arXiv subjects

Mathieu Couillard

Publications and source records attributed to Mathieu Couillard.

3 recordsLinked to original sources

arXiv2026

Controlling the Inhomogeneous Broadening and Impedance Matching of a Spin Ensemble

We control the spectral distribution of a spin ensemble by applying a magnetic field gradient using an anti-Helmholtz coil inside a dilution refrigerator, and demonstrate impedance matching between the ensemble and a transmission line, achieving -50 dB absorption of incident radiation. This represents a first step toward a spin-ensemble-based quantum memory for itinerant microwave photons. We further model the spectral distribution under the applied gradient to predict the spin-resonator response, and use the device to systematically tune the weak-to-strong coupling transition in both continuous-wave and time-domain pulsed measurements.

quant-ph↗

arXiv2022

Large antiferromagnetic fluctuation enhancement of the thermopower at a critical doping in magnetic semimetal Cr1+dTe2

Cr1+dTe2 is a self-intercalated transition metal dichalcogenide that hosts tunable electronic filling and magnetism in its semimetallic band structure. Recent angle-resolved photoemission spectroscopy (ARPES) studies have unveiled a systematic shift in this semimetallic band structure relative to the chemical potential with increased Cr doping. This report presents the temperature and magnetic field dependence of the longitudinal thermopower Sxx for different Cr1+dTe2 compositions. We show that as doping increases, the sign of Sxx changes from positive to negative at the critical doping level of d ~ 0.5. This observed doping-dependent trend in the thermopower is consistent with the evolution of the semimetallic band structure from ARPES. Importantly, an anomalous enhancement of the thermoelectric response is also observed around d~0.5. Combining information from magnetometry and ARPES measurements, existence of the critical nature of the doping level dc (~0.5) is unveiled in magnetic semimetal Cr1+dTe2, where antiferromagnetic fluctuation and near-Fermi-energy pseudogap formation play a potential vital role in enhancing thermoelectric energy conversion.

cond-mat.mtrl-sci↗

arXiv2022

Measurement of absolute radius, refractive index and dispersion of a long cylinder

Long cylinders, such as optical fibers, are some of the most widely used photonic devices. The radius and refractive index of these fibers are therefore fundamentally important parameters in determining their performance. We have developed a method to determine the absolute radius, refractive index, and chromatic dispersion of a long cylinder using only the resonance wavelengths of the whispering gallery modes around its circumference for two different polarizations. Since this method only requires the measurement of resonance wavelengths, it is non-destructive and it can be performed using standard equipment. As a proof-of-concept, we demonstrate the method on a $125\mu m$ optical fiber and an $80\mu m$ borosilicate capillary fiber with thick walls, obtaining values for the diameter and the refractive index with an accuracy of $2 nm$ and $2\times 10^{-5}$, respectively.

physics.optics↗