45,586 research outputs found
Semiclassics around a phase space caustic: an illustration using the Nelson Hamiltonian
The semiclassical formula for the coherent-state propagator is written in
terms of complex classical trajectories of an equivalent classical system.
Depending on the parameters involved, more than one trajectory may contribute
to the calculation. Eventually, however, two contributing trajectories
coalesce, characterizing what is called phase space caustic. In this case, the
usual semiclassical formula for the propagator diverges, so that a uniform
approximation is required to avoid this singularity. In this paper, we present
a non-trivial application illustrating this scenario, and showing the accuracy
of the uniform formula that we have previously derived.Comment: 6 pages, 2 figure
Accelerated adiabatic quantum gates: optimizing speed versus robustness
We develop new protocols for high-fidelity single qubit gates that exploit and extend theoretical ideas for accelerated adiabatic evolution. Our protocols are compatible with qubit architectures with highly isolated logical states, where traditional approaches are problematic; a prime example are superconducting fluxonium qubits. By using an accelerated adiabatic protocol we can enforce the desired adiabatic evolution while having gate times that are comparable to the inverse adiabatic energy gap (a scale that is ultimately set by the amount of power used in the control pulses). By modelling the effects of decoherence, we explore the tradeoff between speed and robustness that is inherent to shortcuts-to-adiabaticity approaches
ATP as a presynaptic modulator
© 2000 Elsevier Science Inc.There is considerable evidence that ATP acts as a fast transmitter or co-transmitter in autonomic and sensory nerves mostly through activation of ionotropic P2X receptors but also through metabotropic P2Y receptors. By analogy, the observations that ATP is released from stimulated central nervous
system (CNS) nerve terminals and that responses to exogenously added ATP can be recorded in central neurons, lead to the proposal that ATP might also be a fast transmitter in the CNS. However, in spite of
the robust expression of P2 receptor mRNA and binding to P2 receptors in the CNS, the demonstration of central purinergic transmission has mostly remained elusive. We now review evidence to suggest that ATP may also act presynaptically rather than solely postsynaptically in the nervous system.Fundação Ciência e Tecnologia and European nio
Weak values and the quantum phase space
We address the issue of how to properly treat, and in a more general setting,
the concept of a weak value of a weak measurement in quantum mechanics. We show
that for this purpose, one must take in account the effects of the measuring
process on the entire phase space of the measuring system. By using coherent
states, we go a step further than Jozsa in a recent paper, and we present an
example where the result of the measurement is symmetrical in the position and
momentum observables and seems to be much better suited for quantum optical
implementation.Comment: 07 pages, accepted for PR
Nova Eruptions with Infrared Interferometric Observations
Infrared interferometric observations have a great deal of potential to
unravel the nature of the nova eruptions. We suggest that techniques, already
in place, to derive the ejection details at optical wavelengths be used with
infrared interferometric observations to derive parameters such as the ejected
mass in a nova eruption. This is achievable based on modelling the initial
phase of the eruption when the infrared light is dominated by the free-free
thermal process.Comment: To appear in the proceedings of "Physics of Evolved Stars 2015 - A
conference dedicated to the memory of Olivier Chesneau
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Theory of mind and attentional bias to facial emotional expressions: A preliminary study
Theory of mind ability has been associated with performance in interpersonal interactions and has been found to influence aspects such as emotion recognition, social competence, and social anxiety. Being able to attribute mental states to others requires attention to subtle communication cues such as facial emotional expressions. Decoding and interpreting emotions expressed by the face, especially those with negative valence, are essential skills to successful social interaction. The current study explored the association between theory of mind skills and attentional bias to facial emotional expressions. According to the study hypothesis, individuals with poor theory of mind skills showed preferential attention to negative faces over both non-negative faces and neutral objects. Tentative explanations for the findings are offered emphasizing the potential adaptive role of vigilance for threat as a way of allocating a limited capacity to interpret others’ mental states to obtain as much information as possible about potential danger in the social environment
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