Super-Earths and mini-Neptunes dominate the currently discovered exoplanetary populations. With no solar system analog, the origin scenario of these planets continues to be debated. While the rocky planetary cores are still embedded in the gaseous nebula, the rate at which these cores can accrete and build their envelopes is determined primarily by the thermal state of the gas bound to the core. There remains a tension between 3D hydrodynamic models and 1D thermodynamic models whether the outer boundary conditions and the advection of the disk gas into the planetary envelope affect significantly the thermal state of the planet.

In this project, we will revisit the role played by the advection of the disk gas, focusing on the injection of disk entropy into the planet. The proposed project advances previous calculations by employing realistic equations of state and opacities which are known to significantly alter the thermal state and the envelope structure.

The student will build on an existing numerical model written in Python that solves structure equations (a system of coupled ODE describing pressure, mass, and temperature profile of planets) with new physical inputs including the injection of disk entropy. The student will be trained on the application of basic thermodynamics and fluid dynamics in astrophysical research, numerical methods, and using Compute Canada clusters. The student will also benefit from regular group meetings where they will be expected to practice their communication skills.

The project can be conducted in person or online.

For more information contact: Eve Lee (evelee at physics dot mcgill dot ca).

Posted on 2022/01/11

Super-puffs are a rare type of exoplanets which are so puffy that their density is approximately that of cotton candies. Many super-puffs are prone to rapid mass loss so it is a mystery as to how they survive over Gyrs. One hypothesis is that they began with a massive amount of gas (about 2:1 initial gas-to-core mass ratio) and we are catching them as they are currently losing gas at a rate of ~2 Earth masses every Gyr. Most super-puffs appear in multi-planetary systems so it is not obvious whether such copious amounts of mass loss will keep the system stable over its lifetime. The goal of this project is to investigate the stability of multi-planetary systems that harbour super-puffs undergoing rapid mass loss. While we will build a tool that is generally applicable, we will benchmark the calculation to Kepler-223.

The student will modify an open-source N-body code REBOUND (C-version) to simultaneously evolve mass loss and mutual gravitational perturbation in a multi-planetary system. The student will learn the basic physics of exoplanetary mass loss, orbital dynamics, numerical methods, and using Compute Canada clusters. The student will also benefit from regular group meetings where they will be expected to hone their communication skills.

For more information contact: Eve Lee (evelee at physics dot mcgill dot ca).

Posted on 2022/01/11

Particle physics aims to understand, among others, the structure and composition of matter. The Standard Model tries to unify all observables under a single theory of particles and their interactions. This is done experimentally for example at the Large Hadron Collider (LHC) of the research center CERN in Geneva by colliding protons at very high energies and looking at the products of the reaction.

The proposed project would call for the observation of neutral kaons and lambdas particles and the understanding of their backgrounds. So-called Minimum Bias data sets will be used to evaluate production rates and space-time distributions of both signals and backgrounds. It will be possible to make a precise independent measurement of the lifetimes of the particles and thus get a good practical introduction to the field of particle physics and its challenges.

The project would call for familiarization with standard analysis packages, software development for event selection and detailed estimations of the backgrounds, as well as creation of new statistical tools to optimize the signals. Part of the work will be based on previous expertise in the research group. Knowledge of C++ and basic understanding of particle physics concepts would be assets. The student should be based at McGill and work within the ATLAS experimental group, under close and almost daily supervision, with opportunities to interact with the rest of the group and present progresses and results.

For more information contact: François Corriveau (corriveau at physics dot mcgill dot ca).

Posted on 2022/01/13

Experimental particles physics relies on always more precise detectors to investigate interactions produced at particle accelerators such as the Large Hadron Collider (LHC) at CERN or the future International Linear Collider in Japan. Particle Flow Algorithms are the new approach to optimize measurements, by combining full information from all detectors. It also requires unprecedented high granularity of the calorimeter detectors, with cells down to the cubic centimeter range. The international CALICE collaboration, in which McGill actively participates, is the largest R&D endeavor of these new concepts and developments.

The research project consists in analyzing the data taken by two CALICE prototypes of high granularity hadronic detectors, the Analog version (AHCAL) and the Digital one (DHCAL), in understanding their different principles and in comparing their responses and performances in terms of linearity or energy and space resolutions for different types of particles. The basic analysis tools are already available, but code specific to the project should be developed. This projects will provide leading edge insights into the new techniques and their actual applications in current and future detectors.

Strong motivation and commitment are expected. The candidate should be familiar with C programming and preferably already computer fluent under Linux. The work should take place at McGill under daily supervision. Basic understanding of particle physics concepts would be an asset.

For more information contact: François Corriveau (corriveau at physics dot mcgill dot ca).

Posted on 2022/01/13

The Deep Dish Development Array (D3A) is a small radio interferometer test bed that is sited at the Dominion Radio Astrophysical Observatory in Penticton. D3A is being used to develop and characterize novel instrumentation that will ultimately be used for the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) and the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX). CHORD and HIRAX aim to map three-dimensional large-scale structure in the universe through measurements of redshifted 21-cm emission of neutral hydrogen. The distribution of matter encodes a faint imprint, known as baryon acoustic oscillations (BAOs), that correspond to remnant ripples left behind by sound waves echoing through the plasma of the early universe. Precise measurements of BAOs will allow us to understand the universe's expansion history and probe the nature of dark energy. Realizing these science goals depends critically upon high-precision radio instrumentation. The aim of this proposed project is to test CHORD/HIRAX hardware subsystems and calibration techniques using the D3A test bed.

The student who takes on this project will have the opportunity to work on a variety of CHORD/HIRAX instrumentation using the D3A. Possible areas of work include designing and/or constructing receiver mounts, characterizing active feeds and RF-over-fiber electronics, building auxiliary calibration apparatus, and analyzing data to assess subsystem performance. In addition to developing a broad spectrum of experimental skills, the student will also gain exposure to working within a multi-institution collaborative setting.

