Canada

This is a report on a project to interview the student body of the Concordia University Physics Department concerning teacher-students interaction. The goal of this research is to establish an easily implemented guideline of teaching methods for a professor to use in the classroom. Students were asked to complete a questionnaire that included a request to describe the teaching style of their favourite physics professors. They were asked to describe what makes them excellent to the student. A variety of known and successful pedagogic techniques were also presented to ascertain their appeal to students. Follow-up interviews were conducted in order to fully develop the given answers.

CAP Virtual Congress 2021

Student preferences for pedagogic techniques

guideline

lectured-based teaching

physics education

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As you know, first gravitational wave event GW150914(binary black hole) has been oberved by LIGO on Sep. 14, 2015. And most importantly, first binary neutron star coalescence event GW170817 has been observed with a signal noise ratio upto 33, which alows us to make constraints on axion field! Here, we first time use axion charged binary neutron star waveform model to give a constaint on axion field.

Constraints on Axions from GW170817

The nonlinear behavior of absolute stimulated Raman scattering (SRS) near the quarter-critical density is investigated using one-dimensional (1D) Vlasov simulations with parameters relevant to ignition-scale direct-drive coronal plasmas. Numerical Vlasov simulations show that a strong and stable Airy pattern is formed by the Raman light as it is generated near its cutoff density. This pattern self-consistently modulates the density profile below the quarter-critical density. The density modulation superimposed in the linear density profile results in a change in the nature of SRS in lower density region from spatial (convective) amplification to temporal (absolute) growth. In addition, strong Langmuir decay instability (LDI) cascades produce daughter Langmuir waves (LWs) that seed SRS below quarter-critical density. These effects act to broaden the spectrum of reflected light. More interestingly, collapse of the primary LWs is observed near their turning point, producing hot electrons. These observations provide a new explanation of hot electron generation and SRS scattered light spectra for ignition-scale experiments.

Nonlinear development of absolute SRS in ignition-scale direct-drive coronal plasmas

It has been shown beyond reasonable doubt that about 95% of the total energy budget of the universe is given by the dark constituents, namely Dark Matter and Dark Energy. What constitutes Dark Matter and Dark Energy remains to be satisfactorily understood however, despite a number of promising candidates. An associated conundrum is that of coincidence, as to why the Dark Matter and Dark Energy densities are of the same order of magnitude at the present epoch. In an attempt to address these, we consider a quantum potential resulting from a quantum corrected Raychaudhuri/Friedmann Equation in presence of a Bose-Einstein condensate (BEC) of light bosons. For a suitable and physically motivated macroscopic ground state wavefunction of the BEC, we show that a unified picture of the cosmic dark sector can indeed emerge, which also resolves the issue of the coincidence. The effective density of the Dark energy component turns out to be a cosmological constant. Furthermore, comparison with observed data give an estimate of the mass of the constituent bosons in the BEC, which is well within the bounds predicted from other considerations.

On the quantum origin of a dark universe

One striking property of the Landau level spectrum of a Weyl semimetal (WSM) is the existence of a chiral Landau level in which the electrons propagate unidirectionnaly along the magnetic field. This linearly dispersive level profoundly influences the optical properties of the WSM especially if it originates from a tilted Weyl cone. In this talk, we compare the behavior of the magneto-optical Kerr effect (MOKE) in a WSM with that of a normal (i.e. non-topological) metal. We obtain the Kerr angle from the optical conductivity tensor σ_{αβ}(ω) using the minimal model of a WSM developed in Ref. [1] which has four tilted Weyl nodes related by mirror and time-reversal symmetry. In the Voigt configuration, a large peak of the Kerr angle occurs at the plasmon frequency. We show that the blueshift in frequency of this peak with increasing magnetic field is a signature of the chiral anomaly in the MOKE.

[1] S. Bertrand, Jean-Michel Parent, R. Côté, and I. Garate, Phys. Rev. B 100, 075107 (2019).

Magneto-optical Kerr effect and signature of the chiral anomaly in a Weyl semimetal in magnetic field

Superfluid neutron matter is a key ingredient in the composition of neutron stars. The physics of the inner crust is largely dependent on that of its $S$-wave neutron superfluid which has been connected to pulsar glitches and modifications on the neutron star cooling. An accurate description of these effects calls for a model-independent treatment of neutron superfluidity. Ab initio techniques developed for finite systems can be guided to extrapolate to the thermodynamic limit and attain this model-independent extraction of various quantities of infinite superfluid neutron matter. To develop a well-informed extrapolation prescription, we calculated the neutron $^1S_0$ pairing gap using the model-independent odd-even staggering in the context of the particle-conserving, projected Bardeen-Cooper-Schrieffer theory under twisted boundary conditions. While the practice of twisted boundary conditions is standard in solid state physics, and has been used repeatedly in the past to reduce finite-size effects, this is the first time it is employed in the context of pairing. We find that a twist-averaging substantially reduces the finite-size effects, bringing systems with $N>50$ within a $2\%$ error margin from the infinite system. This can significantly reduce extrapolation-related errors in the extraction of superfluid neutron matter quantities.

