerant quantum computation. We focus on binomial codes as the base level encoding, and estimate break-even points for such encodings under loss for various types of measurement protocol. These codes are more resistant to photon loss errors, but require both higher mean photon numbers and higher phase resolution for gate operations and measurements. We find that it is necessary to implement adaptive phase measurements, maximum likelihood quantum state inference, and weighted minimum weight decoding to obtain good performance for a planar code using binomial code qubits.
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- 2023
5. Universal flux-based control of a $\pi$-SQUID
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Staples, J. Wilson, Smith, Thomas B., and Doherty, Andrew C.
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Quantum Physics - Abstract
We describe a protocol for the universal control of non-ideal $\pi$-periodic superconducting qubits. Our proposal relies on a $\pi$-SQUID: a superconducting loop formed by two $\pi$-periodic circuit elements, with an external magnetic flux threading the circuit. The system exhibits an extensive sweet spot around half-flux where residual $2\pi$-periodic Cooper pair tunneling is highly suppressed. We demonstrate that universal single-qubit operations can be realised by tuning the flux adiabatically and diabatically within this broad sweet spot. We also assess how residual $2\pi$-periodicity in $\pi$-SQUIDs impacts holonomic phase gates., Comment: 8 pages, 4 figures
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- 2023
6. No Strings Attached: Boundaries and Defects in the Cubic Code
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Aitchison, Cory T., Bulmash, Daniel, Dua, Arpit, Doherty, Andrew C., and Williamson, Dominic J.
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Quantum Physics ,Condensed Matter - Strongly Correlated Electrons - Abstract
Haah's cubic code is the prototypical type-II fracton topological order. It instantiates the no string-like operator property that underlies the favorable scaling of its code distance and logical energy barrier. Previously, the cubic code was only explored in translation-invariant systems on infinite and periodic lattices. In these settings, the code distance scales superlinearly with the linear system size, while the number of logical qubits within the degenerate ground space exhibits a complicated functional dependence that undergoes large fluctuations within a linear envelope. Here, we extend the cubic code to systems with open boundary conditions and crystal lattice defects. We characterize the condensation of topological excitations in the vicinity of these boundaries and defects, finding that their inclusion can introduce local string-like operators and enhance the mobility of otherwise fractonic excitations. Despite this, we use these boundaries and defects to define new encodings where the number of logical qubits scales linearly without fluctuations, and the code distance scales superlinearly, with the linear system size. These include a subsystem encoding with open boundary conditions and a subspace encoding using lattice defects., Comment: 27 pages, 28 figures
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- 2023
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7. Edge Theories for Anyon Condensation Phase Transitions
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Long, David M. and Doherty, Andrew C.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
The algebraic tools used to study topological phases of matter are not clearly suited to studying processes in which the bulk energy gap closes, such as phase transitions. We describe an elementary two edge thought experiment which reveals the effect of an anyon condensation phase transition on the robust edge properties of a sample, bypassing a limitation of the algebraic description. In particular, the two edge construction allows some edge degrees of freedom to be tracked through the transition, despite the bulk gap closing. The two edge model demonstrates that bulk anyon condensation induces symmetry breaking in the edge model. Further, the construction recovers the expected result that the number of chiral current carrying modes at the edge cannot change through anyon condensation. We illustrate the construction through detailed analysis of anyon condensation transitions in an achiral phase, the toric code, and in chiral phases, the Kitaev spin liquids., Comment: 26 pages, 9 figures; (v2) additional references; (v3) explained relation to previous results, minor clarifications; (v4) additional references
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- 2023
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8. Extreme Weather Disruptions and Emergency Preparedness Among Older Adults in Ohio: An Eight-County Assessment
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Rao, Smitha, Doherty, Fiona C., Traver, Anthony, Sheldon, Marisa, Sakulich, Emma, and Dabelko-Schoeny, Holly
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- 2024
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9. Gottesman-Kitaev-Preskill state preparation using periodic driving
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Kolesnikow, Xanda C., Bomantara, Raditya Weda, Doherty, Andrew C., and Grimsmo, Arne L.
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Quantum Physics - Abstract
The Gottesman-Kitaev-Preskill (GKP) code may be used to overcome noise in continuous variable quantum systems. However, preparing GKP states remains experimentally challenging. We propose a method for preparing GKP states by engineering a time-periodic Hamiltonian whose Floquet states are GKP states. This Hamiltonian may be realized in a superconducting circuit comprising a SQUID shunted by a superinductor and a capacitor, with a characteristic impedance twice the resistance quantum. The GKP Floquet states can be prepared by adiabatically tuning the frequency of the external magnetic flux drive. We predict that highly squeezed $>11.9$ dB ($10.8$ dB) GKP magic states can be prepared on a microsecond timescale, given a quality factor of $10^6$ ($10^5$) and flux noise at typical rates., Comment: Includes main text and supplementary material
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- 2023
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10. Stabilizer subsystem decompositions for single- and multi-mode Gottesman-Kitaev-Preskill codes
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Shaw, Mackenzie H., Doherty, Andrew C., and Grimsmo, Arne L.
