Current graduate students

IQC, CS, & MATH seminar - Eric Culf, University of Waterloo 

Quantum Nano Centre, 200 University Ave West, Room QNC 1201
Waterloo, ON, CA N2L 3G1 +ZOOM

Problems based on the structure of graphs -- for example finding cliques, independent sets, or colourings -- are of fundamental importance in classical complexity. It is well motivated to consider similar problems about quantum graphs, which are an operator system generalisation of graphs. Defining well-formulated decision problems for quantum graphs faces several technical challenges, and consequently the connections between quantum graphs and complexity have been underexplored.

In this work, we introduce and study the clique problem for quantum graphs. Our approach utilizes a well-known connection between quantum graphs and quantum channels. The inputs for our problems are presented as quantum channels induced by circuits, which implicitly determine a corresponding quantum graph. We also use this approach to reimagine the clique and independent set problems for classical graphs, by taking the inputs to be circuits of deterministic or noisy channels which implicitly determine confusability graphs. We show that, by varying the collection of channels in the language, these give rise to complete problems for the classes NP, MA, QMA, and QMA(2). In this way, we exhibit a classical complexity problem whose natural quantisation is QMA(2), rather than QMA, which is commonly assumed.       

To prove the results in the quantum case, we make use of methods inspired by self-testing. To illustrate the utility of our techniques, we include a new proof of the reduction of QMA(k) to QMA(2) via cliques for quantum graphs. We also study the complexity of a version of the independent set problem for quantum graphs, and provide preliminary evidence that it may be in general weaker in complexity, contrasting to the classical case where the clique and independent set problems are equivalent.       

This talk is based on work with Arthur Mehta (arxiv.org/abs/2309.12887)

Tracial embedded strategy: lifting MIP* tricks to MIPco

Quantum Nano Centre, 200 University Ave West, Room QNC 1201
Waterloo, ON CA N2L 3G1

Quantum non-local games have been an important object of study for the operator algebra and computer science community due to the recent ground-breaking result MIP*=RE. Although the majority of the study has been focused on the tensor product model in the non-local games literature recently, the commuting operator model is another model that is also considered in the non-local literature, and the difference between these two models forms the basis for disproving the famous Connes embeddings conjecture. In this talk, I will introduce a new set of strategies for the commuting operator model, the tracial embedded strategy, and sketch the proof that every strategy in the commuting operator model can be approximated by this set of strategies. Using this new characterization, I will present some similarities between the tensor product model and the commuting operator model in the complexity theory realm. This talk is based on the paper "Almost synchronous correlation in the commuting operator model".

Live on YouTube

Join us for Quantum Today, where we sit down with researchers from the University of Waterloo’s Institute for Quantum Computing (IQC) to talk about their work, its impact and where their research may lead.

In this special session, we’ll be joined by Joan Arrow and Özge Gülsayin of the Quantum Ethics Project, a team of researchers exploring the intersection of quantum and society. We’ll discuss how to advocate for the responsible and inclusive development of quantum technologies through education and research, and why an ethics lens is important in even the early stages of technological innovation.

Quantum Nano Centre, 200 University Ave W, Room QNC 0101
Waterloo, ON, CA N2L 3G1

Join the AMO (Atomic, Molecular and Optical) science group for their community meeting.

For this session, Dr. Behrooz Semnani will present a talk on "Flat Optics: A New Opportunity in Quantum Photonics", which will be followed by Q&A and discussion. Coffee and snacks provided!

IQC-QuICS MATH CS Seminar - Junqiao (Randy) Lin, CWI, Amsterdam

Quantum Nano Centre, 200 University Ave W, Room QNC 1201 + ZOOM
Waterloo, ON, CA N2L 3G1

Tracial embedded strategies are a subset of the commuting operator strategies that, in a quantum information sense, have many similarities to a finite-dimensional tensor product strategy. In this talk, I will introduce this set of strategies and sketch the proof that this set of strategies can approximate every strategy in the commuting operator model. Using this new characterization, I will discuss two ingredients for proving MIP*, robust EPR testing and the "rounding" theorem, and how they can be generalized to hold for MIPco. This talk is based on the paper arxiv.org/2304.01940 .

