3,774 research outputs found
Low-cost error mitigation by symmetry verification
We investigate the performance of error mitigation via measurement of
conserved symmetries on near-term devices. We present two protocols to measure
conserved symmetries during the bulk of an experiment, and develop a zero-cost
post-processing protocol which is equivalent to a variant of the quantum
subspace expansion. We develop methods for inserting global and local symetries
into quantum algorithms, and for adjusting natural symmetries of the problem to
boost their mitigation against different error channels. We demonstrate these
techniques on two- and four-qubit simulations of the hydrogen molecule (using a
classical density-matrix simulator), finding up to an order of magnitude
reduction of the error in obtaining the ground state dissociation curve.Comment: Published versio
Calculating energy derivatives for quantum chemistry on a quantum computer
Modeling chemical reactions and complicated molecular systems has been
proposed as the `killer application' of a future quantum computer. Accurate
calculations of derivatives of molecular eigenenergies are essential towards
this end, allowing for geometry optimization, transition state searches,
predictions of the response to an applied electric or magnetic field, and
molecular dynamics simulations. In this work, we survey methods to calculate
energy derivatives, and present two new methods: one based on quantum phase
estimation, the other on a low-order response approximation. We calculate
asymptotic error bounds and approximate computational scalings for the methods
presented. Implementing these methods, we perform the world's first geometry
optimization on an experimental quantum processor, estimating the equilibrium
bond length of the dihydrogen molecule to within 0.014 Angstrom of the full
configuration interaction value. Within the same experiment, we estimate the
polarizability of the H2 molecule, finding agreement at the equilibrium bond
length to within 0.06 a.u. (2% relative error).Comment: 19 pages, 1 page supplemental, 7 figures. v2 - tidied up and added
example to appendice
Demonstration of Cross-Reactive Antibodies to Smooth Gram-Negative Bacteria in Antiserum to Escherichia coli J5
We investigated the discrepancy between the broad cross-protection against gram-negative infections afforded by antiserum to Escherichia coli J5 and its apparently narrow cross-reactivity in vitro. Rabbits immunized with J5 bacteria produced antibodies to both the J5 lipopolysaccharide (LPS; titer by ELISA, 1:60,000) and LPS from the Re mutant of Salmonella minnesota (i.e., to the ketodeoxyoctonate [KDO] and lipid A determinants; titer, 1:3,200). In highly diluted antiserum, titers of antibody to J5 LPS were reduced by 28%-41% after adsorption with seven strains of smooth gram-negative bacteria and by only 4% after adsorption with the Re mutant. Smooth gram-negative bacteria adsorbed virtually all antibody to Re LPS. Therefore, rabbit antiserum to J5 contains type-specific antibodies to core determinants distal to KDO that can obscure highly cross-reactive antibodies to lipid A-KDO in vitro. Cross-reactive antibodies are demonstrable by adsorption with whole bacteria at limiting concentrations of antibod
Exchange in silicon-based quantum computer architecture
The silicon-based quantum computer proposal has been one of the intensely
pursued ideas during the past three years. Here we calculate the donor electron
exchange in silicon and germanium, and demonstrate an atomic-scale challenge
for quantum computing in Si (and Ge), as the six (four) conduction band minima
in Si (Ge) lead to inter-valley electronic interferences, generating strong
oscillations in the exchange splitting of two-donor two-electron states. Donor
positioning with atomic scale precision within the unit cell thus becomes a
decisive factor in determining the strength of the exchange coupling--a
fundamental ingredient for two-qubit operations in a silicon-based quantum
computer.Comment: 5 pages, 2 figure
Protecting quantum entanglement from leakage and qubit errors via repetitive parity measurements
Protecting quantum information from errors is essential for large-scale
quantum computation. Quantum error correction (QEC) encodes information in
entangled states of many qubits, and performs parity measurements to identify
errors without destroying the encoded information. However, traditional QEC
cannot handle leakage from the qubit computational space. Leakage affects
leading experimental platforms, based on trapped ions and superconducting
circuits, which use effective qubits within many-level physical systems. We
investigate how two-transmon entangled states evolve under repeated parity
measurements, and demonstrate the use of hidden Markov models to detect leakage
using only the record of parity measurement outcomes required for QEC. We show
the stabilization of Bell states over up to 26 parity measurements by
mitigating leakage using postselection, and correcting qubit errors using
Pauli-frame transformations. Our leakage identification method is
computationally efficient and thus compatible with real-time leakage tracking
and correction in larger quantum processors.Comment: 22 pages, 15 figure
Silicon-based spin and charge quantum computation
Silicon-based quantum-computer architectures have attracted attention because
of their promise for scalability and their potential for synergetically
utilizing the available resources associated with the existing Si technology
infrastructure. Electronic and nuclear spins of shallow donors (e.g.
