Events

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.

Math/CS Seminar - Vahid Asadi from IQC

In this talk, we study the problem of designing worst-case to average-case reductions for quantum algorithms. For all linear problems, we provide an explicit and efficient transformation of quantum algorithms that are only correct on a small (even sub-constant) fraction of their inputs into ones that are correct on all inputs. This stands in contrast to the classical setting, where such results are only known for a small number of specific problems or restricted computational models. En route, we obtain a tight Ω(n^2) lower bound on the average-case quantum query complexity of the Matrix-Vector Multiplication problem...

So you want to build a satellite?

Are you curious about the Quantum Encryption and Science Satellite mission, also known as QEYSSat? Are you wondering "Why put quantum in space"? Or perhaps you are curious to know what it takes to put quantum hardware in space? In this talk, we will discuss why it is advantageous to have quantum in space. We will also explore the various design challenges that need to be considered for space hardware. Finally, we will discuss the history of quantum space activities at the Institute for Quantum Computing, particularly QEYSSat, which is a joint project between the Canadian Space Agency (CSA) and the University of Waterloo.

CS/Math Seminar - Luowen Qian, Boston University in person and on ZOOM

Pseudorandom states (PRS) are efficiently constructible states that are effectively Haar random against efficient observers. Recently, this notion has found its influence in many fields like quantum information, quantum gravity, and quantum complexity. ...

Roger Melko: Language models for quantum simulation

Abstract: As the frontiers of artificial intelligence advance more rapidly than ever before, generative language models like ChatGPT are poised to unleash vast economic and social transformation. In addition to their remarkable performance on typical language tasks (such as writing undergraduate research papers), language models are being rapidly adopted as powerful ansatze states for quantum many-body systems.  In this talk, I will discuss the use of language models for learning quantum states realized in experimental Rydberg atom arrays. By combining variational optimization with data-driven learning using qubit projective measurements, I will show how language models are poised to become one of the most powerful computational tools in our arsenal for the design and characterization of quantum simulators and computers.

The Quantum Shorts festival celebrates independent short films inspired by quantum mechanics. Using ideas like the uncertainty principle and many-worlds interpretation, filmmakers from around the world have created five-minute wonders.

CS/Math Seminar - Daochen Wang QuICS, UMD

The divide-and-conquer framework, used extensively in classical algorithm design, recursively breaks a problem into smaller subproblems, along with some auxiliary work, to give a recurrence relation for the classical complexity. We describe a quantum divide-and-conquer framework that, in certain cases, yields quantum speedup through an analogous recurrence relation for the quantum query complexity....

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.