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Quantum Physics - Abstract
The Gottesman-Kitaev-Preskill (GKP) error correcting code encodes a finite dimensional logical space in one or more bosonic modes, and has recently been demonstrated in trapped ions and superconducting microwave cavities. In this work we introduce a new subsystem decomposition for GKP codes that we call the stabilizer subsystem decomposition, analogous to the usual approach to quantum stabilizer codes. The decomposition has the defining property that a partial trace over the non-logical stabilizer subsystem is equivalent to an ideal decoding of the logical state. We describe how to decompose arbitrary states across the subsystem decomposition using a set of transformations that move between the decompositions of different GKP codes. Besides providing a convenient theoretical view on GKP codes, such a decomposition is also of practical use. We use the stabilizer subsystem decomposition to efficiently simulate noise acting on single-mode GKP codes, and in contrast to more conventional Fock basis simulations, we are able to to consider essentially arbitrarily large photon numbers for realistic noise channels such as loss and dephasing., Comment: 34 pages, 12 figures, 1 table; referee feedback implemented
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- 2022
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11. The origins of SARS-CoV-2: A critical review
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Holmes, Edward C, Goldstein, Stephen A, Rasmussen, Angela L, Robertson, David L, Crits-Christoph, Alexander, Wertheim, Joel O, Anthony, Simon J, Barclay, Wendy S, Boni, Maciej F, Doherty, Peter C, Farrar, Jeremy, Geoghegan, Jemma L, Jiang, Xiaowei, Leibowitz, Julian L, Neil, Stuart JD, Skern, Tim, Weiss, Susan R, Worobey, Michael, Andersen, Kristian G, Garry, Robert F, and Rambaut, Andrew
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Biological Sciences ,Bioinformatics and Computational Biology ,Biomedical and Clinical Sciences ,Infectious Diseases ,Pneumonia ,Coronaviruses ,Pneumonia & Influenza ,Emerging Infectious Diseases ,Lung ,Good Health and Well Being ,Animals ,Biological Evolution ,COVID-19 ,Humans ,Laboratories ,SARS-CoV-2 ,Zoonoses ,evolution ,origins ,zoonosis ,Medical and Health Sciences ,Developmental Biology ,Biological sciences ,Biomedical and clinical sciences - Abstract
Since the first reports of a novel severe acute respiratory syndrome (SARS)-like coronavirus in December 2019 in Wuhan, China, there has been intense interest in understanding how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in the human population. Recent debate has coalesced around two competing ideas: a "laboratory escape" scenario and zoonotic emergence. Here, we critically review the current scientific evidence that may help clarify the origin of SARS-CoV-2.
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- 2021
12. Development and Validation of ICD-10-CM-based Algorithms for Date of Last Menstrual Period, Pregnancy Outcomes, and Infant Outcomes
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Chomistek, Andrea K., Phiri, Kelesitse, Doherty, Michael C., Calderbank, Jenna F., Chiuve, Stephanie E., McIlroy, Brenda Hinman, Snabes, Michael C., Enger, Cheryl, and Seeger, John D.
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- 2023
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13. Testing Generalised Uncertainty Principles through Quantum Noise
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Girdhar, Parth and Doherty, Andrew C.
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Quantum Physics ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory - Abstract
Motivated by several approaches to quantum gravity, there is a considerable literature on generalised uncertainty principles particularly through modification of the canonical position-momentum commutation relations. Some of these modified relations are also consistent with general principles that may be supposed of any physical theory. Such modified commutators have significant observable consequences. Here we study the noisy behaviour of an optomechanical system assuming a certain commonly studied modified commutator. From recent observations of radiation pressure noise in tabletop optomechanical experiments as well as the position noise spectrum of Advanced LIGO we derive bounds on the modified commutator. We find how such experiments can be adjusted to provide significant improvements in such bounds, potentially surpassing those from sub-atomic measurements., Comment: 16+11 pages, 5 figures. Journal version
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- 2020
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14. Solving quantum trajectories for systems with linear Heisenberg-picture dynamics and Gaussian measurement noise
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Warszawski, P., Wiseman, H. M., and Doherty, A. C.
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Quantum Physics - Abstract
We study solutions to the quantum trajectory evolution of $N$-mode open quantum systems possessing a time-independent Hamiltonian, linear Heisenberg-picture dynamics, and Gaussian measurement noise. In terms of the mode annihilation and creation operators, a system will have linear Heisenberg-picture dynamics under two conditions. First, the Hamiltonian must be quadratic. Second, the Lindblad operators describing the coupling to the environment (including those corresponding to the measurement) must be linear. In cases where we can solve the $2N$-degree polynomials that arise in our calculations, we provide an analytical solution for initial states that are arbitrary (i.e. they are not required to have Gaussian Wigner functions). The solution takes the form of an evolution operator, with the measurement-result dependence captured in $2N$ stochastic integrals over these classical random signals. The solutions also allow the POVM, which generates the probabilities of obtaining measurement outcomes, to be determined. To illustrate our results, we solve some single-mode example systems, with the POVMs being of practical relevance to the inference of an initial state, via quantum state tomography. Our key tool is the representation of mixed states of quantum mechanical oscillators as state vectors rather than state matrices (albeit in a larger Hilbert space). Together with methods from Lie algebra, this allows a more straightforward manipulation of the exponential operators comprising the system evolution than is possible in the original Hilbert space., Comment: 34 pages, 1 figure, changed title
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- 2020
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15. Tomography of an optomechanical oscillator via parametrically amplified position measurement
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Warszawski, P., Szorkovszky, A., Bowen, W. P., and Doherty, A. C.