Plan B: Some of the subsystem tests can be conducted in our lab facilities at McGill if travel to Penticton is not possible. We will also have access to data from Penticton, so in the event that local lab access is also restricted, the scope of this project will be reworked to focus mostly on a combination of data analysis and electromagnetic simulations.

For more information contact: Cynthia Chiang (chiang at physics dot mcgill dot ca).

Posted on 2022/01/13

Measurements of the radio sky at ~100 MHz and below have the potential to open a new observational window in the universe's history. At the lowest frequencies (tens of MHz), future observations may allow us to one day probe the cosmic "dark ages," an epoch that is unexplored to date. Measurements at these frequencies are extremely challenging because of radio-frequency interference and ionospheric effects. The state of the art among ground-based measurements dates from the 1960s, when Grote Reber caught brief glimpses of the ~2 MHz sky at low resolution. The Array of Long Baseline Antennas for Taking Radio Observations from the Seventy-ninth parallel (ALBATROS) is a new experiment that aims to map the low-frequency sky using an array of autonomous antenna stations. These antenna stations will observe independently, over long baselines, and will be interferometrically combined offline. One array will be installed at the McGill Arctic Research Station on Axel Heiberg Island, a location that is exceptionally radio-quiet and has reduced ionospheric interference relative to lower-latitude sites.

The student who takes on this project will develop the hardware and/or electronics that are needed for the autonomous antenna stations. Possible areas of work include refining the designs of the antenna and front-end electronics, timing/synchronization tests of the readout electronics, RFI qualification of the fuel cell system that provides power for year-long antenna operation, and field testing the antenna stations at sites within driving distance (e.g. Uapishka Station). In addition to developing a broad spectrum of experimental skills, the student will also gain exposure to working within a multi-institution collaborative setting.

Plan B: If field work is not possible, subsystem development and testing will be conducted in our lab facilities at McGill. If local lab access is also restricted, the scope of this project will be reworked to focus on development of control software, data acquisition, and the analysis pipeline. The readout electronics systems are sufficiently small and portable that testing from home will be a viable option.

For more information contact: Cynthia Chiang (chiang at physics dot mcgill dot ca).

Posted on 2022/01/13

X-ray binaries - binary systems composed of a companion star in orbit with a compact object such as a neutron star or a black hole - are some of the best sources for us to study the properties and behaviour of the jets around neutron stars and black holes. To date, investigation of rapid variability in these systems has been mostly limited to X-ray observations, but new technology is allowing us to extend this analysis to the optical band. VERITAS (veritas.sao.arizona.edu) is a VHE (Very High Energy: E > 100 GeV) gamma-ray telescope that is currently undergoing upgrades that will allow for detailed rapid optical observations of these sources in addition to the traditional gamma-ray observations it has taken in the past. Designing and developing a program to best utilize this instrument in the near future is the key to generating high quality science. In this project, the student would be using VERITAS archival data from flaring sources, as well as open-source data from a variety of instruments, to help develop the elements of such a program - including work on the triggering criteria, estimated flux levels and variability of different classes of sources, and an optimal observation strategy.

For more information contact: Ken Ragan (ragan at physics dot mcgill dot ca).

Posted on 2022/01/19

Cloud chambers (see: https://en.wikipedia.org/wiki/Cloud_chamber) can be used to detect charged particle tracks from radioactive sources or from ambient cosmic rays, and are useful for visualization and outreach. They're also just really cool toys!

This project will consist of designing, building, and commissioning such a small detector, using Peltier cooling devices. The successful applicant will do some preliminary research to establish parts, materials, techniques, and approaches, and will then use design software to formalize those into specifications, drawings, and plans. The construction will be done with a combination of 3-D printing and machine-shop work (if necessary). The goal will be a working, easy-to-use table-top-sized detector, suitable for classroom and outreach demonstrations.

For more information contact:
Thomas Brunner (thomas dot brunner at physics dot mcgill dot ca),
Dominic Ryan (dominic at physics dot mcgill dot ca),
Ken Ragan (ragan at physics dot mcgill dot ca).

Posted on 2021/01/21

We are developing an imaging device for hard X-rays and soft gamma rays in the energy range from 0.2 to 2 MeV. Such a detector is useful in safety and security applications where radioactive sources are involved.

An incoming photon will Compton scatter in the detector's front layer and the resulting scattered photon will be absorbed in the detector's rear layer. Knowing the positions and energy deposits associated with these two events enables us to reconstruct the arrival direction of the incident photon up to an azimuthal ambiguity. This ambiguity is resolved by detecting multiple events.

We plan to use CsI scintillator material in the form of bars read out at each end by photomultiplier tubes. The novel feature will be that the position of the interaction along the bar will be determined by comparing the pulse heights from the phototubes at opposite ends, and the longitudinal resolution will be optimized by adjusting the gap between cubes of scintillator that make up the bar. In this way we plan to achieve a significant reduction in the number of required readout channels and the associated cost. To further reduce the costs, there will be one bar for the scatter layer and one for the absorber layer but they will both be mounted on translation stages moved by stepper motors. By acquiring data with the bars at different locations one can synthesize a large-aperture detector.

The student will characterize the instrument and participate in design studies leading to a field-deployable version which will emphasize efficiency and ease of use. S/he will develop analysis code and calibration protocols as well as the related documentation. Weekly meetings with the supervisor and daily interactions with other members of the supervisor's group will keep the research on track. A written report will be submitted at the end of the summer. Experience with electronics and knowledge of Python and Matlab is an asset but not a requirement.

For more information contact: David Hanna (hanna at physics dot mcgill dot ca).