phosphorus) in Si are ideal candidates for qubits in such proposals due to the
relatively long spin coherence times. For these spin qubits, donor electron
charge manipulation by external gates is a key ingredient for control and
read-out of single-qubit operations, while shallow donor exchange gates are
frequently invoked to perform two-qubit operations. More recently, charge
qubits based on tunnel coupling in P substitutional molecular ions in Si
have also been proposed. We discuss the feasibility of the building blocks
involved in shallow donor quantum computation in silicon, taking into account
the peculiarities of silicon electronic structure, in particular the six
degenerate states at the conduction band edge. We show that quantum
interference among these states does not significantly affect operations
involving a single donor, but leads to fast oscillations in electron exchange
coupling and on tunnel-coupling strength when the donor pair relative position
is changed on a lattice-parameter scale. These studies illustrate the
considerable potential as well as the tremendous challenges posed by donor spin
and charge as candidates for qubits in silicon.Comment: Review paper (invited) - to appear in Annals of the Brazilian Academy
of Science
Anti-inflammatory effects of antidepressant and atypical antipsychotic medication for the treatment of major depression and comorbid arthritis: a case report
Extent: 4p.Introduction: This case report describes the effects of psychotropic treatment, quetiapine in particular, on systemic inflammation, pain, general functioning and major depression in the treatment of a woman with arthritis. Case presentation: A 49-year-old Caucasian Australian woman with arthritis, pain and depression was treated with a course of escitalopram, mirtazapine and quetiapine. Pain levels, general functioning and degree of depressive symptoms were evaluated with a visual analogue scale. Systemic inflammation had been assessed by C-reactive protein serum levels since 2003. C-reactive protein levels, physical pain, symptoms of arthritis and depression decreased significantly during the past 12 months of treatment with quetiapine, while treatment with selective serotonin reuptake inhibitors and mirtazapine remained the same. Conclusions: We suggest that the treatment particularly with quetiapine may have anti-inflammatory effects in arthritis and comorbid major depression, which eventually led to a remission of pain and depression and to normal general function.Bernhard T Baune, Harris Eyr
Demonstration of cross-reactive antibodies to smooth gram-negative bacteria in antiserum to Escherichia coli J5
We investigated the discrepancy between the broad cross-protection against gram-negative infections afforded by antiserum to Escherichia coli J5 and its apparently narrow cross-reactivity in vitro. Rabbits immunized with J5 bacteria produced antibodies to both the J5 lipopolysaccharide (LPS; titer by ELISA, 1:60,000) and LPS from the Re mutant of Salmonella minnesota (i.e., to the ketodeoxyoctonate [KDO] and lipid A determinants; titer, 1:3,200). In highly diluted antiserum, titers of antibody to J5 LPS were reduced by 28%-41% after adsorption with seven strains of smooth gram-negative bacteria and by only 4% after adsorption with the Re mutant. Smooth gram-negative bacteria adsorbed virtually all antibody to Re LPS. Therefore, rabbit antiserum to J5 contains type-specific antibodies to core determinants distal to KDO that can obscure highly cross-reactive antibodies to lipid A-KDO in vitro. Cross-reactive antibodies are demonstrable by adsorption with whole bacteria at limiting concentrations of antibody
Cataloging the radio-sky with unsupervised machine learning: a new approach for the SKA era
We develop a new analysis approach towards identifying related radio
components and their corresponding infrared host galaxy based on unsupervised
machine learning methods. By exploiting PINK, a self-organising map algorithm,
we are able to associate radio and infrared sources without the a priori
requirement of training labels. We present an example of this method using
images from the FIRST and WISE surveys centred towards positions
described by the FIRST catalogue. We produce a set of catalogues that
complement FIRST and describe 802,646 objects, including their radio components
and their corresponding AllWISE infrared host galaxy. Using these data products
we (i) demonstrate the ability to identify objects with rare and unique radio
morphologies (e.g. 'X'-shaped galaxies, hybrid FR-I/FR-II morphologies), (ii)
can identify the potentially resolved radio components that are associated with
a single infrared host and (iii) introduce a "curliness" statistic to search
for bent and disturbed radio morphologies, and (iv) extract a set of 17 giant
radio galaxies between 700-1100 kpc. As we require no training labels, our
method can be applied to any radio-continuum survey, provided a sufficiently
representative SOM can be trained
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