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Quantum Physics - Abstract
We propose a protocol for quantum state tomography of nonclassical states in optomechanical systems. Using a parametric drive, the procedure overcomes the challenges of weak optomechanical coupling, poor detection efficiency, and thermal noise to enable high efficiency homodyne measurement. Our analysis is based on the analytic description of the generalized measurement that is performed when optomechanical position measurement competes with thermal noise and a parametric drive. The proposed experimental procedure is numerically simulated in realistic parameter regimes, which allows us to show that tomographic reconstruction of otherwise unverifiable nonclassical states is made possible., Comment: 37 pages, 5 figures, comments welcome. Published version
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- 2018
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16. Fast spin exchange between two distant quantum dots
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Malinowski, Filip K., Martins, Frederico, Smith, Thomas B., Bartlett, Stephen D., Doherty, Andrew C., Nissen, Peter D., Fallahi, Saeed, Gardner, Geoffrey C., Manfra, Michael J., Marcus, Charles M., and Kuemmeth, Ferdinand
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Condensed Matter - Mesoscale and Nanoscale Physics ,Quantum Physics - Abstract
The Heisenberg exchange interaction between neighboring quantum dots allows precise voltage control over spin dynamics, due to the ability to precisely control the overlap of orbital wavefunctions by gate electrodes. This allows the study of fundamental electronic phenomena and finds applications in quantum information processing. Although spin-based quantum circuits based on short-range exchange interactions are possible, the development of scalable, longer-range coupling schemes constitutes a critical challenge within the spin-qubit community. Approaches based on capacitative coupling and cavity-mediated interactions effectively couple spin qubits to the charge degree of freedom, making them susceptible to electrically-induced decoherence. The alternative is to extend the range of the Heisenberg exchange interaction by means of a quantum mediator. Here, we show that a multielectron quantum dot with 50-100 electrons serves as an excellent mediator, preserving speed and coherence of the resulting spin-spin coupling while providing several functionalities that are of practical importance. These include speed (mediated two-qubit rates up to several gigahertz), distance (of order of a micrometer), voltage control, possibility of sweet spot operation (reducing susceptibility to charge noise), and reversal of the interaction sign (useful for dynamical decoupling from noise)., Comment: 6 pages including 4 figures, plus 8 supplementary pages including 5 supplementary figures
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- 2018
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17. Performance of quantum error correction with coherent errors
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Huang, Eric, Doherty, Andrew C., and Flammia, Steven
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Quantum Physics - Abstract
We compare the performance of quantum error correcting codes when memory errors are unitary with the more familiar case of dephasing noise. For a wide range of codes we analytically compute the effective logical channel that results when the error correction steps are performed noiselessly. Our examples include the entire family of repetition codes, the 5-qubit, Steane, Shor, and surface codes. When errors are measured in terms of the diamond norm, we find that the error correction is typically much more effective for unitary errors than for dephasing. We observe this behavior for a wide range of codes after a single level of encoding, and in the thresholds of concatenated codes using hard decoders. We show that this holds with great generality by proving a bound on the performance of any stabilizer code when the noise at the physical level is unitary. By comparing the diamond norm error $D'_\diamond$ of the logical qubit with the same quantity at the physical level $D_\diamond$, we show that $D'_\diamond \le c D^d_\diamond $ where $d$ is the distance of the code and $c$ is constant that depends on the code but not on the error. This bound compares very favorably to the performance of error correction for dephasing noise and other Pauli channels, where an error correcting code of odd distance $d$ will exhibit a scaling $D'_\diamond \sim D_\diamond^{(d+1)/2}$., Comment: 26 pages, 3 figures. See also related work by Beale, Wallman, Gutierrez, Brown, and Laflamme
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- 2018
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18. Optimizing practical entanglement distillation
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Rozpędek, Filip, Schiet, Thomas, Thinh, Le Phuc, Elkouss, David, Doherty, Andrew C., and Wehner, Stephanie
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Quantum Physics - Abstract
The goal of entanglement distillation is to turn a large number of weakly entangled states into a smaller number of highly entangled ones. Practical entanglement distillation schemes offer a tradeoff between the fidelity to the target state, and the probability of successful distillation. Exploiting such tradeoffs is of interest in the design of quantum repeater protocols. Here, we present a number of methods to assess and optimize entanglement distillation schemes. We start by giving a numerical method to compute upper bounds on the maximum achievable fidelity for a desired probability of success. We show that this method performs well for many known examples by comparing it to well-known distillation protocols. This allows us to show optimality for many well-known distillation protocols for specific states of interest. As an example, we analytically prove optimality of the distillation protocol utilized within the Extreme Photon Loss (EPL) entanglement generation scheme, even in the asymptotic limit. We proceed to present a numerical method that can improve an existing distillation scheme for a given input state, and we present an example for which this method finds an optimal distillation protocol. An implementation of our numerical methods is available as a Julia package., Comment: 15+21 pages, 13 figures. v2: "realistic operations (RO)" renamed to "measure and exchange (MX) operations", published version
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- 2018
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19. Coupling Two Spin Qubits with a High-Impedance Resonator
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Harvey, S. P., Bøttcher, C. G. L., Orona, L. A., Bartlett, S. D., Doherty, A. C., and Yacoby, A.
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Quantum Physics ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
Fast, high-fidelity single and two-qubit gates are essential to building a viable quantum information processor, but achieving both in the same system has proved challenging for spin qubits. We propose and analyze an approach to perform a long-distance two-qubit controlled phase (CPHASE) gate between two singlet-triplet qubits using an electromagnetic resonator to mediate their interaction. The qubits couple longitudinally to the resonator, and by driving the qubits near the resonator's frequency they can be made to acquire a state-dependent geometric phase that leads to a CPHASE gate independent of the initial state of the resonator. Using high impedance resonators enables gate times of order 10 ns while maintaining long coherence times. Simulations show average gate fidelities of over 96% using currently achievable experimental parameters and over 99% using state-of-the-art resonator technology. After optimizing the gate fidelity in terms of parameters tuneable in-situ, we find it takes a simple power-law form in terms of the resonator's impedance and quality and the qubits' noise bath., Comment: 11 pages, 2 figures
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- 2018
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20. Predictors of critical care, mechanical ventilation, and mortality among hospitalized patients with COVID-19 in an electronic health record database
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Chomistek, Andrea K., Liang, Caihua, Doherty, Michael C., Clifford, C. Robin, Ogilvie, Rachel P., Gately, Robert V., Song, Jennifer N., Enger, Cheryl, Lin, Nancy D., Wang, Florence T., and Seeger, John D.
