139 research outputs found
Avoiding Loopholes with Hybrid Bell-Leggett-Garg Inequalities
By combining the postulates of macrorealism with Bell locality, we derive a
qualitatively different hybrid inequality that avoids two loopholes that
commonly appear in Leggett-Garg and Bell inequalities. First, locally invasive
measurements can be used, which avoids the "clumsiness" Leggett-Garg inequality
loophole. Second, a single experimental ensemble with fixed analyzer settings
is sampled, which avoids the "disjoint sampling" Bell inequality loophole. The
derived hybrid inequality has the same form as the Clauser-Horne-Shimony-Holt
Bell inequality; however, its quantum violation intriguingly requires weak
measurements. A realistic explanation of an observed violation requires either
the failure of Bell locality, or a preparation-conspiracy of finely tuned and
nonlocally correlated noise. Modern superconducting and optical systems are
poised to implement this test.Comment: 5 pages, 3 figures, published versio
Violating the Modified Helstrom Bound with Nonprojective Measurements
We consider the discrimination of two pure quantum states with three allowed
outcomes: a correct guess, an incorrect guess, and a non-guess. To find an
optimum measurement procedure, we define a tunable cost that penalizes the
incorrect guess and non-guess outcomes. Minimizing this cost over all
projective measurements produces a rigorous cost bound that includes the usual
Helstrom discrimination bound as a special case. We then show that
nonprojective measurements can outperform this modified Helstrom bound for
certain choices of cost function. The Ivanovic-Dieks-Peres unambiguous state
discrimination protocol is recovered as a special case of this improvement.
Notably, while the cost advantage of the latter protocol is destroyed with the
introduction of any amount of experimental noise, other choices of cost
function have optima for which nonprojective measurements robustly show an
appreciable, and thus experimentally measurable, cost advantage. Such an
experiment would be an unambiguous demonstration of a benefit from
nonprojective measurements.Comment: 5 pages, 2 figure
Implementing generalized measurements with superconducting qubits
We describe a method to perform any generalized purity-preserving measurement
of a qubit with techniques tailored to superconducting systems. First, we
consider two methods for realizing a two-outcome partial projection: using a
thresholded continuous measurement in the circuit QED setup, or using an
indirect ancilla qubit measurement. Second, we decompose an arbitrary
purity-preserving two-outcome measurement into single qubit unitary rotations
and a partial projection. Third, we systematically reduce any multiple-outcome
measurement to a sequence of such two-outcome measurements and unitary
operations. Finally, we consider how to define suitable fidelity measures for
multiple-outcome generalized measurements.Comment: 13 pages, 3 figure
Measuring a transmon qubit in circuit QED: dressed squeezed states
Using circuit QED, we consider the measurement of a superconducting transmon
qubit via a coupled microwave resonator. For ideally dispersive coupling,
ringing up the resonator produces coherent states with frequencies matched to
transmon energy states. Realistic coupling is not ideally dispersive, however,
so transmon-resonator energy levels hybridize into joint eigenstate ladders of
the Jaynes-Cummings type. Previous work has shown that ringing up the resonator
approximately respects this ladder structure to produce a coherent state in the
eigenbasis (a dressed coherent state). We numerically investigate the validity
of this coherent state approximation to find two primary deviations. First,
resonator ring-up leaks small stray populations into eigenstate ladders
corresponding to different transmon states. Second, within an eigenstate ladder
the transmon nonlinearity shears the coherent state as it evolves. We then show
that the next natural approximation for this sheared state in the eigenbasis is
a dressed squeezed state, and derive simple evolution equations for such states
using a hybrid phase-Fock-space description.Comment: 18 pages, 8 figures; v2 published versio
Existence of smooth shock profiles for hyperbolic systems with relaxation
The aim of this thesis is the proof of the existence of relaxation shock profiles. The existence results apply if the reduced system is strictly hyperbolic and if the underlying hyperbolic system with relaxation fulfills easy-to-check sructural conditions. In general, the ODE system for the relaxation shock profile has a singular right-hand-side. The structural conditions allow the construction of a locally invariant manifold M, where the vector field to this ODE system has a smooth extenstion from a dense subset of M throughout M and the classical center manifold theorem applies. We apply our results to exponentially based moment closure systems
