Quantum@SUN

Title of talk: An Introduction to Effectus Theory

Speaker: Kishan Dayaram

(University of Johannesburg, SA)

Abstract: 

The context of an effectus is a new development in categorical logic which generalizes both classical and quantum logic. An effectus allows for a categorical formulation of quantum mechanics in which the effects of the quantum system are required to form an effect algebra (a generalization of the space of effects of a quantum system).  In this talk, we introduce the context of an effectus and show that it provides new ways of reasoning about quantum systems. In particular, the notion of pure maps is introduced for the context of an effectus. Pure maps are those that are the composition of a compression map and a filter map which corresponds to measuring and forgetting the validity of an effect respectively. Lastly, we show that conditions on a form (a faithful, amnestic functor) may be used to classify certain properties of an effectus.

Bio:

Kishan Dayaram is a final year PhD mathematics student at the University of Johannesburg. He is supervised by Dr Amartya Goswami (UJ) and Prof Zurab Janelidze (Stellenbosch University). His research is on diagram lemmas of homological algebra. His research interests include category theory, group theory and homological algebra.

An announcement may be found here.

Title of talk: Approach to equilibrium of an optical quantum field mode scattering from a non-equilibrium quantum reservoir

Speaker: Prof Marco Merkli

(Memorial University, Canada)

Abstract:

Rigorous derivations of the approach of individual elements of large isolated systems to a state of thermal equilibrium, starting from arbitrary initial states, are exceedingly rare. This is particularly true for quantum mechanical systems. We demonstrate how, through a mechanism of repeated scattering, an approach to equilibrium of this type actually occurs in a specific quantum system. We consider an optical mode passing through a reservoir composed of a large number of sequentially-encountered modes of the same frequency, each of which it interacts with through a beam splitter. We then analyze the dependence of the asymptotic state of this mode on the assumed stationary common initial state of the reservoir modes and on the transmittance of the beam splitters. These results allow us to establish that at small large transmittance, such a mode will, starting from an arbitrary initial system state, approach a state of thermal equilibrium even when the reservoir modes are not themselves initially thermalized.
This talk is intended for an audience which is not necessarily specialized in the topic of open quantum systems or thermalization. It is based on a recent collaboration with S. De Bièvre and P. Parris, available on the arXiv at  https://arxiv.org/pdf/2312.14290.pdf.

Bio:

Marco Merkli is a faculty member of the Department of Mathematics and Statistics at Memorial University in St. John’s, Canada. As a mathematical physicist, his research primarily revolves around elucidating the dynamics of open quantum systems. His expertise lies in developing mathematical tools tailored for analyzing the evolution of systems under external influences. This endeavour aims to establish a robust mathematical framework for the theory of open quantum systems, ensuring the precision of physical predictions and reducing uncertainties in the field. Merkli’s mathematical inquiries have also uncovered novel physical phenomena, particularly concerning the impact of quantum correlations (entanglement) on the dynamics of open systems. He endeavours to foster dialogue between the mathematical and physical communities interested in quantum sciences.

The announcement may be found here.

In today’s Group meeting, Siju Mammen will discuss “An exploration of deep learning for video classification/captioning.”

Title of talk: Decoherence Limiting the Cost to Simulate an Anharmonic Oscillator

Speaker: Dr Tzula Propp

(Delft University of Technology, Netherlands)

Abstract:

Decoherence increases the efficiency with which we simulate the quantum dynamics of an anharmonic oscillator governed by the Kerr effect. As decoherence washes out the fine-grained subPlanck structure associated with phase-space quantum interference in the closed quantum system, open quantum dynamics can be more efficiently simulated using a coarse-grained finite-difference numerical integration. We tie this to the way in which decoherence recovers the semiclassical truncated Wigner approximation (TWA), which strongly differs from the exact closed-system dynamics at times when quantum interference leads to cat states and more general superpositions of coherent states. The regression in quadrature measurement statistics to semiclassical dynamics becomes more pronounced as the initial amplitude of the oscillator grows. Furthermore, this regression to classical dynamics does not have the form of a convex noise model, such as for a depolarizing noise channel, which we derive measurement statistic signatures for. Instead, closed quantum system effects interact with the open system effects, giving rise to distinct open system behavior. Both the interaction between closed and open quantum system effects leading to non-convexity and the regression to classicality increasing with macroscopicity have implications for the quantum advantage achievable on near-term NISQ devices.

Bio:

Originally hailing from San Diego, California in the US, Tzula Benjamin Propp [they/them] studied Physics and Philosophy for their bachelors degree at the College of Wooster, Ohio, and then did a PhD in Physics at the University of Oregon where their dissertation examined theoretical limits to single-photon detection. They then joined University of New Mexico’s Center for Quantum Information and Control as a National Science Foundation postdoctoral fellow to study decoherence and open quantum systems, where they completed the research they will present in this talk. As of August 2023, Tzula has joined QuTech as a postdoc in the Wehner group, researching novel quantum computation and communication applications of the quantum internet with an eye towards positive social benefit, and supporting the development of photonic clients—quantum communication devices to interface with quantum servers—with quantum optical modeling. In addition to research activities, Tzula is actively working to promote resiliency and retention of marginalized researchers in quantum through outreach programs and community organizing and mentorship, recently resulting in their co-founding of the global organization Diversity in Quantum [DiviQ.org] in 2023.

The announcement can be found here.