Posted on 2021/01/27

In this collaborative project between the Reisner and Grutter groups, the USRA student will help develop a new technique for making precisely positioned sub 5 nm nanopores. The successful ndemonstration of nanopore sequencing via engineered protein pores has created considerable industrial interest in nanopore based technologies. The next research frontier in nanopore physics is the development of solid-state nanopore devices, which admit of more scalable fabrication processes and will potentially have higher resolution, decreasing the high sequencing error-rates that are currently the main drawback in nanopore sequencing. We have developed a new approach for fabrication of sub 5 nm pores via local dielectric breakdown induced by a conductive AFM tip across a ~10nm nitride membrane. In our approach, a conductive AFM tip is brought into contact with a nitride membrane sitting on top of an electrolyte reservoir. Application of a voltage pulse leads within seconds to formation of a nanoscale pore that can be detected by a subsequent AFM scan. This method combines the ease of classic dielectric breakdown with the nanoscale pore positioning capability of high energy particle milling techniques such as TEM and FIB.

The student will learn all aspects of the pore-making and characterization process and enable interfacing of pores with chips containing nanochannels. In particular, the student will learn how to fabricate pores via AFM, characterize these devices using IV measurements performed with a patch-clamp amplifier, and then either explore fabrication physics in greater depth or use this approach to fabricate nanofluidic devices containing two closely separated nano pores for controlled translocation. Note that the Grutter and Reisner labs are next door to each other on the 4th floor of the Rutherford building; pores are fabricated in one lab and then walked over and characterized in the other, so use of facilities in both labs is clearly focused towards one project. Professor Reisner will be the primary supervisor with meetings taking place once a week; monthly meetings will take place between all projects participants, including Prof. Grutter. If pandemic conditions prevent on-site research, the student instead will perform Comsol simulations of pore formation process and ionic transport through pores.

For more information contact: Walter Reisner (reisner at physics dot mcgill dot ca).

Posted on 2022/01/31

How do multiple interacting polymers behave in confined environments? This is a fundamental problem in confined polymer physics with important implications in a range of biological systems, from chromosomal segregation and plasmid distribution in dividing bacteria to chromatin organization. The Reisner group is developing nanofluidic assays to explore how multiple polymer molecules behave in confined environments. These in vitro confinement models, where all parameters can be directly controlled, will enable testing of whether simple polymer theories can explain DNA organization in biological systems. In detail, nanofluidics will be used to confine multiple chains, using either hydrodynamic flow to compress multiple molecules against slit barriers in nanochannels, or pneumatic actuated lids to trap molecules in nanocavity structures. Differential staining of the chains will be used to independently assess the conformation of each chain, determine the degree of partitioning/mixing and assess coupled diffusion of the chain center-of-mass positions. Measurements will be performed as a function of cavity dimension, salt concentration, degree of molecular crowding, polymer topology, chain number and chain size.

The student will learn how to perform confined polymer experiments on Reisner lab fluorescence microscopy platforms. This training includes chain staining protocols, nanofluidic device and microscope operation. The student will then develop automated analysis routines in either Matlab or python to extract key qualities from the videomicroscopy data. The student will be supervised in the lab by a PhD student and meet with Prof. Reisner on a weekly basis.

For more information contact: Walter Reisner (reisner at physics dot mcgill dot ca).

Posted on 2022/01/31

There has been some recent debate in the biophysical literature about the speed/energy trade-off in biomolecular computation. In particular, Mean First Passage Time calculations on simple models of immune decision appear at first incompatible with the observed response time of actual T cells. This is contradicted by recent calculations and simulations performed in our group. The resolution of the paradox likely comes from an incorrect definition of the absorbing state in previous Mean First Passage Time calculations. The goal of this project will be to explore analytically and numerically the correct formalism, and to connect it to more recent theoretical work on coarse-grained entropy calculations. The student will use Gillespie simulations to compute Mean First Passage Time in various settings, and will perform/adapt analytical calculations to check simulations. He/she will have daily meetings with the supervisor, as well as regular interactions with all members of the group.

For more information contact: Paul François (paulf at physics dot mcgill dot ca).

Posted on 2022/02/01

There are many different machine learning algorithms performing optimal pattern classifications, but the way information is encoded in neural networks remains obscure. This has practical consequences neural networks can be fooled by different classes of so-called «adversarial perturbations». Recently, broad families of networks with different types of memories have been identified, leading to some different robustness properties, that we could relate to some processes observed in biology. We have studied the learning dynamics itself, and see very clear patterns of memory formation, reminiscent of the dynamics observed in cellular differentiation. The goal of the project will be to mathematically characterize the process of memory formation, using a combination of numerical simulations and analytical calculations on generalized Hopfield networks. He/she will have daily meetings with the supervisor, as well as regular interactions with all members of the group.

For more information contact: Paul François (paulf at physics dot mcgill dot ca).

Posted on 2022/02/01

Non-linear oscillators can entrained, leading to a rich ensemble of dynamical properties (chaos, Arnold tongues, etc). We are studying entrainment of embryonic oscillators implicated in vertebrae formation. Our analysis reveals very specific entrainment response, corresponding to Class I/II excitable networks, but with an added feedback where the period of the oscillator changes with entrainment. This generates a new class of interesting properties, such a phase slipping or bistability. The goal of the project is to study mathematically what happens to the entrainment properties of such oscillator with adaptable period, in particular we expect the emergence of a new structure of Arnold tongues that we will study numerically and analytically. He/she will have daily meetings with the supervisor, as well as regular interactions with all members of the group.

For more information contact: Paul François (paulf at physics dot mcgill dot ca).

