Events

RAC Journal Club Series featuring Bhaskaran Muralidharan, Indian Institute of Technology, Bombay

Developments in device-independent cryptography

Device-independent cryptography connects the foundational topic of Bell inequalities to the operational task of achieving secure cryptography. With significant progress being made in Bell test experiments, various avenues for further developing device-independent cryptography have been opened. I will give an overview of some background and recent developments in the field, as well as some research questions that should be of interest going forward.

IQC Alum Lecture Series: Urbasi Sinha, Raman Research Institute

In this talk, we cover different interesting aspects of experimental photonic quantum information processing that have been recently explored at the Quantum Information and Computing lab at RRI, Bangalore. We discuss our experiment on the first loophole free violation of the Leggett Garg Inequalities (LGI) as well as the Wigner form of the same (WLGI)[1].

Generation and detection of spin-orbit coupled neutron beams

Structured waves and spin-orbit coupled beams have become an indispensable probe in both light and matter-wave optics [1-2], for neutron specifically, showing distinct scattering dynamics for some samples [3-4]. We present a method of generating neutron orbital angular momentum (OAM) states utilizing 3He neutron spin filters along with four specifically oriented triangular coils and magnetic field shielding. These states are verified via their spin-dependent intensity profiles [5]. The period and OAM number of these spin-orbit states can be altered dynamically via the magnetic field strength within the coils and the total number of coils to tailor the neutron beam towards a particular application or specific material [6].

The Office of Research at the University of Waterloo will be hosting a webinar to provide practical information and answer questions related to the new NSERC Alliance funding options that support Canada’s National Quantum Strategy.

Dissipative landau Zener transition in the weak and strong coupling limits

Landau Zener (LZ) transition is a paradigm to describe a wide range of physical phenomenon. Dissipation is inevitable in realistic devices and can affect the LZ transition probabilities. I will describe how we can model the effect of the environment depending on whether it is weakly or strongly coupled to the system. I will also present our experimental results where we found evidence of crossover from weak to strong coupling limit.

Noncommuting charges: Bridging theory to experiment

Noncommuting conserved quantities have recently launched a subfield of quantum thermodynamics. In conventional thermodynamics, a system of interest and an environment exchange quantities—energy, particles, electric charge, etc.—that are globally conserved and are represented by Hermitian operators. These operators were implicitly assumed to commute with each other, until a few years ago. Freeing the operators to fail to commute has enabled many theoretical discoveries—about reference frames, entropy production, resource-theory models, etc. Little work has bridged these results from abstract theory to experimental reality. This work provides a methodology for building this bridge systematically: we present a prescription for constructing Hamiltonians that conserve noncommuting quantities globally while transporting the quantities locally. The Hamiltonians can couple arbitrarily many subsystems together and can be integrable or nonintegrable. Our Hamiltonians may be realized physically with superconducting qudits, with ultracold atoms, and with trapped ions.

Dynamic qubit allocation and routing for constrained topologies by CNOT circuit re-synthesis

Recent strides in quantum computing have made it possible to execute quantum algorithms on real quantum hardware. When mapping a quantum circuit to the physical layer, one has to consider the numerous constraints imposed by the underlying hardware architecture. Many quantum computers have constraints regarding which two-qubit operations are locally allowed. For example, in a superconducting quantum computer, connectivity of the physical qubits restricts multi-qubit operations to adjacent qubits [1]. These restrictions are known as connectivity constraints and can be represented by a connected graph (a.k.a. topology), where each vertex represents a distinct physical qubit. When two qubits are adjacent, there is an edge between the corresponding vertices.

Andrey Boris Khesin - Massachusetts Institute of Technology

Publicly verifiable quantum money is a protocol for the preparation of quantum states that can be efficiently verified by any party for authenticity but is computationally infeasible to counterfeit. We develop a cryptographic scheme for publicly verifiable quantum money based on Gaussian superpositions over random lattices. We introduce a verification-of-authenticity procedure based on the lattice discrete Fourier transform, and subsequently prove the unforgeability of our quantum money under the hardness of the short vector problem from lattice-based cryptography.

Assessing the Trainability of the Variational Quantum State Diagonalization Algorithm at Scale

Developing new quantum algorithms is a famously hard problem. The lack of intuition concerning the quantum realm makes constructing quantum algorithms that solve particular problems of interest difficult. In addition, modern hardware limitations place strong restrictions on the types of algorithms which can be implemented in noisy circuits. These challenges have produced several solutions to the problem of quantum algorithm development in the modern Near-term Intermediate Scale Quantum (NISQ) Era. One of the most prominent of these is the use of classical machine learning to discover novel quantum algorithms by minimizing a cost function associated with the particular application of interest. This quantum-classical hybrid approach, also called Variational Quantum Algorithms (VQAs), has attracted major interest from both academic and industrial researchers due to its flexible framework and expanding list of applications - most notably optimization (QAOA) and chemistry (VQE). What is still unclear is whether these algorithms will deliver on their promise when implemented at a useful scale, in fact there is strong reason to worry whether the classical machine learning model will be able to train in the larger parameter space. This phenomenon is commonly referred to as the Barren Plateaus problem, which occurs when the training gradient vanishes exponentially quickly as the system size increases. Recent results have shown that some cost functions used in training can be proven to result in a barren plateau, while other cost functions can be proven to avoid them. In this presentation, I apply these results to my 2018 paper where my group developed a new Variational Quantum State Diagonalization (VQSD) algorithm and so demonstrate that this algorithm's current cost function will encounter a Barren Plateau at scale. I then introduce a simple modification to this cost function which preserves its function while ensuring trainability at scale. I also discuss the next steps for this project where I am teaching a team of 6 quantum novices across 4 continents the core calculation I use in this work to expand my analysis to the entire literature of VQAs.

Reference: https://uwspace.uwaterloo.ca/handle/10012/18187