Superfluid neutrons: from particles to matter

This talk aim to discuss the scattering of particles on quantum superposed states. The fact that one of the initial states is in a superposition implies that the plane wave approximation is not valid anymore which is what we usually do. This will lead to the introduction of Wigner function and a formalism to describe this situation.
We will apply this new formalism to the question of gravitational scattering. The idea will be to put in evidence a quantum effect of gravity due to the superposition. We will compute the cross section and discuss the possibility to observe such a small effect.

Gravitational scattering on quantum superposed states

A state-preserving quantum counting algorithm is used to obtain coefficients of a Lanczos recursion from a single ground state wavefunction on the quantum computer. This is used to compute the continued fraction representation of an interacting Green's function for use in condensed matter, particle physics, and other areas. The wavefunction does not need to be re-prepared at each iteration. The quantum algorithm represents an exponential reduction in memory over known classical methods. An extension of the method to determining the ground state is also discussed.

Lanczos recursion on a quantum computer for the Green's function and ground state

We present a study of the evolution of entanglement entropy of matter and geometry in quantum cosmology. We show that entanglement entropy increases rapidly as the Universe expands, and then saturates to a constant non-zero value. The saturation value of the entropy is a linear function of the energy E associated to the quantum state: S=γE. This result suggests a ‘First Law’ of matter-gravity entanglement entropy in quantum gravity.

Matter-Geometry Entanglement in Quantum Cosmology

Over the last few decades, the study of nuclei and neutron-rich matter from first principles has entered a new era. This has partly been driven by the development of novel interactions between two or three nucleons. In an attempt to produce a systematic expansion, several groups have produced Effective Field Theory (EFT) interactions, whether of finite range (chiral EFT) or zero range (pionless EFT). Pionless EFT has been quite successful in studies of cold-atomic Fermi gases. In this talk, I will present recent Quantum Monte Carlo calculations of 8-particle systems and discuss their impact on 8Be and the physics of alpha clustering. I will also discuss recent work on trying to connect ab initio theory with simpler qualitative pictures. Specifically, I will address the first ever systematic non-perturbative calculations of the single-particle excitation spectrum and of the static response (both for strongly interacting neutron matter). In addition to impacting light and neutron-rich nuclei, this work and this talk also touch upon the physics of ultracold gases and of neutron stars.

From alpha clustering to homogeneous matter

Two-pulse COSY (correlation spectroscopy) EPR (Electron Paramagnetic resonance) sequence, utilized for distance measurements in biological systems using nitroxide biradicals, is investigated both analytically and numerically. The analytical expressions derived here for any orientations of the two nitroxide dipoles with respect to the dipolar axis, oriented at an angle \theta with respect to the magnetic field with respect to the dipolar axis joining the two nitroxide dipoles at the angle, \theta, show that, in general, the coherence transfer from p=0 to the single quantum p=1 state is peaked at the orientation \theta being the magic-angle, {54.7}^\circle, and its supplementary angle, {125.3}^\circle, with a narrow width, implying that there is produced orientational selectivity, by the first \pi/2 pulse. This results in the signal being predominantly determined by those biradicals, whose dipolar axes are at, or near, the magic and its supplementary angle. This is entirely a novel finding, not published in the literature. Furthermore, the analytical treatment shows that the Fourier transforms of the two-pulse COSY signal exhibit peaks at \pm d\times \left(3cos^2\theta-1\right); here d=\frac{2}{3}D, with D being the dipolar-coupling constant.). In addition, there occurs also structural sensitivity of the signal, i.e., its dependence on the orientations of the two nitroxide dipoles during to free evolution over the two coherence states p=+1 and -1. The powder (polycrystalline) averages over the unit sphere, accumulated over 20 sets of Monte-Carlo orientations of the two nitroxide dipole moments reveal that the Pake doublets occur at \pm d. It is concluded that the two-pulse COSY experiment is a preferred technique for distance measurements as compared to other multi-pulse (four, five, six) sequences, as well as two-pulse DQ (double quantum) and five-pulse DQM (double quantum modulation) sequences, because its Pake doublet is the most intense of all the other multi-pulse sequences.

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Constraints on Axions from GW170817

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