Posted on 2022/02/01

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is the first major new telescope to be built on Canadian soil for decades. The telescope will have the capability of mapping the largest volume of the universe ever observed in a single survey. It may unlock mysteries of Dark Energy as well as strange radio bursts that have been seen on the sky. Importantly, it is a new paradigm of telescope - it has no moving parts and images the sky by digitally processing information from several thousand antennas.

The goal for this summer project will be to participate in data analysis of the CHIME project - this may include cosmology and/or radio transients. In addition, the student will contribute to the characterization of the telescope performance and day to day monitoring and evaluation of the telescope data.

The student will be involved with analyzing sky signals from the CHIME telescope to characterize day-scale variations of sky-sources and separate these from the telescope instrumental variations. This will involve writing and testing analysis code, typically written in Python and executed on Compute Canada supercomputers. The student will work alongside graduate students and postdoctoral researchers within the CHIME team. The research will take place in person at McGill University. In the event that in-person meetings are not permitted, it will be accomplished with remote platforms such that the student can work from home.

For more information contact: Matt Dobbs (matt dot dobbs at mcgill dot ca).

Posted on 2022/02/02

Axions are one of the leading candidates to explain the dark matter observed in our Universe. The most common search strategies for axion dark matter involve the interconversion of axions and photons in an external magnetic field. However, axions can also decay to a pair of photons, each with an energy corresponding to roughly half the axion mass. The spontaneous decay rate is too slow to be readily observed, but stimulating radiation can enhance the decay rate by orders of magnitude, in analogy to the physics of lasers. If radiation generated by astrophysical processes is the source of stimulating radiation, then the whole sky should be faintly glowing (monochromatically, in the form of an emission line) due to the decay products of axions. In this project, we will develop a statistical framework for searching for this axion glow in the advent of radio surveys that map spectra over large fractions of the sky. Taking into account different sources of stimulating radiation, we will forecast the sensitivity to new axion parameter space that can be accessed with existing data.

The student will form a simplified model of the sky in terms of the best candidates for producing stimulating radiation (based on source brightness, spectrum and geometry). The student will then determine what the axion afterglow will look over the entire sky like using methods that exist in the literature. Finally, based on the scanning patterns of various telescopes, the student will develop a likelihood for how data would look given the axion parameters. The student will work in tandem with and be closely mentored by a graduate student who has experience working with this kind of axion signal. In the course of carrying out this research, the student will get a taste for the physics of axions, radio astronomy, and statistical inference. The student will also come to my group meeting and benefit from a collaborative environment with lots of peer mentoring and opportunities to hear about other developments in the fast-moving world of dark matter research. This entire project is theoretical in nature and therefore can be done fully remotely if the situation requires it.

For more information contact: Katelin Schutz (kschutz at physics dot mcgill dot ca).

Posted on 2022/02/02

Dark matter could be distributed into relatively discrete concentrations of mass (like primordial black holes) rather than the continuum/fluid distribution that would be expected from particle dark matter. These two scenarios may be differentiated through subtle gravitational lensing signatures that affect the population-level statistics of various standard candles, including cepheids and RR lyrae stars. In particular, if dark matter is not distributed smoothly along the lines of sight to standard candles in our galaxy, then most line-of-sight configurations will cause these candles to be “demagnified” by dark matter clumps deflecting light away from the observer. Occasionally, these stars will be magnified by a clump of dark matter with the right geometry with respect to the line of sight. Both of these effects together contribute to an induced skewness in the distribution of inferred luminosities. In this project, we will use Monte Carlo simulation to populate primordial black hole dark matter in our Galaxy near the lines of sight to cepheids in the Gaia DR2 catalog (which has the added benefit of parallax providing an independent distance measure). We will then quantify the change to the distribution of inferred luminosities of these cepheids to determine whether such an effect could be observable given current uncertainties and systematics; if so, we will forecast the sensitivity of this method to primordial black hole dark matter over a range of black hole masses.

The student will first learn the basics of gravitational lensing and will then run Monte Carlo simulations to determine the weak lensing effect of many black holes near a given line of sight as well as the statistics of the cumulative lensing signal across many lines of sight. The student will also come to my group meeting and benefit from a collaborative environment with lots of peer mentoring and opportunities to hear about other developments in the fast-moving world of dark matter research. This entire project is theoretical in nature and therefore can be done fully remotely if the situation requires it.

For more information contact: Katelin Schutz (kschutz at physics dot mcgill dot ca).

Posted on 2022/02/02

During Cosmic Dawn and the subsequent Epoch of Reionization, first-generation galaxies carved out “bubbles” of ionization around them. Studying the shapes and sizes of these bubbles will enable researchers to understand the nature of these galaxies. Unfortunately, predictions for these bubbles varies from one simulation code to another. Additionally, the input parameters are different from code to code, so apples-to-apples comparisons are difficult. The goal of this project is to provide a mapping between one code (the widely used 21cmFAST) and another (the “z-reion”) code. Upon completion, convenient fitting functions will enable users to figure out what equivalent parameter settings must be used in one code to produce the most similar outputs in the other.

The primary role of the student working on this project is to provide a setting of fitting functions that map the inputs parameters of one reionization simulation code (21cmFAST) to the different parametrization of another simulation code (z-reion). This requires the student to first master the running of 21cmFAST, and to then fit the resulting outputs using the parametrizations of z-reion. This will then be repeated for a wide range of astrophysical and cosmological parameters. Comparisons will be made between newly generated simulations to test our work.

For more information contact: Adrian Liu (acliu at physics dot mcgill dot ca).

Posted on 2022/02/04

The EXO (Enriched Xenon Observatory) collaboration is searching for lepton-number violating neutrino-less double beta decays (0νββ) in Xe-136. A positive observation would require the neutrino to be its own anti-particle, i.e. the neutrino has to be a Majorana particle, and shed light on various open questions in neutrino physics. The EXO collaboration is pursuing the development of the next-generation experiment called nEXO. This advanced detector requires the development of new technologies as well as detailed knowledge of the underlying physical processes to reach a sensitivity goal to the 0νββ half-life of 10²⁸ years.