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- 2022
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21. Spin of a multielectron quantum dot and its interaction with a neighboring electron
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Malinowski, Filip K., Martins, Frederico, Smith, Thomas B., Bartlett, Stephen D., Doherty, Andrew C., Nissen, Peter D., Fallahi, Saeed, Gardner, Geoffrey C., Manfra, Michael J., Marcus, Charles M., and Kuemmeth, Ferdinand
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We investigate the spin of a multielectron GaAs quantum dot in a sequence of nine charge occupancies, by exchange coupling the multielectron dot to a neighboring two-electron double quantum dot. For all nine occupancies, we make use of a leakage spectroscopy technique to reconstruct the spectrum of spin states in the vicinity of the interdot charge transition between a single- and a multielectron quantum dot. In the same regime we also perform time-resolved measurements of coherent exchange oscillations between the single- and multielectron quantum dot. With these measurements, we identify distinct characteristics of the multielectron spin state, depending on whether the dot's occupancy is even or odd. For three out of four even occupancies we do not observe any exchange interaction with the single quantum dot, indicating a spin-0 ground state. For the one remaining even occupancy, we observe an exchange interaction that we associate with a spin-1 multielectron quantum dot ground state. For all five of the odd occupancies, we observe an exchange interaction associated with a spin-1/2 ground state. For three of these odd occupancies, we clearly demonstrate that the exchange interaction changes sign in the vicinity of the charge transition. For one of these, the exchange interaction is negative (i.e. triplet-preferring) beyond the interdot charge transition, consistent with the observed spin-1 for the next (even) occupancy. Our experimental results are interpreted through the use of a Hubbard model involving two orbitals of the multielectron quantum dot. Allowing for the spin correlation energy (i.e. including a term favoring Hund's rules) and different tunnel coupling to different orbitals, we qualitatively reproduce the measured exchange profiles for all occupancies., Comment: 20 pages, 13 figures, 2 tables
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- 2017
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22. Tensor Networks with a Twist: Anyon-permuting domain walls and defects in PEPS
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Bridgeman, Jacob C., Bartlett, Stephen D., and Doherty, Andrew C.
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Quantum Physics ,Condensed Matter - Strongly Correlated Electrons - Abstract
We study the realization of anyon-permuting symmetries of topological phases on the lattice using tensor networks. Working on the virtual level of a projected entangled pair state, we find matrix product operators (MPOs) that realize all unitary topological symmetries for the toric and color codes. These operators act as domain walls that enact the symmetry transformation on anyons as they cross. By considering open boundary conditions for these domain wall MPOs, we show how to introduce symmetry twists and defect lines into the state., Comment: 11 pages, 6 figures, 2 appendices, v2 published version
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- 2017
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23. Long-range entanglement for spin qubits via quantum Hall edge modes
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Elman, Samuel J., Bartlett, Stephen D., and Doherty, Andrew C.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Quantum Physics - Abstract
We propose and analyse a scheme for performing a long-range entangling gate for qubits encoded in electron spins trapped in semiconductor quantum dots. Our coupling makes use of an electrostatic interaction between the state-dependent charge configurations of a singlet-triplet qubit and the edge modes of a quantum Hall droplet. We show that distant singlet-triplet qubits can be selectively coupled, with gate times that can be much shorter than qubit dephasing times and faster than decoherence due to coupling to the edge modes. Based on parameters from recent experiments, we argue that fidelities above 99% could in principle be achieved for a two-qubit entangling gate taking as little as 20 ns., Comment: 14 pages, 7 figures, comments welcome; v2 published version
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- 2017
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24. Correction to: Development and Validation of ICD‑10‑CM‑based Algorithms for Date of Last Menstrual Period, Pregnancy Outcomes, and Infant Outcomes
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Chomistek, Andrea K., Phiri, Kelesitse, Doherty, Michael C., Calderbank, Jenna F., Chiuve, Stephanie E., McIlroy, Brenda Hinman, Snabes, Michael C., Enger, Cheryl, and Seeger, John D.
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- 2023
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25. On-Chip Microwave Quantum Hall Circulator
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Mahoney, A. C., Colless, J. I., Pauka, S. J., Hornibrook, J. M., Watson, J. D., Gardner, G. C., Manfra, M. J., Doherty, A. C., and Reilly, D. J.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Quantum Physics - Abstract
Circulators are non-reciprocal circuit elements integral to technologies including radar systems, microwave communication transceivers, and the readout of quantum information devices. Their non-reciprocity arises from the interference of microwaves over the centimetre-scale of the signal wavelength in the presence of bulky magnetic media that break time-reversal symmetry. Here we realize a completely passive on-chip microwave circulator with size one-thousandth the wavelength by exploiting the chiral, slow-light response of a 2-dimensional electron gas (2DEG) in the quantum Hall regime. For an integrated GaAs device with 330 um diameter and 1 GHz centre frequency, a non-reciprocity of 25 dB is observed over a 50 MHz bandwidth. Furthermore, the direction of circulation can be selected dynamically by varying the magnetic field, an aspect that may enable reconfigurable passive routing of microwave signals on-chip.
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- 2016
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26. Comparing Experiments to the Fault-Tolerance Threshold
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Kueng, Richard, Long, David M., Doherty, Andrew C., and Flammia, Steven T.