Quantum Nano Centre, 200 University Ave West, Room QNC 0101
Waterloo, ON, CA N2L 3G1

The Institute for Quantum Computing (IQC) now offers two different Quantum Innovators workshops to bring together the most promising young postdoctoral fellows.

Join us from November 6–8 for the theoretical stream, and from November 8–10 for the experimental stream.

Participants may choose to attend just their stream, or attend both streams across the five days.

These workshops held at IQC, University of Waterloo, are partly funded by the Canada First Research Excellence Fund (CFREF) as part of the Transformative Quantum Technologies research initiative.

Schedule

Monday, November 6
Tuesday, November 7
Wednesday, November 8
Thursday,  November 9
Friday, November 10
 

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Neutron Scattering Investigations of Three-Dimensional Topological States

Physics, 200 University Ave West, Room PHY 352
Waterloo, ON, CA N2L 3G1

Magnetic skyrmions represent a unique class of topological magnet characterized by nanometric swirling spin-textures which possess a non-trivial Berry curvature. The combination of their topological stability, unique transport properties, and emergent dynamics has made skyrmions the forerunner for novel spintronic high-density memory and ultra-low power logic device applications. In this thesis, we explore the development and application of various neutron scattering tomography and structured neutron beam techniques for three-dimensional investigations of bulk magnetic topological materials and their defect-mediated dynamical phenomena. Characterization of the disordered multi-phase bulk skyrmion material, Co8Zn8Mn4, was performed through detailed SANS measurements over the entire temperature-magnetic field phase diagram of the material as a function of a dynamic skyrmion ordering sequence. 2D SANS images in combination with micromagnetic simulations reveal a novel disordered-to-ordered skyrmion square lattice transition pathway which represents a new type of non-charge conserving topological transition. In the metastable skyrmion triangular lattice phase, dynamical field-dependent skyrmion responses showed an exotic memory phase in spite of hysteresis protocols involving field-induced saturation into the ferromagnetic phase. Three-dimensional examinations of skyrmion stabilization mechanisms and their dynamical defect pathways were explored using a novel SANS tomography technique which processes multi-projection neutron scattering images as its input. Application of the technique to the ordered thermal equilibrium skyrmion triangular lattice phase yielded the first three-dimensional visualizations of a bulk skyrmion lattice. The reconstructions unveiled a host of exotic skyrmion features, such as branching, segmented, twisting, and filament structures, mediated by three-dimensional topological transitions through two different emergent monopole (MP)-antimonopole (AMP) defect pathways. Finally, the direct identification and determination of topological features and defects in bulk micromagnetic materials, without a priori knowledge of the sample, was explored using holographic approaches for the generation of neutron helical waves. Linear neutron waves in a conventional SANS setup were input on microfabricated gratings which consist of arrays of various q-fold fork-dislocation phase-gratings with nanometric spatial dimensions. Far-field scattering images exhibited doughnut intensity profiles centered on the first diffraction orders, thereby demonstrating the tunable generation of topological neutron states for phase- and topology-matched studies of quantum materials. The amalgamation of these works demonstrates the development and application of novel tools for direct investigations of bulk topological magnetic materials, while uncovering a diverse collection of skyrmion energetics, disorder-dependent dynamics, and three-dimensional topological transition defect pathways. These methods and results open the door to a new generation of neutron scattering techniques for the probing of exotic topological interactions and the complete standalone characterization of quantum materials and their topological phenomena.

Computational Entanglement Theory

Quantum Nano Centre, 200 University Ave W, Room QNC 1201
Waterloo, ON, CA N2L 3G1

Quantum entanglement is an important resource that contributes to the potential of quantum computers over classical computers. It turns out to be an interesting idea to quantify entanglement in states, and there are different approaches to this. We can, for example, consider the number of Bell states that are required to approximately produce a given state or the number of Bell states that can be produced from the state - these correspond to the 'entanglement cost’ and ‘distillable entanglement' respectively. Throughout this, we bear in mind a picture where Alice (A) and Bob (B) own a shared state, and are only able to perform LOCC operations on their respective systems. In practice, however, computational complexity must be taken into account. I will explain some recent developments towards taking computational complexity into account for these operational measures, as well as introducing pseudo-entanglement, and hopefully some quantum cryptography.

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