The Light-only-Liquid Xenon Experiment (LoLX) is located in the Brunner neutrino lab at McGill, and is run by a small collaboration from across Canada with partners in Italy. We work closely with TRIUMF (Canada’s premier particle physics institute), and the local group at McGill is responsible for detector operation and involved in all aspects of the experiment. LoLX is a small liquid xenon detector outfitted with state-of-the-art photon sensors, known as silicon photomultipliers (SiPMs) which are used to detect the 175 nm scintillation light produced by particle interactions in the xenon. SiPMs will be used in next-generation rare event search detectors such as nEXO, as well as dark matter detectors such as Darkside-20k and future planned experiments. SiPMs are analogue photo-sensors which produce an avalanche signal that is read out with dedicated electronics, such as an oscilloscope. These devices are sensitive to individual photons in the deep UV and have incredible timing performance.

The main task for this project is to help develop cutting-edge SiPM pulse-finding and reconstruction techniques alongside experts at McGill and TRIUMF. These techniques will be used to determine the time and size of the light signal from the detector, and will be scaled to 100’s of sensors being read simultaneously, for millions of data events. The accurate reconstruction of photon arrival time is critical for the performance of these sensitive detectors. You will learn about standard techniques in the field of single pulse detection and time series analysis, statistical methods in fitting data to models, as well as the techniques used by scintillation light detectors for measuring particle physics interactions.

This project is aimed at undergraduate students at all levels, and programming experience is an asset. Work will be carried out in C++ and ROOT (CERN’s C++ framework for particle physics analysis), but no specific C++ experience is required. You will be supervised by a PhD student in the local neutrino group, and meet regularly with the LoLX group (Including Prof. Brunner) to discuss the project.

For more information contact: Thomas Brunner (brunner at physics dot mcgill dot ca).

Posted on 2022/02/04

The EXO (Enriched Xenon Observatory) collaboration is searching for lepton-number violating neutrino-less double beta decays (0νββ) in Xe-136. A positive observation would require the neutrino to be its own anti-particle, i.e. the neutrino has to be a Majorana particle, and shed light on various open questions in neutrino physics. The EXO collaboration is pursuing the development of the next-generation experiment called nEXO. This advanced detector requires the development of new technologies as well as detailed knowledge of the underlying physical processes to reach a sensitivity goal to the 0νββ half-life of 10²⁸ years.

We have been developing the Light-only Liquid Xenon (LoLX) experiment at our lab at McGill which aims to measure the emission of Cherenkov light in liquid xenon (LXe), investigate crosstalk between silicon photomultiplier devices, and deepen our understanding of light emission in LXe. These measurements will help constrain our simulation models for nEXO. LoLX may also improve event identification and suppress backgrounds by separating events where one or two electrons are emitted. This summer, we plan to upgrade the LoLX cooling system by installing a new helium compressor and cold head. Operating this upgraded cryogenics system requires new control systems to be developed and tested.

Your main task will be developing the cooling control systems in C/Python using an Arduino and/or Raspberry Pito keep the cryostat stable around -108 Celsius. You will be embedded within the local neutrino group at McGill and learn about particle physics, the use of liquid xenon as a radiation detector, and how to read cryogenic temperatures using thermocouples and RTDs.

This project is aimed at undergraduate students at all levels. All you need is an interest in nuclear/particle physics and a strong willingness to learn. Programming knowledge in any language (C or Python preferred) would be beneficial but is not necessary, as we have local experts who will be happy to teach you. You will apply your knowledge of thermodynamics in a real life experiment, and take part in the commissioning of the upgraded LoLX cryostat by developing PID loops, a control systems technique that is pervasive across many areas of experimental science.

For more information contact: Thomas Brunner (brunner at physics dot mcgill dot ca).

Posted on 2020/02/04

The nEXO (next Enriched Xenon Observatory) collaboration is searching for lepton-number violating neutrino-less double beta decays (0νββ) in Xe-136. A positive observation would require the neutrino to be its own anti-particle, i.e. the neutrino has to be a Majorana particle, and shed light on various open questions in neutrino physics. nEXO requires the development of advanced technologies as well as detailed knowledge of the underlying physical processes to reach a sensitivity goal of 10^28 years. To push the detector sensitivity even further, new technologies are required. One of those is the so-called Ba-tagging technique. Here, the Xe-decay daughter Ba-136 is located inside the detector volume after the decay, extracted from the volume and identified. This Ba-tagging technique will allow the unambiguous identification of ββ decays by clearly distinguishing them from background events. This technique will be particularly important to verify an observation once a positive 0νββ signal has been observed.

A Ba-tagging technique is being developed at McGill with the focus on the extraction and identification of Ba-ions from xenon gas. For systematic studies and to determine the efficiency of the identification process we require a single-Ba-ion source. The summer projects focuses on the optimization and characterization of a laser-driven single Ba-ion source in vacuum and in xenon gas. A pulsed laser beam is focused on a surface with a known elemental composition where it ablates atoms and ions. Ions are guided away from the surface by electrostatic lenses and injected into the ion identification setup. These well-known ions are used to calibrate the identification setup and determine transport efficiencies throughout the system.

You will be working with members of the McGill nEXO group to measure the ion current in our source at various conditions, and analyze and visualize the recorded data. You will join the local EXO group at McGill and learn about neutrino physics, data management, and detection techniques using liquid Xe.

Plan B: If no access to the lab is possible, the data will be collected by a graduate student and you will be analyzing the recorded data. This work will be complemented by ion-transport simulations.