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Quantum Physics - Abstract
Achieving error rates that meet or exceed the fault-tolerance threshold is a central goal for quantum computing experiments, and measuring these error rates using randomized benchmarking is now routine. However, direct comparison between measured error rates and thresholds is complicated by the fact that benchmarking estimates average error rates while thresholds reflect worst-case behavior when a gate is used as part of a large computation. These two measures of error can differ by orders of magnitude in the regime of interest. Here we facilitate comparison between the experimentally accessible average error rates and the worst-case quantities that arise in current threshold theorems by deriving relations between the two for a variety of physical noise sources. Our results indicate that it is coherent errors that lead to an enormous mismatch between average and worst case, and we quantify how well these errors must be controlled to ensure fair comparison between average error probabilities and fault-tolerance thresholds., Comment: 5 pages, 2 figures, 13 page appendix
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- 2015
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27. Characterisation of an exchange-based two-qubit gate for resonant exchange qubits
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Wardrop, Matthew P. and Doherty, Andrew C.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Quantum Physics - Abstract
Resonant exchange qubits are a promising addition to the family of experimentally implemented encodings of single qubits using semiconductor quantum dots. We have shown previously that it ought to be straightforward to perform a CPHASE gate between two resonant exchange qubits with a single exchange pulse. This approach uses energy gaps to suppress leakage rather than conventional pulse sequences. In this paper we present analysis and simulations of our proposed two-qubit gate subject to charge and Overhauser field noise at levels observed in current experiments. Our main result is that we expect implementations of our two-qubit gate to achieve high fidelities, with errors at the percent level and gate times comparable to single-qubit operations. As such, exchange-coupled resonant exchange qubits remain an attractive approach for quantum computing., Comment: 11 pages, 8 figures + 4 pages of supp. mat., 1 figure, comments welcome
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- 2015
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28. Symmetry-respecting real-space renormalization for the quantum Ashkin-Teller model
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O'Brien, Aroon, Bartlett, Stephen D., Doherty, Andrew C., and Flammia, Steven T.
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Condensed Matter - Strongly Correlated Electrons ,Quantum Physics - Abstract
We use a simple real-space renormalization group approach to investigate the critical behavior of the quantum Ashkin-Teller model, a one-dimensional quantum spin chain possessing a line of criticality along which critical exponents vary continuously. This approach, which is based on exploiting the on-site symmetry of the model, has been shown to be surprisingly accurate for predicting some aspects of the critical behavior of the Ising model. Our investigation explores this approach in more generality, in a model where the critical behavior has a richer structure but which reduces to the simpler Ising case at a special point. We demonstrate that the correlation length critical exponent as predicted from this real-space renormalization group approach is in broad agreement with the corresponding results from conformal field theory along the line of criticality. Near the Ising special point, the error in the estimated critical exponent from this simple method is comparable to that of numerically-intensive simulations based on much more sophisticated methods, although the accuracy decreases away from the decoupled Ising model point., Comment: 8 pages, 5 figures, comments welcome; v2 fixed an error in the analytic expression against which we compare our numerical results, added new references; v3 published version
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- 2015
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29. Cavity mediated coherent coupling of magnetic moments
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Lambert, N. J., Haigh, J. A., Langenfeld, S., Doherty, A. C., and Ferguson, A. J.
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We demonstrate the long range strong coupling of magnetostatic modes in spatially separated ferromagnets mediated by a microwave frequency cavity. Two spheres of yttrium iron garnet are embedded in the cavity and their magnetostatic modes probed using a dispersive measurement technique. We find they are strongly coupled to each other even when detuned from the cavity modes. We investigate the dependence of the magnet-magnet coupling on the cavity detuning $\Delta$, and find a $1/\Delta$ dependence also characteristic of cavity-coupled superconducting qubits. Dark states of the coupled magnetostatic modes of the system are observed, and ascribed to mismatches between the symmetries of the modes and the drive field., Comment: 13 pages, 4 figures
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- 2015
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30. Dispersive read-out of ferromagnetic resonance for strongly coupled magnons and microwave photons
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Haigh, J. A., Lambert, N. J., Doherty, A. C., and Ferguson, A. J.
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We demonstrate the dispersive measurement of ferromagnetic resonance in a yttrium iron garnet sphere embedded within a microwave cavity. The reduction in the longitudinal magnetization at resonance is measured as a frequency shift in the cavity mode coupled to the sphere. This measurement is a result of the intrinsic non-linearity in magnetization dynamics, indicating a promising route towards experiments in magnon cavity quantum electro-dynamics., Comment: 5 pages, 5 figures
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- 2015
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31. MERA for Spin Chains with Continuously Varying Criticality
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Bridgeman, Jacob C., O'Brien, Aroon, Bartlett, Stephen D., and Doherty, Andrew C.
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Condensed Matter - Strongly Correlated Electrons ,Quantum Physics - Abstract
We use the multiscale entanglement renormalisation ansatz (MERA) to numerically investigate three critical quantum spin chains with Z_2 x Z_2 on-site symmetry: a staggered XXZ model, a transverse field cluster model, and the quantum Ashkin-Teller model. All three models possess a continuous one-parameter family of critical points. Along this critical line, the thermodynamic limit of these models is expected to be described by classes of c=1 conformal field theories (CFTs) of two possible types: the S^1 free boson and its Z_2-orbifold. Our numerics using MERA with explicitly enforced Z_2 x Z_2 symmetry allow us to extract conformal data for each model, with strong evidence supporting the identification of the staggered XXZ model and critical transverse field cluster model with the S^1 boson CFT, and the Ashkin-Teller model with the Z_2-orbifold boson CFT. Our first two models describe the phase transitions between symmetry protected topologically ordered phases and trivial phases, which lie outside the usual Landau-Ginsburg-Wilson paradigm of symmetry breaking. Our results show that a range of critical theories can arise at the boundary of a single symmetry protected phase., Comment: 13 pages, 11 figures, comments welcome; v2 published version
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- 2015
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32. Effectiveness of a fortified drink in improving B vitamin biomarkers in older adults: a controlled intervention trial
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Heffernan, Maria, Doherty, Leanne C., Hack Mendes, Roberta, Clarke, Michelle, Hodge, Stephanie, Clements, Michelle, McAnena, Liadhan, Rivelsrud, Mari, Ward, Mary, Strain, J. J., McNulty, Helene, and Brennan, Lorraine
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- 2021
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33. Immune cellular networks underlying recovery from influenza virus infection in acute hospitalized patients
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Nguyen, Thi H. O., Koutsakos, Marios, van de Sandt, Carolien E., Crawford, Jeremy Chase, Loh, Liyen, Sant, Sneha, Grzelak, Ludivine, Allen, Emma K., Brahm, Tim, Clemens, E. Bridie, Auladell, Maria, Hensen, Luca, Wang, Zhongfang, Nüssing, Simone, Jia, Xiaoxiao, Günther, Patrick, Wheatley, Adam K., Kent, Stephen J., Aban, Malet, Deng, Yi-Mo, Laurie, Karen L., Hurt, Aeron C., Gras, Stephanie, Rossjohn, Jamie, Crowe, Jane, Xu, Jianqing, Jackson, David, Brown, Lorena E., La Gruta, Nicole, Chen, Weisan, Doherty, Peter C., Turner, Stephen J., Kotsimbos, Tom C., Thomas, Paul G., Cheng, Allen C., and Kedzierska, Katherine
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- 2021
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34. Engraving Accuracy in Early Modern England : Visual Communication and the Royal Society
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Doherty, Meghan C. and Doherty, Meghan C.
