2,427 research outputs found
Suppression of Quantum Scattering in Strongly Confined Systems
We demonstrate that scattering of particles strongly interacting in three
dimensions (3D) can be suppressed at low energies in a quasi-one-dimensional
(1D) confinement. The underlying mechanism is the interference of the s- and
p-wave scattering contributions with large s- and p-wave 3D scattering lengths
being a necessary prerequisite. This low-dimensional quantum scattering effect
might be useful in "interacting" quasi-1D ultracold atomic gases, guided atom
interferometry, and impurity scattering in strongly confined quantum wire-based
electronic devices.Comment: 3 figs, Phys. Rev. Lett. (early November issue
Semiclassical Application of the Mo/ller Operators in Reactive Scattering
Mo/ller operators in the formulation of reaction probabilities in terms of wave packet correlation functions allow us to define the wave packets in the interaction region rather than in the asymptotic region of the potential surface. We combine Mo/ller operators with the semiclassical propagator of Herman and Kluk. This does not involve further approximations and can be used with any initial value representation (IVR) semiclassical propagator. Time propagation in asymptotic regions of the potential due to Mo/ller operators reduces the oscillations of the propagator integrand and improves convergence of the results with respect to the number of trajectories. The effectiveness of Mo/ller operators for semiclassical reaction probability calculation is demonstrated for the collinear hydrogen exchange reaction. Full convergence is achieved and the number of classical trajectories is reduced by a factor of 10 compared to the calculation without Mo/ller operators
Simplified Calculation of the Stability Matrix for Semiclassical Propagation
We present a simple method of calculation of the stability (monodromy) matrix that enters the widely used semiclassical propagator of Herman and Kluk and almost all other semiclassical propagators. The method is based on the unitarity of classical propagation and does not involve any approximations. The number of auxiliary differential equations per trajectory scales linearly rather than quadratically with the system size. Just the first derivatives of the potential surface are needed. The method is illustrated on the collinear H3 system
Teaching for learning with technology: a faculty development initiative at a research university
This paper reviews recent literature addressing the state of
technology in higher education as a backdrop for a faculty
development program offered annually at Northwestern. First,
we will present the state of technology related to teaching in
three areas: (1) the varied institutional interest in technology,
(2) the variance in faculty engagement with technology, and (3)
factors that influence faculty acceptance of technology. Next,
we will introduce Northwestern’s response to the need for
faculty development related to technology, the 5-day Teaching
and Learning with Technology workshop. Finally, we will
present data gathered over two years that demonstrates how
pedagogically-driven technology training can enhance teaching
and encourage faculty to embrace technology in teaching to
accomplish pedagogically-based learning objectives
Current driven rotating kink mode in a plasma column with a non-line-tied free end
First experimental measurements are presented for the kink instability in a
linear plasma column which is insulated from an axial boundary by finite sheath
resistivity. Instability threshold below the classical Kruskal-Shafranov
threshold, axially asymmetric mode structure and rotation are observed. These
are accurately reproduced by a recent kink theory, which includes axial plasma
flow and one end of the plasma column that is free to move due to a
non-line-tied boundary condition.Comment: 4 pages, 6 figure
Pseudo-time Schroedinger equation with absorbing potential for quantum scattering calculations
The Schroedinger equation with an energy-dependent complex absorbing
potential, associated with a scattering system, can be reduced for a special
choice of the energy-dependence to a harmonic inversion problem of a discrete
pseudo-time correlation function. An efficient formula for Green's function
matrix elements is also derived. Since the exact propagation up to time 2t can
be done with only t real matrix-vector products, this gives an unprecedently
efficient scheme for accurate calculations of quantum spectra for possibly very
large systems.Comment: 9 page
Knowledge overconfidence is associated with anti-consensus views on controversial scientific issues
Public attitudes that are in opposition to scientific consensus can be disastrous and include rejection of vaccines and opposition to climate change mitigation policies. Five studies examine the interrelationships between opposition to expert consensus on controversial scientific issues, how much people actually know about these issues, and how much they think they know. Across seven critical issues that enjoy substantial scientific consensus, as well as attitudes toward COVID-19 vaccines and mitigation measures like mask wearing and social distancing, results indicate that those with the highest levels of opposition have the lowest levels of objective knowledge but the highest levels of subjective knowledge. Implications for scientists, policymakers, and science communicators are discussed
Passive coherent discriminator using phase diversity for the simultaneous measurement of frequency noise and intensity noise of a continuous-wave laser
The frequency noise and intensity noise of a laser set the performance limits in many modern photonics applications and, consequently, must often be characterized. As lasers continue to improve, the measurement of these noises however becomes increasingly challenging. Current approaches for the characterization of very high-performance lasers often call for a second laser with equal or higher performance to the one that is to be measured, an incoherent interferometer having an extremely long delay-arm, or an interferometer that relies on an active device. These instrumental features can be impractical or problematic under certain experimental conditions. As an alternative, this paper presents an entirely passive coherent interferometer that employs an optical 90° hybrid coupler to perform in-phase and quadrature detection. We demonstrate the technique by measuring the frequency noise power spectral density of a highly-stable 192 THz (1560 nm) fiber laser over five frequency decades. Simultaneously, we are able to measure its relative intensity noise power spectral density and characterize the correlation between its amplitude noise and phase noise. We correct some common misconceptions through a detailed theoretical analysis and demonstrate the necessity to account for normal imperfections of the optical 90° hybrid coupler. We finally conclude that this passive coherent discriminator is suitable for reliable and simple noise characterization of highly-stable lasers, with bandwidth and dynamic range benefits but susceptibility to additive noise contamination.V Michaud-Belleau, H Bergeron, P S Light, N B Hébert, J D Deschênes, A N Luiten and J Genes
Boundary Conditions on Internal Three-Body Wave Functions
For a three-body system, a quantum wave function with definite
and quantum numbers may be expressed in terms of an internal wave
function which is a function of three internal coordinates. This
article provides necessary and sufficient constraints on to
ensure that the external wave function is analytic. These
constraints effectively amount to boundary conditions on and its
derivatives at the boundary of the internal space. Such conditions find
similarities in the (planar) two-body problem where the wave function (to
lowest order) has the form at the origin. We expect the boundary
conditions to prove useful for constructing singularity free three-body basis
sets for the case of nonvanishing angular momentum.Comment: 41 pages, submitted to Phys. Rev.
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