For more information contact: Thomas Brunner (brunner at physics dot mcgill dot ca).

Posted on 2022/02/07

Fast Radio Bursts are a new and mysterious astrophysical phenomenon in which short (few ms) radio bursts appear randomly in the sky. FRBs are thought to be extragalactic due to their dispersion measures that are far higher than the maximum amount available in our Milky Way. With FRB event rates of ~1000 /sky/day, they raise an interesting puzzle regarding their origin, which lie at cosmological distances. Radio pulsars are rapidly rotating, highly magnetized neutron stars. As compact objects, they embody physical extremes of gravity, density and magnetic field. Thanks to their amazing clock-like properties, radio pulsars can be used as cosmic laboratories for a variety of experiments ranging from tests of relativistic gravity to studies of the interstellar medium.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new radio telescope recently built in Penticton, BC. CHIME's great sensitivity and large field-of-view (250 sq deg) enable the detection of many FRBs per day — in contrast to the fewer than 2 dozen discovered since 2007. CHIME is also an excellent pulsar observatory, able to detect hundreds of pulsars every day and enabling novel experiments using these high cadence observations.

Here are proposed several possible research projects involving data from CHIME. Possibilities include improving FRB characterization, studying repeating FRBs, localizing FRBs, monitoring radio pulsars, and developing software tools to search for pulsars with CHIME.

The student, who should have experience and familiarity with programming in the Linux environment, will be given astrophysical data sets from CHIME to first familiarize themselves with source properties. Then, depending on exact interest, will analyze existing data obtained in order to understand FRBs or the radio pulsar population, or help develop and test new algorithms for our new pulsar searching pipeline.

For more information contact: Victoria Kaspi (vkaspi at physics dot mcgill dot ca).

Posted on 2022/02/09

(2 positions available)

Subatomic physics aims to understand the nature of the basic building blocks of the universe and the laws that explain their behaviour. One approach to do so is to study the results of high energy particle collisions produced in a controlled laboratory environment. The highest energy particle collider in the world is the Large Hadron Collider (LHC) located at the CERN laboratory in Geneva. In order to more precisely study properties of the Higgs boson, study extremely rare physics processes at the subatomic scale that have never been observed before, and search for hints of new physics, the LHC is scheduled to undergo a major upgrade in 2026-28 that will result in an increase of its beam intensity by an order of magnitude. The results of these proton-proton collisions will be recorded by the ATLAS detector, which requires major upgrades to all its subsystem in order to operate at high particle beam intensity. One of these upgrades consists in replacing the entire readout electronics of the Liquid Argon Calorimeter detector, a sub-system responsible for precisely measuring the energy of electrons/photons produced in proton-proton collisions.

The goal of this summer research project is to participate in the ongoing design and development of the future electronics readout. The students will take part in tasks such as the development of the lab infrastructure at McGill and development of analysis/monitoring tools for performing integration tests of different digital electronic components, the running of different integration tests, analysis of digital signals, simulation and validation of digital algorithms implemented in the FPGA, possible contributions to the development of the firmware environment used by the international project, and possible contributions to FPGA firmware programming.

The students will develop a variety of experimental skills, learn about particle detector instrumentation, different concepts of analogue and digital electronics, and develop familiarity with the use of FPGAs.

Research activities will take place in person at McGill University. The students will work alongside other members of the McGill ATLAS research group (research associates, engineer and graduate student), as well as closely collaborate with colleagues at other institutes in Canada and internationally.

The students are required to be resourceful, curious and have a strong desire to learn. Knowledge and experience with computers (unix-based OS, shell scripts, python, C++, git) is considered an asset.

Plan B: In the event that lab work at McGill is not possible due to pandemic-related restrictions, research activities will be conducted using platforms allowing the student to work remotely from home. In this case, the students will work on a subset of the tasks described above that can be performed remotely.

For more information contact: Brigitte Vachon (brigitte dot vachon at mcgill dot ca).

Posted on 2022/02/09

Subatomic physics aims to understand the nature of the basic building blocks of the universe and the laws that explain their behaviour. One approach to do so is to study the results of high energy particle collisions produced in a controlled laboratory environment.

The student will participate in the analysis of proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider (LHC). Specifically, the student will participate in the investigation of the electroweak force of nature through the search for evidence of extremelly rare reactions predicted to exist but never observed before. The student tasks will involve writing and validating analysis code written in C++/Python, and based on ROOT analysis libraries.

Research activities will take place in person at McGill University. In the event that in-person meetings are not permitted due to pandemic-related restrictions, research activities will be carried out through online platforms allowing the student to work remotely from home.

The student will learn about particle physics theory, various data analysis techniques, develop programming skills, and familiarity with the use of computer batch systems.

Students are required to be resourceful, curious and have a strong desire to learn. Knowledge and experience with computers (unix-based OS, shell scripts, python, C++, git) is considered an asset.

For more information contact: Brigitte Vachon (brigitte dot vachon at mcgill dot ca).

Posted on 2022/07/09

Cosmic strings lead to signatures in many observational windows which have specific non-Gaussian features in position space. The project will explore the potential of new statistics such as matched filtering and wavelets to identify string signals in 21cm redshift maps.

The student will be using the output from simulations of the 21cm signal at high redshifts which the MSc thesis of David Maibach produced. To date, these simulation results have been analyzed only with three point function statistics applied to two-dimensional projections of the map. The student will first study if matched filtering techniques applied both to two- and three-dimensional statistics can perform better at identifying the cosmic string signals. Depending on the results, other statistics will be applied.

For more information contact: Robert Brandenberger (rhb at physics dot mcgill dot ca).