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- 2022
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35. Monica M. White: Freedom farmers: Agricultural resistance and the Black freedom movement: The University of North Carolina Press, Chapel Hill, North Carolina/The United States, 2018, 189 pp, ISBN [978-1-4696-4369-4]
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Doherty, Fiona C.
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- 2021
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36. What have we learnt so far from COVID-19?
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Doherty, Peter C.
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- 2021
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37. WHO 2024 hepatitis B guidelines: an opportunity to transform care
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Easterbrook, Philippa J, Luhmann, Niklas, Bajis, Sahar, Min, Myat Sandi, Newman, Morkor, Lesi, Olufunmilayo, and Doherty, Meg C
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- 2024
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38. Fast spin exchange across a multielectron mediator
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Malinowski, Filip K., Martins, Frederico, Smith, Thomas B., Bartlett, Stephen D., Doherty, Andrew C., Nissen, Peter D., Fallahi, Saeed, Gardner, Geoffrey C., Manfra, Michael J., Marcus, Charles M., and Kuemmeth, Ferdinand
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- 2019
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39. Influenza
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Krammer, Florian, Smith, Gavin J. D., Fouchier, Ron A. M., Peiris, Malik, Kedzierska, Katherine, Doherty, Peter C., Palese, Peter, Shaw, Megan L., Treanor, John, Webster, Robert G., and García-Sastre, Adolfo
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- 2018
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40. Deconvolving mechanisms of particle flux attenuation using nitrogen isotope analyses of amino acids
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Wojtal, Paul K., Doherty, Shannon C., Shea, Connor H., Popp, Brian N., Benitez‐Nelson, Claudia R., Buesseler, Ken O., Estapa, Margaret L., Roca‐Martí, Montserrat, and Close, Hilary G.
- Abstract
Particulate organic matter settling out of the euphotic zone is a major sink for atmospheric carbon dioxide and serves as a primary food source to mesopelagic food webs. Degradation of this organic matter encompasses a suite of mechanisms that attenuate flux, including heterotrophic metabolic processes of microbes and metazoans. The relative contributions of microbial and metazoan heterotrophy to flux attenuation, however, have been difficult to determine. We present results of compound specific nitrogen isotope analysis of amino acids of sinking particles from sediment traps and size‐fractionated particles from in situ filtration between the surface and 500 m at Ocean Station Papa, collected during NASA EXPORTS (EXport Processes in the Ocean from RemoTe Sensing). With increasing depth, we observe: (1) that, based on the δ15N values of threonine, fecal pellets dominate the sinking particle flux and that attenuation of downward particle flux occurs largely via disaggregation in the upper mesopelagic; (2) an increasing trophic position of particles in the upper water column, reflecting increasing heterotrophic contributions to the nitrogen pool and the loss of particles via remineralization; and (3) increasing δ15N values of source amino acids in submicron and small (1–6 μm) particles, reflecting microbial particle solubilization. We further employ a Bayesian mixing model to estimate the relative proportions of fecal pellets, phytodetritus, and microbially degraded material in particles and compare these results and our interpretations of flux attenuation mechanisms to other, independent methods used during EXPORTS.
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- 2023
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41. Sizing up the key determinants of the CD8+ T cell response
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Tscharke, David C., Croft, Nathan P., Doherty, Peter C., and La Gruta, Nicole L.
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- 2015
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42. Distinguishing zooplankton fecal pellets as a component of the biological pump using compound‐specific isotope analysis of amino acids
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Doherty, Shannon C., Maas, Amy E., Steinberg, Deborah K., Popp, Brian N., and Close, Hilary G.
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Zooplankton contribute a major component of the vertical flux of particulate organic matter to the ocean interior by packaging consumed food and waste into large, dense fecal pellets that sink quickly. Existing methods for quantifying the contribution of fecal pellets to particulate organic matter use either visual identification or lipid biomarkers, but these methods may exclude fecal material that is not morphologically distinct, or may include zooplankton carcasses in addition to fecal pellets. Based on results from seven pairs of wild‐caught zooplankton and their fecal pellets, we assess the ability of compound‐specific isotope analysis of amino acids (CSIA‐AA) to chemically distinguish fecal pellets as an end‐member material within particulate organic matter. Nitrogen CSIA‐AA is an improvement on previous uses of bulk stable isotope ratios, which cannot distinguish between differences in baseline isotope ratios and fractionation due to metabolic processing. We suggest that the relative trophic position of zooplankton and their fecal pellets, as calculated using CSIA‐AA, can provide a metric for estimating the dietary absorption efficiency of zooplankton. Using this metric, the zooplankton examined here had widely ranging dietary absorption efficiencies, where lower dietary absorption may equate to higher proportions of fecal packaging of undigested material. The nitrogen isotope ratios of threonine and alanine statistically distinguished the zooplankton fecal pellets from literature‐derived examples of phytoplankton, zooplankton biomass, and microbially degraded organic matter. We suggest that δ15N values of threonine and alanine could be used in mixing models to quantify the contribution of fecal pellets to particulate organic matter.
