Seminar

All-optic fine structure splitting eraser

Reliable entangled photon sources are important for testing fundamentals in quantum mechanics, achieving secure quantum key distribution, among other things. Quantum dots are a hot topic for precisely this need of the scientific community. Quantum dots act as artificial atoms by confining electrons and holes in wells. They emit polarization entangled photons in an exciton-biexciton cascade. The expected entangled state from the cascade is               
The confining potential of these wells can be asymmetric which causes fine structure splitting in the intermediate energy level of the cascade.
 
The presented work offers a way to achieve perfectly entangled photon pairs with quantum dots in vertical nanowires, on demand and with a high count rate. Fine structure splitting is seen in all quantum dot systems whether they are quantum dots in nanowires, micropillars, or, self-assembled quantum dots. This proposal is universal because it can be used to compensate for energy dependent entanglement degradation in all entangled photon sources.
The fine structure splitting in the dot leads to a difference in energy of the photons in different polarizations. This renders the quantum dot system less effective for quantum key distribution applications. Therefore, countering fine structure splitting is highly desirable.

This talk will discuss the approach taken in Quantum Photonic Devices lab to counter the fine structure splitting.

Avenues focusing reference frame independent protocols to enhance free space satellite quantum communications channels

Free-space quantum channels for real world quantum information applications are rapidly emerging, with Canada developing the quantum encryption and science satellite (QEYSSat). For polarization-based systems, one challenge is aligning the reference frame of the polarization states. For example, the physical orientation of the satellites is crucial in maintaining the proper geometric reference frame alignment. However, reference frame independent (RFI) protocols overcome this issue because they don’t require all the polarization states to be fixed. Furthermore, using time bin encoding completely removes the need for a geometric reference, but presents its own challenges when used over a free space channel. In this talk, we will discuss the development done at the University of Waterloo towards the use of reference frame independent protocols for free-space quantum channels. Furthermore, we will discuss the benefits of using time bin encoding over free-space channels, and present our implementations of such systems and what they mean for future QEYSSat missions and applications on other platforms.

Young-June Kim: Alpha-RuCl3: a progress report

Abstract: A bond-dependent anisotropic magnetic interaction called the Kitaev interaction can be found in honeycomb lattice materials with strong spin-orbit coupling, which has made a profound impact on quantum magnetism research. In particular, alpha-RuCl3 has been heralded as a realization of the Kitaev quantum spin liquid state, an elusive new state of matter that harbours Majorana fermions. In this talk, I will give a brief overview of the current status of research on alpha-RuCl3 and discuss recent experimental developments and a few surprising findings using ultra-high-quality samples grown in our laboratory. Our samples have minimal stacking faults even at low temperatures, allowing us to determine the low-temperature crystal structure unambiguously. We also found that the magnetic properties are surprisingly sensitive to the inter-layer configuration, giving rise to various magnetic transition temperatures. We also compare low-energy spin-orbit excitations in various Kitaev materials using resonant inelastic x-ray scattering (RIXS). We found that non-local physics is important for describing the spin-orbit excitations in these materials, in contrast to the conventional belief that local Jeff=1/2 physics is sufficient in these compounds.

Math/CS Seminar Featuring Cihan Okay Bilkent University

In modern homotopy theory, spaces are represented by combinatorial models called simplicial sets. Their elegant formulation gives them great expressive power to capture spaces up to homotopy. Simplicial distributions are basic mathematical objects that mix simplicial sets with probabilities. ...

IQC Math CS Seminar - featuring Mario Szegedy, Rutgers University

Motivated by quantum network applications over classical channels, we initiate the study of n-party resource states from which LOCC protocols can create EPR-pairs between any k disjoint pairs of parties. ...

Seminar Presentation by Richard Germond, Queen's University

A number of astrophysical and cosmological observations suggest that roughly 85% of the matter in the Universe is composed of dark matter, presumed to be a particle outside the standard model of particle physics. Direct detection experiments look for signatures of a dark matter particle scattering with a sensitive detector; of the different technologies used for this, cryogenic detectors are well-suited for detecting low-mass dark matter due to their low energy thresholds.

Introduction to Majorana Topological Qubits

Abstract: This presentation will introduce some of the experimental approaches to building topological qubits and the theories supporting current research. Beginning from the early toy models that first proposed the formation of Majorana bound states, I aim to convey an understanding of why topological qubits are so resistant to decoherence. I will introduce the “ingredients” necessary to build a Majorana device and some of the challenges involved. Finally, I will discuss the field's current state and what might be next on the journey to making topological quantum computing a reality. Neither an understanding of topology nor quantum algorithms are necessary to enjoy this talk!

Categories of Kirchoff Relations

Abstract: I will be talking about the connections between electrical circuits and stabilizer qudit quantum circuits with an eye towards applications to qudit quantum error correction. More formally I will be defining a category dubbed Kirchhoff relations and characterize the maps in this category using parity check matrices. I will then go on to give a universal set of generators for this category and interpret these generators in-terms of electrical elements.

This is work in progress.

Chemistry Seminar Series – Steve Winter, Wake Forest University

Host: A. Wei Tsen

Quantum materials represent a broad class of systems whose experimental response relies directly on entanglement between their underlying degrees of freedom. Modeling of such materials presents a variety of challenges related to a disparate variety of complex behaviours that manifest at different energy scales, and a typical sensitivity of responses to model parameters. In this field, first-principles approaches often provide a vital bridge between experiments and theoretical models. In this talk, I will introduce our numerical strategies for systematically building low-energy models with local charge, spin, and orbital degrees of freedom of arbitrary complexity. I will discuss the insights that these methods have yielded for frustrated magnetic insulators collectively known as "Kitaev materials", which have prompted a recent explosion of interest in quantum magnets where spin-orbit coupling induces strongly anisotropic and competing magnetic interactions. I will specifically address our recent attempts to understand the magnetic models of few-layer RuCl3 and high-spin d7 Co(II) compounds, which have recently been identified as possible alternative platforms for realising the celebrated Kitaev model.

IQC Seminar featuring Ali Assem Mahoud

This talk aims to highlight some mathematical tools that can be used in prob- lems related to quantum computing. We start with monogamy-of-entanglement games and study how to approach them through the Haar measure on unitary matrices. ...