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Quantum mechanics helps us understand what happens below what a microscope can see, describing the world of atoms, electrons, photons, and more. In celebration of World Quantum Day on April 14th, Dr. John Donohue from the Institute for Quantum Computing will sit down with Exploring by the Seat of Your Pants to explore quantum science and its applications, from light particles and electron waves to superconductors and quantum computers.

No, you have not discovered a Majorana Fermion

Abstract: Is what I tell myself. There was a time when I thought I may have discovered it, others did too. Around 2012 several groups including ours found evidence of these quantum excitations in electrical circuits containing nanowires of semiconductor covered by a superconductor. The dramatic signatures were peaks in conductance that appeared under conditions expected from theory for Majorana modes, which are their own anti-modes and may possess non-Abelian properties. But a few years later, similar features in the data were identified due to an interesting, but a more mundane effect - which we call trivial states such as Andreev bound states. Over time more and more data pointed at the trivial and not at the exotic explanation. But because Majorana claims kept coming, this led to some digging and even retractions. What we learned after 10 years is that we have a much better handle on what effects show up in these nanowires, which positions us well for the ultimate Majorana discovery which we should be able to tell apart from all the non-Majorana things we saw. The second lesson we learned is that materials quality of device constituents, superconductors and semiconductors, as well as how samples are fabricated - are the make-or-break factors for making this happen. So while  I cannot report an exciting physics discovery, I can walk you through the scientific process that took place, a 10-year event of independent value which taught me how to do science better.

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.

IQC Colloquium - Dvira Segal, University of Toronto

Rethinking the operation principles of thermal machines in the nanoscale and quantum domain, we focus on a continuous machine operating in steady state, the quantum absorption refrigerator (QAR), and examine three key questions: (i) How does the strong system-bath interaction affect the device's operation? (ii) What can we learn about the machine from current noise? (iii) What is the impact of coherences within the working fluid on the performance of the quantum machine? 

IQC Special Seminar - Jeremy Young - JILA, University of Colorado

One of the major goals in the field of quantum science is to utilize the properties of quantum mechanics for applications in quantum computation, quantum simulation, and quantum sensing. In order to address this goal, a variety of different many-body quantum platforms have been developed. Many of these quantum platforms exhibit long-range interactions, particularly power-law interactions, including Rydberg atoms, polar molecules, and trapped ions, among others. This gives rise to a natural question: how does the long-range nature of these interactions affect the resulting quantum evolution? 
 

IQC Special Seminar - Bradley Hauer, National Institute of Standards and Technology

In the current paradigm of quantum cavity optomechanics, the relatively weak parametric coupling between an electromagnetic cavity and a mechanical resonator is mediated by an external pump. While this strong cavity drive acts to enhance the optomechanical interaction, it obscures its intrinsic nonlinearity, restricting these systems to bilinear operations on Gaussian states. By increasing this coupling such that it dominates the decoherence rates of the system, one could instead use the fundamental optomechanical nonlinearity to prepare the mechanical resonator into complex, non-Gaussian states...

CS/Math Seminar - Jiahui Liu (UT Austin)

Copy-protection is the task of encoding a program into a quantum state to prevent illegal duplications. A line of recent works studied copy-protection schemes under ``1 -> 2 attacks'': the adversary receiving one program copy can not produce two valid copies. However, under most circumstances, vendors need to sell more than one copy of a program and still ensure that no duplicates can be generated. In this work, we initiate the study of collusion resistant copy-protection in the plain model. Our results are twofold:

Debanjan Chowdhury: The good, the bad and the strange: Unconventional metallic behaviour in the vicinity of Mott insulators

Abstract: In recent years, we have witnessed remarkable experimental breakthroughs in uncovering the intriguing properties of correlated metals in the vicinity of Mott transitions. Describing these phenomena theoretically remains an open challenge. This talk will focus on three recent examples of puzzling electronic behavior near Mott insulating phases and address the various conundrums. In the first part of the talk, I will discuss the microscopic origin of an unconventional T-linear resistivity with Planckian scattering in a quasi-two-dimensional “good” metal with long mean-free path, consisting of highly conducting metallic and Mott insulating layers, respectively. In the second part, I will address the origin of a low-temperature “bad” metallic behavior in the vicinity of a continuous bandwidth-tuned metal-insulator transition in a moiré semiconductor. I will end by presenting some new theoretical insights into the experimental observation of an anomalous particle-hole continuum and overdamped plasmon in the density response of cuprate “strange” metals. 

Landau-Zener tunneling: from weak to strong environment coupling