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- 2021
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43. The Origin of COVID-19 and Why It Matters.
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Morens, David M., Breman, Joel G., Calisher, Charles H., Doherty, Peter C., Hahn, Beatrice H., Keusch, Gerald T., Kramer, Laura D., LeDuc, James W., Monath, Thomas P., and Taubenberger, Jeffery K.
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- 2020
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44. Unruly Objects – Material Entanglements in the Arts and Sciences
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Dacome, Lucia, Doherty, Meghan C., Porter, Dahlia, and Roby, Courtney
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- 2020
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45. Inadequate Communication Exacerbates the Support Needs of Current and Bereaved Caregivers in Advanced Heart Failure and Impedes Shared Decision-making.
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Fitzsimons, Donna, Doherty, Leanne C., Murphy, Mary, Dixon, Lana, Donnelly, Patrick, McDonald, Kenneth, and McIlfatrick, Sonja
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HEART failure ,PSYCHOLOGY of caregivers ,COMMUNICATION ,CONTINUUM of care ,DECISION making ,INTERVIEWING ,RESEARCH methodology ,NEEDS assessment ,PALLIATIVE treatment ,TERMINAL care ,QUALITATIVE research ,SOCIAL support ,THEMATIC analysis ,BURDEN of care ,CAREGIVER attitudes ,PSYCHOLOGY - Abstract
Background: Clinicians face considerable challenges in identifying patients with advanced heart failure who experience significant symptom burden at the end of life. Often, these patients are cared for in the community by a loved one who has limited access to support from specialist services, including palliative care. Aim: The aims of this study were to explore caregivers' experience when caring for a loved one with advanced heart failure at the end of life and to identify any unmet psychosocial needs. Methods: This article reports findings of a qualitative study, using semistructured, one-to-one interviews with current and bereaved caregivers, who participated in a larger mixed-methods study. Interviews were conducted by a trained researcher, digitally recorded, transcribed verbatim, and imported to NVivo 11 for data management and coding. Data were analyzed using thematic analysis and an inductive approach. Results: The 30 interviews included 20 current caregivers and 10 bereaved caregivers. The central feature of the caregivers' experience was identified as being "a physical and emotional rollercoaster." There were 3 main themes identified: poor communication, living with uncertainty, and lack of service provision. These themes were supported by 6 subthemes: inadequate understanding of palliative care, a 24/7 physical burden, emotional burden, inability to plan, no care continuity, and dying lonely and unsupported. Conclusions: Caregivers in advanced heart failure need clearer communication regarding diagnosis and prognosis of their loved one's condition to help with the uncertainty of their situation. Improved identification of palliative care needs and more coordinated service provision are urgently required to address their physical and emotional challenges from diagnosis through bereavement. [ABSTRACT FROM AUTHOR]
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- 2019
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46. A peer-led walking intervention for adolescent girls (the WISH study): a cluster-randomised controlled trial
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Murphy, Marie H, O'Kane, S Maria, Carlin, Angela, Lahart, Ian M, Doherty, Leanne C, Jago, Russell, McDermott, Gary, Faulkner, Maria, and Gallagher, Alison M
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Adolescent girls in the UK and Ireland fail to meet physical activity (PA) guidelines. PA behaviours track from childhood into adulthood. The effects of walking interventions on adult health are known; however, the potential of walking to promote PA in adolescents is less known. This study evaluated the effectiveness of a novel, school-based walking intervention aimed at increasing PA levels of adolescent girls.
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- 2023
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47. Community-Based Treatment for Chronic Edema: An Effective Service Model.
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Moffatt, Christine J., Doherty, Debra C., Franks, Peter J., and Mortimer, Peter S.
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Background: Chronic edema care is patchy and of variable quality internationally. This study was undertaken to develop and evaluate a system of care that would provide for patients within a geographical area of London (Wandsworth), United Kingdom. Methods and Results: A prospective cohort design with intervention of a new service design following a 6-month baseline period. Patients were identified through health professionals. A stratified random sample was drawn from all patients and an implementation strategy developed. Clinical assessment combined with questionnaires evaluated clinical, patient, and health service outcomes at 6-month periods. In all, 312 patients were identified in community and acute services giving a crude ascertainment rate of 1.16 per 1000 population. The random sample of 107 was mostly female (82%) with mean (standard deviation) age of 72.9 (12.4) in men and 68.6 (15.0) years in women. Mean reductions in limb volume achieved statistical differences at 6-12 months after implementation (difference [d] = 115 mL, p = 0.0001). Incidence of cellulitis dropped from 41.5/100 patient years at baseline to zero at 6-12 months. Quality of life showed greatest improvements between baseline and 6 months postimplementation, the largest differences being in role physical (d = 32.7, p = 0.0001) and role emotion (d = 24.0, p < 0.0001). EuroQol increased following implementation by a mean score of 0.05 ( p = 0.007). There was a reduction in 6 monthly healthcare costs from £50171 per 100 patients at baseline to £17618 between 6 and 12 months. Conclusions: This process of implementation improves health outcomes while reducing healthcare costs in patients with lymphedema. [ABSTRACT FROM AUTHOR]
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- 2018
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48. Psychological Factors in Chronic Edema: A Case-Control Study.