Posted on 2020/02/14

The interaction of light with a mirrors moving at constant, relativistic velocities was a thought experiment in Einstein’s famous 1905 paper, solved by Lorentz transformation to the mirror frame. The movement of a real, massive mirror at relativistic speeds is impractical due to the energy cost. However as far as the light is concerned, a mirror is simply a reflective boundary between two regions of space. If one instead generates a moving front of reflective space, one can investigate the same physics. Recently, we have performed an experiment whereby a THz light pulse can interact with a relativistic (both sub- and super-luminal) moving front of photoconductivity within a semiconductor-filled waveguide. We showed one can use this interaction to hit pause on the electromagnetic field oscillations and even perform a time-reversal operation. Now we are curious about accelerating these fronts, where the front follows a curved space-time trajectory. Such accelerating fronts have attracted interest in their potential to generate analogue Hawking radiation. The project will investigate THz light interactions with accelerating fronts numerically using finite-difference time-domain modelling, as well as participate in experiments designed to test these models.

The student will modify existing finite difference time domain code to accelerate a photoconductive front. They will work to define the experimental parameters required to observe predicted phenomena, taking feedback from experiments to fine tune their code. The student will produce a robust and well commented numerical code for these simulations, and will meet on a weekly basis with Cooke and graduate student to communicate their findings. They will prepare summary documents outlining the results of simulations on regular intervals and be expected to participate in the writing of a journal article.

For more information contact: David Cooke (cooke at physics dot mcgill dot ca).

Posted on 2022/02/15

During Cosmic Dawn and the subsequent Epoch of Reionization, first-generation galaxies gradually ionized the universe around them. This ionization causes heating, which ironically makes it harder for subsequent gas clouds to collapse to form new stars. Known as reionization feedback, this effect is theoretically expected but is not easy to directly observe. Previous work has suggested that there may be opportunities to spot signatures of reionization feedback in upcoming near-infrared observations, such as those that will be conducted by the SPHEREx satellite. However, the signatures around individual galaxies will be faint. This project will investigate whether it is possible to boost the signal-to-noise ratio by stacking galaxies on top of each other in one's data analysis.

The primary role of the student working on this project is to take already-performed numerical simulations of reionization and to post-process them to investigate the potential of stacking. The student will learn to read in simulation products, carve out small images of galaxies, and investigate how various stacking schemes give different results in terms of the detection signal-to-noise ratio for various satellite missions.

For more information contact: Adrian Liu (acliu at physics dot mcgill dot ca).

Posted on 2022/02/20

The EXO (Enriched Xenon Observatory) collaboration is searching for lepton-number violating neutrinoless double beta decays (0νββ) in Xe-136. A positive observation would require the neutrino to be its own anti-particle, i.e. the neutrino has to be a Majorana particle, and shed light on various open questions in neutrino physics. The EXO collaboration is pursuing the development of the next-generation experiment called nEXO. This advanced detector requires the development of new technologies as well as detailed knowledge of the underlying physical processes to reach a sensitivity goal to the 0νββ half-life of 10²⁸ years.The detector is a single-phase time projection chamber where ionization and scintillation signals are recorded.Interactions within LXe produce anti-correlated scintillation and ionization signals, which will be used to reconstruct the energy, and position, and multiplicity of each event.

Silicon photomultipliers (SiPMs) have been identified as the devices to detect the vacuum-ultraviolet light for nEXO. Methods for function testing the large number of SIPMs used by the detector are being investigated. At McGill we have developed an IV multiplexer thatallows static measurement of up to 105 devices with low leakage current. In addition, our collaborators have been developing models for extracting SiPM nuisance parameters from IV measurements. These efforts will be combined into a ‘turn-key’ solution to characterize SiPMs.

There are both hardware and software tasks required for this project. Using python, the student will develop a computer program that interfaces with the electrometer. The program will load the electrometer data and make calculations, plots, and perform a regression analysis. Afterwards,the student will test SiPMs using the IV multiplexer and the control program that was developed.

This project is aimed at students who have completed a course in experimental methods for physics laboratories since some statistical analysis is required. The work will be done in collaboration with a graduate student and progress will be reported at weekly group meetings. Following the successful completion of the project, the student will have gained practical experience programming hardware, testing/debugging hardware, and data analysis. In case of disruption due to the pandemic, work can proceed remotely.

For more information contact: Thomas Brunner (brunner at physics dot mcgill dot ca).

Posted on 2022/02/21

The scalability of quantum computers is fundamentally limited by decoherence due to random, noisy, uncontrolled environments. Most environmental noise processes are thought to be well described by purely classical sources of fluctuation, due to some unknown random classical parameter in a system's Hamiltonian. However, when qubits couple to some quantum mechanical degrees of freedom (characterized by non-commuting quantum operators), there can be a purely quantum correcation to the noise, giving rise to dynamics that cannot be explained by any classical process.

The goal of this project will be to theoretically identify distinctly quantum effects in models of decoherence based on magnetic (spin) environments. A secondary goal will be to identify any distinct influence of these quantum effects on the performance of simple quantum algorithms.

This theoretical project can be completed either in-person or remotely, as required.

The student assigned to this project will develop (together with the supervisor) numerical and analytical methods to evaluate quantum noise in general and specifically for magnetic (spin) environments, relevant to spin-based quantum computing. The successful applicant will learn about solid-state implementations of quantum computing, quantum algorithsms, and basic aspects of quantum error correction. If the work yields publishable results, the student will participate in writing/editing the paper (under close supervision) and preparation of figures.

For more information contact: Bill Coish (coish at physics dot mcgill dot ca).

Posted on 2022/02/21

In atomic force microscopy (AFM) one of the key components is the microfabricated force sensor. One of the determining factors for the signal to noise of force measurements is the mechanical Q factor of the force sensor. Mounting losses, also known as clamping losses, are a dominant factor of reduced force sensor Q. In this project, the student will develop and test various ideas of force sensor mounts that minimize mechanical clamping losses. Specifically, we would like to use a spring loaded system so that cantilevers can be easily and rapidly mounted without compromising Q. This involves modal analysis, machining designs and testing using an optical system in a vacuum environment.