Spacetime Geometry of Acoustics and Electromagnetism
Both acoustics and electromagnetism represent measurable fields in terms of dynamical potential fields. Electromagnetic force-fields form a spacetime bivector that is represented by a dynamical energy–momentum 4-vector potential field. Acoustic pressure and velocity fields form an energy–momentum density 4-vector field that is represented by a dynamical action scalar potential field. Surprisingly, standard field theory analyses of spin angular momentum based on these traditional potential representations contradict recent experiments, which motivates a careful reassessment of both theories. We analyze extensions of both theories that use the full geometric structure of spacetime to respect essential symmetries enforced by vacuum wave propagation. The resulting extensions are geometrically complete and phase-invariant (i.e., dual-symmetric) formulations that span all five grades of spacetime, with dynamical potentials and measurable fields spanning complementary grades that are related by a spacetime vector derivative (i.e., the quantum Dirac operator). These complete representations correct the equations of motion, energy–momentum tensors, forces experienced by probes, Lagrangian densities, and allowed gauge freedoms, while making manifest the deep structural connections to relativistic quantum field theories. Finally, we discuss the implications of these corrections to experimental tests
Less Neutrophil Extracellular Trap Formation in Term Newborns than in Adults
Background: Newborns are prone to infections, which are independent predictors of neonatal mortality and morbidity. Neutrophil extracellular traps (NETs) are structures composed of chromatin and antimicrobial molecules that capture and kill pathogens. NETs may play an important role in the innate immune system and, thus, might be associated with impaired neonatal immune function. Objectives: This study aimed to compare NET formation between term neonates and healthy adults. We additionally investigated the effects of gestational age, birth weight, mode of delivery, gender, and perinatal infections. Methods: We collected cord blood from 57 term infants (mean gestational age, 39.1 weeks) and 9 late preterm infants (35 weeks), and peripheral blood from 18 healthy adult donors. Neutrophils were isolated, and then NET formation was induced using three different stimulants: N-formylmethionine-leucyl-phenylalanine, phorbol 12-myristate 13-acetate (PMA), or lipopolysaccharide. NETs were immunohistochemically stained and analyzed with regard to NET percentage and NET area. Results: With all three stimuli, healthy term infants showed a lower NET percentage than the adult control group (p < 0.0001 each). The groups also differed in NET area, but the significance level was lower. Following PMA stimulation, we observed greater reductions in NET percentage and NET area in preterm than term infants. Conclusions: The lower NET formation observed in term infants compared to adults likely contributes to the reduced neonatal immune response. NET formation appeared to be even further decreased in late preterm neonates. There remains a need for further investigations of NET formation in more immature preterm infants
Cerebrospinal fluid promotes survival and astroglial differentiation of adult human neural progenitor cells but inhibits proliferation and neuronal differentiation
<p>Abstract</p> <p>Background</p> <p>Neural stem cells (NSCs) are a promising source for cell replacement therapies for neurological diseases. Growing evidence suggests an important role of cerebrospinal fluid (CSF) not only on neuroectodermal cells during brain development but also on the survival, proliferation and fate specification of NSCs in the adult brain. Existing <it>in vitro </it>studies focused on embryonic cell lines and embryonic CSF. We therefore studied the effects of adult human leptomeningeal CSF on the behaviour of adult human NSCs (ahNSCs).</p> <p>Results</p> <p>Adult CSF increased the survival rate of adult human NSCs compared to standard serum free culture media during both stem cell maintenance and differentiation. The presence of CSF promoted differentiation of NSCs leading to a faster loss of their self-renewal capacity as it is measured by the proliferation markers Ki67 and BrdU and stronger cell extension outgrowth with longer and more cell extensions per cell. After differentiation in CSF, we found a larger number of GFAP<sup>+ </sup>astroglial cells compared to differentiation in standard culture media and a lower number of β-tubulin III<sup>+ </sup>neuronal cells.</p> <p>Conclusions</p> <p>Our data demonstrate that adult human leptomeningeal CSF creates a beneficial environment for the survival and differentiation of adult human NSCs. Adult CSF is <it>in vitro </it>a strong glial differentiation stimulus and leads to a rapid loss of stem cell potential.</p
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