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Moffatt, Christine J., Aubeeluck, Aimee, Franks, Peter J., Doherty, Debra C., Mortimer, Peter, and Quere, Isabelle
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Background: To examine psychological health and perceived social support in patients with chronic edema (CE). Methods and Results: A random sample of 107 patients with CE was group matched for age and gender with 102 community controls. The cases had swelling of the arm (38%) and leg (61%) and midline swelling (14%). Cases were more likely to be single or divorced/separated ( p = 0.041) and have reduced mobility ( p < 0.001). They had significantly poorer overall health related quality of life (HRQoL), in particular physical functioning ( p = 0.003); role physical ( p < 0.001); general health ( p = 0.026); vitality ( p = 0.015); social function ( p = 0.007); and role emotional ( p = 0.041). EQ5-D health index scores were significantly reduced in cases by 13 points ( p = <0.001, 95% confidence interval 5.8, 21.6). Cases had similar sized social networks to the control group (5.8 vs. 6.6 p = 0.49), but had lower total perceived social support scores (67.8 vs. 76.1 p = 0.018). CE patients used significantly fewer coping strategies (COPE scale) than controls with regard to the following: active coping ( p = 0.024); planning ( p < 0.001); and use of instrumental support ( p = 0.006). Significantly higher levels of coping were used in restraint ( p = 0.031), positive reinterpretation and growth ( p < 0.001); acceptance (<0.001); denial ( p < 0.001); mental disengagement ( p < 0.001); behavioral disengagement (<0.001); substance abuse ( p = 0.010); and humor ( p < 0.001). Conclusions: Patients with CE have poorer health and greater impact on many aspects of HRQoL. Perceived social support is reduced. Deficits in social function combined with perceived reduction in support, and reduced mental health and emotional scores indicate the risk of psychological issues. Systems of care should offer an environment to address these issues. [ABSTRACT FROM AUTHOR]
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- 2017
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49. Safety study of live, oral human rotavirus vaccine: A cohort study in United States health insurance plans
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Hoffman, Veena, Abu-Elyazeed, Remon, Enger, Cheryl, Esposito, Daina B., Doherty, Michael C., Quinlan, Scott C., Skerry, Kathleen, Holick, Crystal N., Basile, Peter, Friedland, Leonard R., Praet, Nicolas, Wéry, Stéphanie, Willame, Corinne, Dore, David D., and Rosillon, Dominique
- Abstract
ABSTRACTAs part of a regulatory commitment for post-licensure safety monitoring of live, oral human rotavirus vaccine (RV1), this study compared the incidence rates (IR) of intussusception, acute lower respiratory tract infection (LRTI) hospitalization, Kawasaki disease, convulsion, and mortality in RV1 recipients versus inactivated poliovirus vaccine (IPV) recipients in concurrent (cIPV) and recent historical (hIPV) comparison cohorts. Vaccine recipients were identified in 2 claims databases from August 2008 – June 2013 (RV1 and cIPV) and January 2004 – July 2008 (hIPV). Outcomes were identified in the 0–59 days following the first 2 vaccine doses. Intussusception, Kawasaki disease, and convulsion were confirmed via medical record review. Outcome IRs were estimated. Incidence rate ratios (IRRs) were obtained from Poisson regression models. A post-hoc self-controlled case series (SCCS) analysis compared convulsion IRs in a 0–7 day post-vaccination period to a 15–30 day post-vaccination period. We identified 57,931 RV1, 173,384 cIPV, and 159,344 hIPV recipients. No increased risks for intussusception, LRTI, Kawasaki disease, or mortality were observed. The convulsion IRRs were elevated following RV1 Dose 1 (cIPV: 2.07, 95% confidence interval [CI]: 1.27 – 3.38; hIPV: 2.05, 95% CI: 1.24 – 3.38), a finding which is inconclusive as it was observed in only one of the claims databases. The IRR following RV1 Dose 1 in the SCCS analysis lacked precision (2.40, 95% CI: 0.73 – 7.86). No increased convulsion risk was observed following RV1 Dose 2. Overall, this study supports the favorable safety profile of RV1. Continued monitoring for safety signals through routine surveillance is needed to ensure vaccine safety.
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- 2018
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50. Age-Related Decline in Primary CD8+T Cell Responses Is Associated with the Development of Senescence in Virtual Memory CD8+T Cells
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Quinn, Kylie M., Fox, Annette, Harland, Kim L., Russ, Brendan E., Li, Jasmine, Nguyen, Thi H.O., Loh, Liyen, Olshanksy, Moshe, Naeem, Haroon, Tsyganov, Kirill, Wiede, Florian, Webster, Rosela, Blyth, Chantelle, Sng, Xavier Y.X., Tiganis, Tony, Powell, David, Doherty, Peter C., Turner, Stephen J., Kedzierska, Katherine, and La Gruta, Nicole L.
- Abstract
Age-associated decreases in primary CD8+T cell responses occur, in part, due to direct effects on naive CD8+T cells to reduce intrinsic functionality, but the precise nature of this defect remains undefined. Aging also causes accumulation of antigen-naive but semi-differentiated “virtual memory” (TVM) cells, but their contribution to age-related functional decline is unclear. Here, we show that TVMcells are poorly proliferative in aged mice and humans, despite being highly proliferative in young individuals, while conventional naive T cells (TNcells) retain proliferative capacity in both aged mice and humans. Adoptive transfer experiments in mice illustrated that naive CD8 T cells can acquire a proliferative defect imposed by the aged environment but age-related proliferative dysfunction could not be rescued by a young environment. Molecular analyses demonstrate that aged TVMcells exhibit a profile consistent with senescence, marking an observation of senescence in an antigenically naive T cell population.
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- 2018
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