The student will first familiarize themselves with the operation of an atomic force microscope. Next, a custom built optical characterization system measure mechanical Q factors will need to be adapted to an existing vacuum system. Different mechanical mounting strategies for force sensors will be machined and tested to find one that minimizes clamping losses and thus systematically achieves a high Q force sensor. The student will be supervised on a daily basis by a graduate student and regularly interact with the PI.

Working in an AFM instrumentation group and collaborating with a graduate student as well as Grutter will expose the student to hands-on instrumentation building and characterization. In particular, the student will learn hands-on mechanical design and optical characterization as well as vacuum techniques. They will be exposed to research on a variety of material systems in a world-class AFM group.

In case of COVID-19 restrictions more emphasis will be laid on simulating the mechanical loss mechanisms as a function of design choices using finite element modeling.

For more information contact: Peter Grütter (peter at physics dot mcgill dot ca).

Posted on 2022/02/22

The aim of this project is to develop a method to apply ultrafast (ps) voltage pulses to a sample in an atomic force microscope (AFM). This will enable future ultrafast opto-electronic measurements with spatial resolution using AFM.

Our group has developed ultrafast methods based on AFM techniques to determine properties on a nanometer length scale and ps-fs time scales. The aim is to investigate and understand the role of defects in electronic transport after photoexcitation in systems ranging from 2D van de Waals heterostructures to organic acceptor-donor systems. We have achieved optical pump-probe time resolution of 100fs. Next, we would like to use optical pump - electrical probe methods. To achieve this, we need ultrafast electrical pulse between AFM tip and sample. Optoelectronic switches have been used extensively by various research groups to generate ultrafast electrical pulses.

The goal of the student is to design, build and characterize a system based on step-recovery diodes (SRS) and non-linear transmission lines (NTL) to achieve a pulse train with pulse widths of 20-50ps at MHz repetition cycles. The student will also possibly design coplanar waveguides if simulations prove a substantial improvement versus traditional signal transmission methods such as coax or twisted pair wires. By performing electrical force measurements an autocorrelation of two such pulses can be measured. This allows the detailed pulse shape to be determined. In case of a lab access shutdown more extensive simulation of different switch design choices will be made.

The student will first familiarize themselves with the operational principle of SRS and NTLs. They will then collaborate with the departmental electronic engineer Eamon Egan to simulate and build the fast pulser. The pulser will then need to be incorporated in a suitable AFM sample holder plate. The switch will be tested by measuring an all-electrical pump-probe correlation with the AFM.

Working in an AFM instrumentation group and collaborating with Eamon Egan will expose the student to hands-on instrumentation building and characterization, in particular ultrafast electronics. They will learn and practically implement electronic design, ultrafast methods and autocorrelation pulse characterization using electrostatic AFM measurements. They will be exposed to research on a variety of material systems in a world-class AFM group.

In case of COVID-19 restrictions more emphasis will be laid on simulating the required circuit.

For more information contact: Peter Grutter (peter at physics dot mcgill dot ca).

Posted on 2022/02/22

When making maps of the cosmic microwave background (CMB), the noise from the atmosphere dwarfs the signals we're after. The optimal way of handling the noise is by solving giant least-squares problems where we solve for billions of parameters from trillions of data points. In tests, we see that subtle effects in the noise modelling/least-squares solver can lead to missing signals in the final science maps. However, we do not understand what is giving rise to the missing signals. Until we do, we will struggle to measure the CMB sky with the ~0.1% accuracy that upcoming experiments are targetting.

This project will try various noise models and model setups to map data from the Atacama Cosmology Telescope (ACT). The models will be used to map ACT data on the Compute Canada Niagara cluster, and the student will examine any signal loss in these maps. Hopefully the source of bias will be identified, and improvements to the mapping algorithms will be developed.

For more information contact: Jonathan Sievers (jonathan dot sievers at mcgill dot ca).

Posted on 2022/02/23

Current and upcoming radio telescopes such as CHIME, CHORD, and HIRAX natively work at relatively modest frequency resolution. Some of our science goals, however, require over an order of magnitude improvement in frequency resolution. We can improve the frequency resolution in the GPU-based correlator, but the initial processing of the data introduces unwanted features in the high-resolution data. This project will investigate various ways of improving the frequency resolution, subject to the networking constraints imposed by the huge volume (~10 terabits/s) of data that needs to be processed.

The student will characterize current rechannelization methods, including effects from quantizing the data. They will then work out what the algorithm should optimize, and find a digital filter that best satisfies the optimization criteria. If successful, the upchannelization algorithm will be used in upcoming radio telescopes.

For more information contact: Jonathan Sievers (jonathan dot sievers at mcgill dot ca).

Posted on 2022/02/23

The student will use the 21cmFAST and ARES programs to study the 21-cm brightness temperature between cosmic dawn and reionization. He/she will also adapt a machine learning algorithm we have previously worked on to pick parameters that reproduce a pre-specified 21cm Global signal generated with and without the effect of cosmic strings. Including the effects of cosmic strings will involve modifications of the 21cmFAST simulation code.

The student will modify an existing neural network and train it to predict the parameters that reproduce a pre-specified 21cm Global Signal without strings. If this part is successfully completed, the student will include cosmic strings in the 21cmFAST code. The student will receive training in machine learning, 21-cm cosmology, and scientific python.

In case of pandemic restrictions, supervisions will take place through Zoom.

For more information contact: Oscar Hernandez (oscarh at physics dot mcgill dot ca).

Posted on 2022/02/23