Future graduate students

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.

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.

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.

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. ...

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.