Events

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 Colloquium Featuring Dr. Stephanie Simmons - Photonic

The future global quantum internet will require high-performance matter-photon interfaces. The highly demanding technological requirements indicate that the matter-photon interfaces currently under study all have potentially unworkable drawbacks, and there is a global race underway to identify the best possible new alternative. For overwhelming commercial and quantum reasons, silicon is the best possible host for such an interface. Silicon is not only the most developed integrated photonics and electronics platform by far, isotopically purified silicon-28 has also set records for quantum lifetimes at both cryogenic and room temperatures ...

IQC Colloquium Featuring Anupam Mazumdar, University of Groningen

We are led to create a massive and large spatial quantum superposition to probe the quantum nature of gravity in a laboratory. In particular, to witness the quantum entanglement mediated via the quantum nature of gravity, we will need to prepare a pure quantum state of mass 10^{-15} -10^{-14}Kg with a spatial quantum superposition of 10-100 microns and a coherence time of nearly 1-2 seconds. ...

MATH CS Seminar Featuring Maris Ozols, ASSISTANT PROFESSOR UNIVERSITY OF AMSTERDAM QuSoft

Majority vote is a basic method for amplifying correct outcomes that is widely used in computer science and beyond. While it can amplify the correctness of a quantum device with classical output, the analogous procedure for quantum output is not known. We introduce quantum majority vote as the following task: given a product state ∣ψ_1⟩⊗⋯⊗∣ψ_n⟩ where each qubit ∣ψ_i⟩ is in one of two orthogonal states ∣ψ⟩ or ∣ψ^⊥⟩, output the majority state. We show that an optimal algorithm for this problem achieves worst-case fidelity of 1/2 + Θ(1/n). Under the promise that at least 2/3 of the input qubits are in the majority state, the fidelity increases to 1 − Θ(1/n) and approaches 1 as n increases. ...

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.

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.

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.

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.

IQC Colloquium featuring Xuedong Hu Department of Physics, University at Buffalo, SUNY

Research on the physical implementation of quantum computing has made dramatic progress over the past decade, spearheaded by superconducting qubits and trapped ion qubits, to the degree that small-scale quantum information processors are now within reach. Studies of semiconductor spin qubits, which have often been considered one of the most promising in the long term from the perspective of scalability, have also yielded some important results in the past decade, demonstrating exceptional coherence properties for single spins confined in quantum dots and donors and high-fidelity single-qubit gates. ...

Yong-Baek Kim: Quantum Spin Liquids and Criticality in Multipolar Materials

Abstract: Multipolar quantum materials possess local moments carrying higher-rank quadrupolar or octupolar moments. These higher-rank multipolar moments arise due to strong spin-orbit coupling and local symmetry of the crystal-electric-field environment. In magnetic insulators, the interaction between multipolar local moments on frustrated lattices may promote novel quantum spin liquids. In heavy fermion systems, the interaction between multipolar local moments and conduction electrons may lead to unusual non-Fermi liquids and quantum criticality. In this talk, we first discuss a novel quantum spin ice state, a three-dimensional quantum spin liquid with emergent gauge field, that may have been realized in Ce₂Zr₂O₇ and Ce₂Sn₂O₇, where Ce³⁺ ions carry dipolar-octupolar moments. We present a theoretical analysis of possible quantum spin ice states in this system and compare the theoretical results of dynamical spin structure factors with recent neutron scattering experiments. Next, we present a theoretical model to describe the unusual Kondo effect and quantum criticality in Ce₃Pd₂₀Si₆, where Ce³⁺ moments carry a plethora of dipolar, quadrupolar, and octupolar moments. We show that two consecutive Kondo-destruction-type phase transitions can occur with the corresponding Fermi surface reconstructions. We compare these results with existing experiments and suggest future ultrasound experiments for the detection of emergent quantum critical behaviors.